JP2014188407A - Composite semipermeable membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane having higher water permeability than heretofore while keeping nearly the same salt removability as heretofore.SOLUTION: A composite separation membrane of this invention is a composite semipermeable membrane which is provided with: a substrate; a porous support layer provided on the substrate; and a separation functional layer which is provided on the porous support layer and has a continuously repeated pleat structure including protrusions and recesses on a surface. The porous support layer has a multilayer structure including a first layer and a second layer existing at the side of the separation functional layer rather than the first layer. The thicknesses x(μm) of the first layer and the thickness y(μm) of the second layer satisfy the relational expression of (x/y)≥10. The thickness of the second layer is 10 μm or less, and the porosity of the first layer is 60% or more and is higher than that of the second layer.

Description

  The present invention relates to a composite semipermeable membrane useful for the selective separation of liquid mixtures. The composite semipermeable membrane according to the present invention can be suitably used for desalination of seawater or brine, for example.

  Regarding the separation of mixtures, there are various techniques for removing substances (eg, salts) dissolved in a solvent (eg, water), but in recent years, the use of membrane separation methods has expanded as a process for saving energy and resources. doing. Membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes can be used for beverages such as seawater, brine, and water containing harmful substances. It is used to obtain water, to manufacture industrial ultrapure water, to treat wastewater, to recover valuable materials.

  The majority of currently marketed reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes, which have an active layer in which a gel layer and a polymer are crosslinked on a porous support membrane, and monomers on the porous support membrane. There are two types, one having an active layer obtained by polycondensation. Among these, the composite semipermeable membrane obtained by coating a porous support membrane with a separation functional layer made of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide has water permeability and salt removal. Widely used as a highly reliable separation membrane (Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 9-19630 JP 2005-169332 A

However, in recent years, in desalination plants that use composite semipermeable membranes as reverse osmosis membranes, in order to further reduce running costs, higher water permeability is required for composite semipermeable membranes, and there is room for improvement. It was.
Accordingly, an object of the present invention is to provide a composite semipermeable membrane having a higher water permeability than the conventional one while maintaining a salt removing property comparable to the conventional one.

In order to achieve the above object, the composite semipermeable membrane of the present invention has the following constitution.
<1> Base material, a porous support layer provided on the base material, and a separation functional layer provided on the porous support layer and having a pleat structure including convex portions and concave portions that are continuously repeated on the surface A composite semipermeable membrane comprising:
The porous support layer has a multilayer structure including a first layer and a second layer present on the separation function layer side of the first layer, and the thickness x (μm) of the first layer; The thickness y (μm) of the second layer satisfies the relational expression (x / y) ≧ 10, the thickness of the second layer is 10 μm or less, and the porosity of the first layer is that of the second layer. A composite semipermeable membrane that is higher than the porosity and has a porosity of 60% or more in the first layer.
<2> The composite semipermeable membrane according to <1>, wherein the thickness of the second layer is 5 μm or less.
<3> The composite semipermeable membrane according to <1> or <2>, wherein the standard deviation of the thickness of the second layer is 1.0 μm or less.
<4> The composite semipermeable membrane according to any one of <1> to <3>, wherein the second layer contains fine particles.
<5> A 10-point average surface roughness in the separation functional layer by arbitrarily selecting 10 sections having a length of 2.0 μm in the film surface direction of the composite semipermeable membrane and observing each of the sections with an electron microscope. Is measured, the line density of the convex part having a height of 1/5 or more of the 10-point average surface roughness is obtained, and the average of the line density obtained at the 10 points is 12.0 pieces / μm or more. And the average height of the convex portions having a height of 1/5 or more of the 10-point average surface roughness is obtained, and the average of the average height obtained at the 10 locations is 110 nm or more, The composite semipermeable membrane according to any one of <1> to <4>.
<6> The composite semipermeable membrane according to any one of <1> to <5>, wherein the base material is a long-fiber nonwoven fabric containing polyester.

  The present invention realizes high water permeability in the composite semipermeable membrane while maintaining the same degree of salt removal as before, and can reduce the running cost in the water production plant using the composite semipermeable membrane. .

FIG. 1 is a drawing schematically showing a method for measuring the height of a convex portion in a fold structure on the surface of a separation functional layer.

1. Composite semipermeable membrane The composite semipermeable membrane according to the present invention comprises a base material, a porous support layer provided on the base material, and a convex portion and a concave portion provided on the porous support layer and continuously repeated. And a separation functional layer having a pleat structure including

(1-1) Support membrane The support membrane comprises a base material and a porous support layer provided on the base material, and has substantially no separation performance such as ions, and is strong in the separation functional layer. Can be given.
The thickness of the support membrane affects the strength of the composite semipermeable membrane and the packing density when the composite semipermeable membrane is used as a membrane element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support membrane is preferably in the range of 30 to 300 μm, more preferably in the range of 50 to 250 μm.

In the present specification, unless otherwise specified, the thickness of a layer or film means an average value. Here, the average value represents an arithmetic average value.
The thickness of the layer or film is obtained by calculating the average value of the thicknesses of 20 points measured at intervals of 20 μm in the direction orthogonal to the thickness direction in the cross-sectional observation of the layer or film (the surface direction of the layer or film or the horizontal direction). It is done.

(1-1-1) Porous Support Layer The porous support layer in the present invention has a multilayer structure including a first layer and a second layer present on the separation functional layer side with respect to the first layer. preferable.
Among these, the first layer is preferably a layer on the surface of the porous support layer on the substrate side, that is, preferably in contact with the substrate. The second layer is preferably a layer on the surface of the porous support membrane on the separation functional layer side.
Further, the porous support layer has a two-layer structure, the first layer is formed on the surface of the substrate, the second layer is formed on the surface of the first layer, and the separation functional layer is formed on the surface of the second layer. More preferably.

  As will be described in detail later, it is preferable that the first layer plays a role of holding the material (polymer solution) forming the separation functional layer and efficiently transferring it to the surface of the porous support layer, and the second layer is separated. When the functional layer is formed, it preferably plays a role of controlling the linear density of the convex portions on the surface of the separation functional layer.

The surface of the porous support layer, that is, the surface facing the separation functional layer, preferably has a granular structure.
Having a granular structure means that the surface of the porous support layer or a layer in the vicinity thereof contains particles, so that the surface of the porous support layer has an uneven structure. The layer on the surface of the porous support layer containing particles or the adjacent layer containing the particles is preferably the second layer described above, and the layer on the surface of the porous support layer containing particles is the second layer. More preferred.

The particles for forming the granular structure are preferably fine particles having a diameter of 10 nm or more and 70 nm or less because the particle density is increased.
The higher the grain density, the more starting points for the formation of the pleat structure in the separation functional layer, and the higher the linear density of the protrusions on the surface of the separation functional layer, the greater the surface area of the separation functional layer and the better the water permeability. It becomes a structure. This is considered to be due to the following reason.

In the case where the separation functional layer is mainly composed of polyamide by interfacial polycondensation between a polyfunctional amine and a polyfunctional acid halide, in the formation of the separation functional layer, the above-described support film composed of a base material and a porous support layer is formed on the support membrane. By contacting the polyfunctional amine aqueous solution, the polyfunctional amine aqueous solution is held inside the porous support layer, and the polyfunctional amine aqueous solution is transferred from the inside of the porous support layer to the surface during polycondensation.
As the layer capable of holding the polyfunctional amine aqueous solution of the porous support layer and transferring it to the surface, the first layer described above is preferably used.
In the present specification, “X contains Y as a main component” means that Y occupies 50% by weight or more of X, and includes a configuration in which X substantially contains only Y.

The surface of the porous support layer functions as a reaction field for polycondensation. By supplying the polyfunctional amine aqueous solution from the inside of the porous support layer to the reaction field, the convex portion of the separation functional layer grows.
As described above, when the particle density on the surface of the porous support layer as a reaction field is large, the number of growth points of the convex portions increases, and as a result, the linear density of the convex portions of the separation functional layer increases.
In general, the surface of a porous support layer having a high grain density is dense and has a low porosity and a small pore diameter. On the other hand, if the porosity inside the porous support layer is high, the pore size is large, and the continuity is high, the monomer constituting the separation functional layer is preferably supplied uniformly and efficiently to the reaction field. In addition, a separation functional layer having a uniform thickness and a large convex portion is formed.

  In this way, the uniformity and thickness of the separation functional layer and the height of the ridges in the fold structure are determined by the supply amount and uniformity of the polyfunctional amine aqueous solution from the inside of the porous support layer. The linear density of the convex portions of the separation functional layer is determined by the surface structure on the functional layer side.

  The porous support layer in the present invention is a first layer that holds and efficiently transports a polyfunctional amine aqueous solution, and is located closer to the separation function layer than the first layer, and the line of the convex portion of the formed separation function layer It is preferable to include a second layer for controlling the density. In particular, the first layer is preferably in contact with the substrate, and the second layer is preferably located on the outermost layer of the porous support layer so as to be in contact with the separation functional layer. Since the porosity of the surface of the porous support layer is low (that is, the grain density is high), it is possible to increase the linear density of the protrusions in the pleated structure described above, thereby increasing the surface area of the separation functional layer. High water permeability can be obtained. Furthermore, since the inside of the porous support layer has a structure with a high porosity having many highly continuous pores, the height of the convex portion of the separation function layer is increased.

The first layer plays a role of transferring an aqueous polyfunctional amine solution necessary for forming the separation functional layer to the polymerization field. In order to efficiently transfer the monomer, it is preferable to have continuous pores. In particular, the pore diameter is preferably 0.1 μm or more and 1 μm or less. Moreover, it is preferable that the porosity at this time is 60% or more.
By adjusting the concentration of the polymer solution used when forming the first layer, the pore size of the first layer can be controlled. The pore diameter can be determined by a mercury intrusion method or a gas adsorption method.
As will be described in detail later, the porosity of the first layer can be adjusted to 60% or more by adjusting the concentration of the polymer solution to 13% by weight or more and 16% by weight or less.
The porosity of the first layer can be obtained by cross-sectional observation by electron microscope observation described in Examples described later.

As described above, the second layer serves as a reaction field for polycondensation and holds and releases the monomer that forms the separation functional layer, thereby supplying the monomer to the separation functional layer to be formed, and the convex portion. It also serves as a starting point for growth.
Here, the porous support layer having a high particle density in the second layer can form a separation functional layer having convex portions having a high linear density. However, since the particle density is high and dense, the monomer transfer rate to the polycondensation field is high. Is small, and the convex portions to be formed are small and non-uniform.
Therefore, the first layer, which is a layer having continuous pores, is disposed on the substrate side, and a dense granular layer is formed as a second layer to form a porous support layer that is thinly laminated on the first layer. As a result, the transfer rate of the monomer can be supplemented, so that a uniform separation functional layer can be formed.
As one method for forming the second layer having a lower porosity than the first layer, the concentration of the polymer solution forming the second layer is set higher than the concentration of the polymer solution forming the first layer. To do. Details of the concentration are as described later.
Thus, in order to simultaneously control the uniformity and linear density of the convex portions, it is preferable that the porous support layer includes a first layer and a second layer formed thereon.

In particular, when the thickness x (μm) of the first layer and the thickness y (μm) of the second layer satisfy the relational expression (x / y) ≧ 10, the convex portion having a high linear density is formed on the surface. This is preferable because the separation functional layer can be obtained and at the same time the size of the convex portion can be obtained sufficiently. The thickness ratio (x / y) may be 12 or more or 15 or more. Moreover, the thickness ratio (x / y) is 50 or less, whereby the height of the convex portion of the pleated structure can be controlled in a more preferable range.
Moreover, it is preferable that the thickness of a 1st layer exists in the range of 5-150 micrometers, More preferably, it exists in the range of 10-100 micrometers.
The thickness of the second layer is preferably 10 μm or less, more preferably 5 μm or less. High water permeability is obtained because the thickness of the second layer is in this range. Further, the thickness of the second layer is preferably 1 μm or more, and more preferably 2 μm or more. When the thickness of the second layer is within this range, the pleat structure can be reliably controlled.
Furthermore, if the standard deviation of the thickness of the second layer is 1.0 μm or less, it is possible to make the transfer rate from each starting point of the convex growth to the polymerization field of the monomer uniform, resulting in a uniform height. Since a convex part can be formed, it is more preferable.
The thicknesses of the first layer and the second layer can be obtained mainly by a microscope.

The porous support layer in the present invention preferably contains the following materials as main components. As the material for the porous support layer, polysulfone, polyethersulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, or homopolymer or copolymer such as polyphenylene oxide, alone or in a blend Can be used.
Here, cellulose acetate, cellulose nitrate and the like are used as the cellulose polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and the like can be used as the vinyl polymer.

Among them, a homopolymer such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, or a copolymer thereof is preferable.
More preferred is cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone.
Among these materials, polysulfone can be particularly preferably used because of its high chemical, mechanical and thermal stability and easy molding.
Specifically, it is preferable to use polysulfone composed of repeating units represented by the following chemical formula as the main component of the porous support layer because the pore diameter can be easily controlled and the dimensional stability is high.

The polysulfone used in the present invention preferably has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a developing solvent and polystyrene as a standard substance. It is within the range of 200,000, more preferably 15,000-100,000.
When the Mw is 10,000 or more, preferable mechanical strength and heat resistance can be obtained as the porous support layer. Moreover, when Mw is 200,000 or less, the viscosity of the solution falls within an appropriate range, and good moldability can be realized.

The porous support layer is prepared by, for example, casting an N, N-dimethylformamide (hereinafter also referred to as “DMF”) solution in which the above polysulfone is dissolved to a certain thickness on a substrate. Can be obtained by wet coagulation in water. Most of the surface of the support membrane obtained by this method can have fine pores having a diameter of 1 to 30 nm.
Moreover, it is preferable that the thickness of a porous support layer exists in the range of 10-200 micrometers, More preferably, it exists in the range of 20-150 micrometers.

  When the porous support layer contains polysulfone, the polysulfone content in the first layer and the polysulfone content in the second layer are both preferably 50% by mass or more. Moreover, it is preferable that the content rate of polysulfone is 50 mass% or more in the whole porous support layer.

(1-1-2) Base material Examples of the base material constituting the support film include a polyester polymer, a polyamide polymer, a polyolefin polymer, or a mixture or copolymer thereof. Among these, a polyester polymer is preferable because an excellent support film can be obtained due to mechanical strength, heat resistance, water resistance, and the like.

The polyester polymer used in the present invention is a polyester composed of an acid component and an alcohol component, and is preferably the main component of the substrate in the present invention.
Examples of the acid component include aromatic carboxylic acids such as terephthalic acid, isophthalic acid, and phthalic acid; aliphatic dicarboxylic acids such as adipic acid and sebacic acid; and alicyclic dicarboxylic acids such as cyclohexanecarboxylic acid.
Further, as the alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, or the like can be used.

  Examples of the polyester polymer include polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polylactic acid resin, and polybutylene succinate resin. Examples include coalescence. Among them, a polyethylene terephthalate homopolymer or a copolymer thereof is preferably used because it is particularly excellent in production cost.

The base material in the present invention is a cloth-like material made of the polymer or the like. It is preferable to use a fibrous base material for the fabric in terms of strength, unevenness forming ability, and fluid permeability.
As a base material, both a long fiber nonwoven fabric and a short fiber nonwoven fabric can be used preferably.

In particular, the long fiber nonwoven fabric is excellent in permeability when casting a polymer solution, which is a material of the porous support layer, on the base material, due to peeling of the porous support layer, fluffing of the base material, etc. It is possible to prevent the film from becoming non-uniform and causing defects such as pinholes.
In addition, since the base material is made of a long-fiber non-woven fabric composed of thermoplastic continuous filaments, it suppresses non-uniformity and membrane defects during casting of a polymer solution caused by fuzz that occurs when a short-fiber non-woven fabric is used. be able to.
Furthermore, tension is applied to the film forming direction in the continuous film formation of the separation membrane.
Also from the above, it is preferable to use a long-fiber nonwoven fabric that is more excellent in dimensional stability for the substrate. The long fiber nonwoven fabric is a nonwoven fabric having an average fiber length of 30 cm or more and an average fiber diameter of 1 to 100 μm.

In the long-fiber non-woven fabric or the short-fiber non-woven fabric, the fibers in the surface layer on the side opposite to the porous support layer are preferably longitudinally oriented as compared with the fibers in the surface layer on the porous support layer side in terms of moldability and strength. The longitudinal alignment will be described later.
By taking such a structure, not only a high effect of preventing the membrane breakage of the composite semipermeable membrane by maintaining the strength is realized, but also the porous support layer when imparting irregularities to the separation functional layer, Formability as a laminate including a substrate is also improved, and the uneven shape on the surface of the separation functional layer is stabilized, which is preferable.

  More specifically, the fiber orientation degree in the surface layer on the side opposite to the porous support layer of the long fiber nonwoven fabric or the short fiber nonwoven fabric is preferably 0 ° to 25 °. Moreover, it is preferable that the orientation degree difference between the fiber orientation degree in the surface layer opposite to the porous support layer and the fiber orientation degree in the surface layer on the porous support layer side is 10 ° to 90 °.

The manufacturing process of the composite semipermeable membrane and the manufacturing process of the element include a heating process, but a phenomenon occurs in which the porous support layer or the separation functional layer contracts due to the heating. This is particularly noticeable in the width direction where no tension is applied in continuous film formation.
Since shrinkage causes problems in dimensional stability and the like, a substrate having a small thermal dimensional change rate is desired. In the nonwoven fabric, when the difference between the fiber orientation degree on the surface layer opposite to the porous support layer and the fiber orientation degree on the porous support layer side surface layer is 10 ° to 90 °, the change in the width direction due to heat is suppressed. Can also be preferable.

  In this specification, the “degree of fiber orientation” is an index indicating the direction of fibers of the nonwoven fabric base material constituting the porous support layer. A nonwoven fabric base material when the film forming direction for continuous film formation, that is, the longitudinal direction of the nonwoven fabric base material is 0 °, and the direction perpendicular to the film forming direction, that is, the width direction of the nonwoven fabric base material is 90 °. This refers to the average angle of the constituent fibers. Accordingly, the closer to 0 ° the fiber orientation, the longer the orientation, and the closer to 90 °, the lateral orientation.

The fiber orientation degree is measured as follows.
Ten small sample samples are taken at random from the nonwoven fabric, and the surface of the sample is photographed at 100 to 1000 times with a scanning electron microscope. In the photographed image, 10 fibers are selected from each sample, and for a total of 100 fibers, the longitudinal direction (longitudinal direction, film forming direction) of the nonwoven fabric is 0 °, and the width direction (lateral direction) of the nonwoven fabric is 90 degrees. Measure the angle at °. The average value of the measured angles is calculated as the fiber orientation by rounding off the first decimal place.

  Moreover, it is preferable from the point of mechanical strength and a packing density that the thickness of a base material exists in the range of 10-250 micrometers, More preferably, it exists in the range of 20-200 micrometers.

(1-2) Separation Functional Layer The separation functional layer is a layer that bears a solute separation function in the composite semipermeable membrane. The composition such as the composition and thickness of the separation functional layer is set in accordance with the intended use of the composite semipermeable membrane.
In general, the pleat structure on the surface of the separation functional layer has a convex portion and a concave portion that are continuously repeated. If the height of the convex portion (that is, the height of the fold) is increased (the fold is enlarged), the water permeability is improved. However, the salt permeability increases.
It is thought that high salt removal and water permeability can be achieved by expanding the pleats as a result of the relative increase in water permeation with respect to salt permeation due to increased water permeability. This is because the salt removability is maintained at a high level and does not suppress the permeability of the salt. Rather, the presence of excessively enlarged ridge protrusions leads to membrane deformation and membrane structure breakage at the time of pressurization, thereby reducing the salt removability.

In particular, in the case of a composite semipermeable membrane used in a desalination plant for seawater desalination operated at high pressure, this tendency tends to appear in performance.
As a result of diligent investigation focusing on the structure of the convex portion in the fold structure on the surface of the separation functional layer, the present inventors precisely controlled the linear density and height of the convex portion, and made the size of the convex portion uniform. As a result, it has been found that both high salt removability and high water permeability can be achieved.

In the present invention, the convex portion of the separation functional layer used when determining the average linear density and the average height refers to a convex portion having a height of 1/5 or more of the 10-point average surface roughness. The 10-point average surface roughness is a value obtained by the following calculation method.
First, a cross section perpendicular to the film surface is observed with an electron microscope at a magnification described later. The size of the cross section to be observed is such that the length in the horizontal direction of the film surface (hereinafter sometimes referred to as “film surface direction”) is 2.0 μm or more, and the cross section of the separation functional layer can be observed. Good.
In the obtained cross-sectional image, a surface shape 1 (curve having a pleated structure) in which the convex portion and the concave portion are continuously repeated on the surface of the separation functional layer is observed (FIG. 1). About this curve, the roughness curve defined based on ISO4287: 1997 is calculated | required. Then, a cross-sectional image is extracted with a width of 2.0 μm in the direction of the average line of the roughness curve (FIG. 1).
The average line is a straight line defined based on ISO 4287: 1997, and is drawn so that the total area of the region surrounded by the average line and the roughness curve is equal above and below the average line in the measurement length. Which is parallel to the film surface direction.

In the extracted cross-sectional image having a width of 2.0 μm, the height of the convex portion (H) and the depth of the concave portion (D) in the separation functional layer are measured using the average line as the reference line 2.
The absolute value of the heights H1 to H5 of the five convex portions from the highest convex portion (H1) to the fifth height (H5) gradually decreasing, and the deepest concave portion (D1) The average value is calculated for the absolute values of the depths D1 to D5 of the five recesses from the depth gradually to the fifth depth (D5), and the sum of the absolute values of the two average values obtained. Is calculated. The sum thus obtained is the 10-point average surface roughness.

  The height of the convex portion and the depth of the concave portion of the separation functional layer can be analyzed using an electron microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM). For example, a composite semipermeable membrane sample is embedded with an epoxy resin, and then subjected to a dyeing treatment with osmium tetroxide or ruthenium tetroxide, preferably osmium tetroxide, and is further subjected to surface processing with a glass knife or a diamond knife and an ultrafine film of 100 nm or less. Thin sections are prepared and observed using a transmission electron microscope at an acceleration voltage of 50 to 200 kV. As the transmission electron microscope, an electron microscope such as Hitachi, H7100FA can be used.

  The observation magnification is preferably 5,000 to 100,000 times, and preferably 10,000 to 50,000 times for obtaining the height of the convex portions and the depth of the concave portions of the separation functional layer. In order to obtain the height of the convex portion and the depth of the concave portion of the separation functional layer, it can be directly measured with a scale or the like in consideration of the observation magnification from the obtained electron micrograph.

For the composite semipermeable membrane, by counting the number of convex portions that are 1/5 or more of the 10-point average surface roughness obtained above, the number of convex portions per unit length, that is, the line of the convex portion The density can be determined. Here, since each cross section has a width of 2.0 μm in the direction of the average line 2 of the roughness curve, a convex portion that is 1/5 or more of the 10-point average surface roughness is present. When t pieces are present, the linear density is (t pieces / 2.0 μm).
Ten cross sections are arbitrarily selected in the composite semipermeable membrane, the linear density is determined by the above method, and the arithmetic average of the linear densities determined at the ten locations is defined as the average linear density.

The average linear density of the convex portions of the separation functional layer in the present invention is preferably 12.0 pieces / μm or more, more preferably 13.0 pieces / μm or more. The average linear density of the convex portions of the separation functional layer is preferably 50 pieces / μm or less, and more preferably 40 pieces / μm or less.
When the average linear density is 12.0 pieces / μm or more, the composite semipermeable membrane including the separation functional layer can obtain sufficient water permeability, and can further suppress deformation of the convex portion during pressurization. Stable membrane performance can be obtained. Further, when the average linear density is 50 pieces / μm or less, the protrusions are sufficiently grown, and a composite semipermeable membrane having a desired water permeability can be easily obtained.

In this invention, the average height of the convex part of a separation function layer is a value measured about the convex part which has a height of 1/5 or more of 10-point average surface roughness. Specifically, the average height of the convex portions is measured as follows.
In the composite semipermeable membrane, arbitrarily select 10 sections having a length in the film surface direction of 2.0 μm, observe each of the sections with an electron microscope, and determine the 10-point average surface roughness in the separation functional layer, Calculated in the same manner as the average linear density and method described above. The height of the convex part having a height of 1/5 or more of the 10-point average surface roughness is measured, and the average height per convex part is calculated. This is called the average height. Furthermore, the average of the average heights is obtained by calculating the arithmetic average of the average heights obtained at the 10 locations.

In the present invention, the average height of the convex portions of the separation functional layer is preferably 110 nm or more, more preferably 120 nm or more. In addition, the height of the convex portion of the separation functional layer is preferably 1000 nm or less, and more preferably 800 nm or less.
When the height of the convex portion is 110 nm or more, a composite semipermeable membrane having sufficient water permeability can be easily obtained. Moreover, when the height of the convex portion is 1000 nm or less, stable membrane performance can be obtained without collapsing the convex portion shape even when the composite semipermeable membrane is operated at a high pressure.

  The composition such as the composition and thickness of the separation functional layer is set in accordance with the purpose of use of the composite semipermeable membrane, but the thickness of the separation functional layer is usually 0. The range of 01 to 1 μm is preferable, and the range of 0.1 to 0.5 μm is more preferable.

  The separation functional layer may contain polyamide as a main component. The polyamide constituting the separation functional layer can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. Here, it is preferable that at least one of the polyfunctional amine or the polyfunctional acid halide contains a trifunctional or higher functional compound.

  The polyfunctional amine refers to an amine having at least one primary amino group in one molecule and further having at least one of at least one primary amino group and secondary amino group.

Examples of the polyfunctional amine include phenylenediamine, xylylenediamine, and 1,3,5-triaminobenzene in which two amino groups are bonded to the benzene ring in any of the ortho, meta, and para positions. Aromatic polyfunctional amines such as 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine and 4-aminobenzylamine; aliphatic amines such as ethylenediamine and propylenediamine; Examples include alicyclic polyfunctional amines such as 2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, and 4-aminoethylpiperazine.
Among them, considering the selective separation property, permeability, and heat resistance of the membrane, the polyfunctional amine is an aromatic polyfunctional having 2 to 4 primary amino groups and / or secondary amino groups in one molecule. An amine is preferred. As such a polyfunctional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, it is more preferable to use m-phenylenediamine (hereinafter sometimes referred to as “m-PDA”) in view of availability and ease of handling.

  These polyfunctional amines may be used alone or in combination of two or more. When using 2 or more types simultaneously, the said amines may be combined and the said amine and the amine which has at least 2 secondary amino group in 1 molecule may be combined. Examples of the amine having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidylpropane.

The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule.
For example, examples of the trifunctional acid halide include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and the like.
Examples of the bifunctional acid halide include aromatic bifunctional acid halides such as biphenyl dicarboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalene dicarboxylic acid chloride; adipoyl chloride, sebacoyl chloride, and the like. Aliphatic bifunctional acid halides; cycloaliphatic difunctional acid halides such as cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, and tetrahydrofuran dicarboxylic acid dichloride can be exemplified.

  In consideration of the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride. In view of selective separation of the membrane and heat resistance, the polyfunctional acid chloride is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Among these, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination of two or more.

2. Next, a method for producing a composite semipermeable membrane according to the present invention will be described. The production method includes a support film forming step including a base material and a porous support layer and a separation functional layer forming step.

(2-1) Formation process of support film The formation process of the support film includes a process of forming a layer to be the first layer of the porous support layer on the substrate, a process of forming a thin film to be the second layer, and A step of laminating the second layer on the surface of the first layer may be included. Alternatively, a step of forming the first layer and a step of forming the second layer directly on the surface of the first layer may be included.

  The step of forming the first layer on the base material includes a step of applying a polymer solution constituting the first layer to the base material, a step of impregnating the base material with the polymer solution, and impregnating the polymer solution. The base material was immersed in a coagulation bath of a solution (hereinafter, simply referred to as “non-solvent”) having a lower solubility of the polymer than the good solvent of the polymer to coagulate the polymer. A step of forming a three-dimensional network structure of molecules may be included. Moreover, the process which melt | dissolves the polymer which is a component of the 1st layer in the good solvent of the polymer and prepares a polymer solution may be further included.

  In order to obtain a layer having a predetermined structure, it is necessary to control the impregnation of the polymer solution into the substrate. In order to control the impregnation of the polymer solution into the substrate, for example, a method of controlling the time until the polymer solution is immersed on the non-solvent after the polymer solution is applied on the substrate, or the temperature of the polymer solution or A method of adjusting the viscosity of the polymer solution by controlling the concentration can be mentioned, and these production methods can be combined.

  After applying the polymer solution on the substrate, the time for dipping in the coagulation bath is preferably in the range of usually 0.1 to 5 seconds. If the time until dipping in the coagulation bath is within this range, the organic solvent solution containing the polymer is sufficiently impregnated between the fibers of the base material and then solidified. In addition, what is necessary is just to adjust the preferable range of time until it immerses in a coagulation bath suitably with the viscosity of the polymer solution to be used. In addition, another 3rd layer may be formed between a 1st layer and a base material, and the 1st layer may be formed on it.

  When the polymer solution A forming the first layer of the porous support layer contains polysulfone, the polysulfone concentration (that is, the solid content concentration a) of the polymer solution A is preferably 13% by mass or more, more preferably It is 14 mass% or more. Further, the solid content concentration a is preferably 16% by mass or less, and more preferably 15% by mass or less. When the solid content concentration a is 13% by mass or more, the communication hole is formed to be relatively small, so that a desired hole diameter can be easily obtained. Further, when the solid content concentration a is 16% by mass or less, the phase separation can sufficiently proceed before the solidification of the polymer, so that a porous structure having a high porosity can be easily obtained.

When using a polysulfone, the temperature of the polymer solution A at the time of application of the polymer solution is usually within a range of 10 to 60 ° C. Within this range, the polymer solution A does not precipitate and is solidified after the organic solvent solution containing the polymer is sufficiently impregnated between the fibers of the substrate.
As a result, the porous support membrane is firmly bonded to the substrate by the anchor effect, and the porous support membrane of the present invention can be obtained. Note that the preferable temperature range of the polymer solution A may be appropriately adjusted depending on the viscosity of the polymer solution used.

  The application of the polymer solution A onto the substrate can be performed by various coating methods, but since an accurate amount of the coating solution can be supplied, pre-metering coating methods such as die coating, slide coating, curtain coating, etc. are preferably applied. Is done.

  The good solvent of the present invention dissolves a polymer material. The good solvent used in the present invention varies depending on the type of polymer. For example, N-methyl-2-pyrrolidone (NMP); tetrahydrofuran; dimethyl sulfoxide; amides such as tetramethylurea, dimethylacetamide, dimethylformamide; acetone, And lower alkyl ketones such as methyl ethyl ketone; esters and lactones such as trimethyl phosphate and γ-butyrolactone; and mixed solvents thereof.

  Examples of the non-solvent of the resin include water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, and low molecular weight. Examples thereof include aliphatic hydrocarbons such as polyethylene glycol, aromatic hydrocarbons, aliphatic alcohols, or mixed solvents thereof.

As the coagulation bath, water is usually used, but any non-solvent that does not dissolve the polymer may be used. The film form of the support film changes depending on the composition, and thereby the film forming property of the composite film also changes.
Further, the temperature of the coagulation bath is preferably -20 ° C to 100 ° C. More preferably, it is 10-30 degreeC. If it is higher than this range, the vibration of the coagulation bath surface becomes intense due to thermal motion, and the smoothness of the film surface after film formation tends to decrease. On the other hand, if it is too low, the coagulation rate will be slow, causing a problem in film forming properties.

Further, the polymer solution A may contain an additive for adjusting the pore diameter, porosity, hydrophilicity, elastic modulus and the like of the porous support membrane.
Additives for adjusting the pore size and porosity include water; alcohols; water-soluble polymers such as polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol and polyacrylic acid or salts thereof; lithium chloride, sodium chloride, calcium chloride Inorganic salts such as lithium nitrate; formaldehyde, formamide and the like are exemplified, but not limited thereto.
Examples of additives for adjusting hydrophilicity and elastic modulus include various surfactants.

For the thin film to be the second layer, the polymer solution B constituting the second layer is coated on a smooth substrate and immersed in a non-solvent coagulation bath in which the solubility of the polymer is small compared to a good polymer solvent. The polymer is solidified to form a thin layer, and then only this thin layer is taken out.
As a method of laminating the second layer on the surface of the first layer, for example, a method of pressure bonding by heat can be mentioned. It can also be obtained by coating the surface of the first layer with a solution containing fine particles or by spray coating. The same applies to the case where the first layer is stacked on another layer different from the first layer.

When the polymer solution B forming the second layer contains polysulfone, the polysulfone concentration (that is, the solid content concentration b) of the polymer solution B is preferably 18% by mass or more, more preferably 19% by mass or more. More preferably, it is 20% by mass or more. Further, the solid content concentration b is preferably 35% by mass or less, and more preferably 30% by mass or less.
By making the polysulfone concentration of the polymer solution B higher than the polysulfone concentration of the polymer solution A, the porosity of the first layer can be made higher than the porosity of the second layer. In particular, the ratio of concentration based on mass% (concentration of polymer solution A / concentration of polymer solution B) is preferably 1/2 or more, and preferably 3/4 or less.
When the solid content concentration b is 18% by mass or more, the polymer forms a fine granular structure by phase separation, and as a result, a dense layer is easily obtained. Further, when the solid content concentration b is 35% by mass or less, the surface pore diameter of the porous support layer is adjusted to such an extent that the monomer supply rate at the time of forming the separation functional layer does not become too small.
Therefore, a convex portion having an appropriate height can be formed on the separation functional layer formed on the porous support layer.
The preferred temperature, coating method, good solvent and non-solvent, coagulation bath conditions, additives, etc. of the polymer solution B are the same as those of the polymer solution A forming the first layer described above.

  When the solid content concentration a and the solid content concentration b satisfy the respective preferable numerical ranges described above, the porosity of the first layer is 60% or more and the porosity of the first layer is the porosity of the second layer. It is possible to make it higher. Further, if the thickness x of the first layer and the thickness y of the second layer satisfy the relational expression x / y ≧ 10, a pleat having both sufficient linear density and height can be formed in the separation functional layer, and the result It is preferable because a composite semipermeable membrane having sufficient water permeability and salt removability can be obtained. Further, the porosity of the first layer may be 62% or more. The porosity of the first layer is preferably 90% or less, and may be 80% or less, or 70% or less.

The resins contained in the polymer solution A and the polymer solution B may be the same resin or different resins. As appropriate, various characteristics such as strength characteristics, permeability characteristics, and surface characteristics of the support membrane to be manufactured can be prepared in a wider range.
In addition, the solvent contained in the polymer solution A and the polymer solution B may be the same solvent or different solvents as long as each is a good polymer solvent. As appropriate, it can be prepared in a wider range in consideration of the strength characteristics of the support membrane to be produced and the impregnation of the polymer solution into the substrate.

  Next, the support film including the base material and the porous support layer obtained under such preferable conditions is washed with hot water in order to remove the film-forming solvent remaining in the film. The temperature of the hot water at this time is preferably 50 to 100 ° C, more preferably 60 to 95 ° C. If it is higher than this range, the degree of shrinkage of the support membrane will increase and the water permeability will decrease. Conversely, if it is low, the cleaning effect is small.

(2-2) Formation process of separation functional layer Next, as an example of the formation process of the separation functional layer constituting the composite semipermeable membrane, formation of a layer mainly composed of polyamide will be described.
In the step of forming the polyamide separation functional layer, interfacial polycondensation is performed on the surface of the support membrane using the aqueous solution containing the polyfunctional amine described above and an organic solvent solution immiscible with water containing the polyfunctional acid halide. By doing so, a polyamide skeleton can be formed.

The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 3.0% by mass or more and 25% by mass or less, and more preferably in the range of 5.0% by mass or more and 20% by mass or less. Within this range, sufficient water permeability and salt and boron removal performance can be obtained, and at the same time, a polyamide having sufficient hardness can be formed.
As long as the polyfunctional amine aqueous solution does not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide, a surfactant, an organic solvent, an alkaline compound, an antioxidant, or the like may be contained.
The surfactant has the effect of improving the wettability of the support membrane surface and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and when added, the interfacial polycondensation reaction may be efficiently performed.

In order to perform the interfacial polycondensation on the support membrane, first, the polyfunctional amine aqueous solution is brought into contact with the support membrane. The contact is preferably performed uniformly and continuously on the support membrane surface.
Specific examples include a method of coating a polyfunctional amine aqueous solution on a support membrane and a method of immersing the support membrane in a polyfunctional amine aqueous solution. The contact time between the support membrane and the polyfunctional amine aqueous solution is preferably in the range of 5 seconds to 10 minutes, and more preferably in the range of 10 seconds to 3 minutes.

After bringing the polyfunctional amine aqueous solution into contact with the support membrane, the solution is sufficiently drained so that no droplets remain on the membrane. By sufficiently draining the liquid, it is possible to prevent the removal performance of the composite semipermeable membrane from being deteriorated due to the remaining portion of the droplet after the formation of the composite semipermeable membrane.
As a method for draining, for example, as described in JP-A-2-78428, a method of allowing the excess aqueous solution to flow down naturally by holding the support film after contacting the polyfunctional amine aqueous solution in the vertical direction, For example, a method of forcibly draining an air stream such as nitrogen from an air nozzle can be used. In addition, after draining, the membrane surface can be dried to partially remove water from the aqueous solution.

  Next, the support membrane after contacting and draining the polyfunctional amine aqueous solution is brought into contact with water containing a polyfunctional acid halide and an immiscible organic solvent solution to form a crosslinked polyamide separation functional layer by interfacial polycondensation.

  The concentration of the polyfunctional acid halide in the organic solvent solution immiscible with water is preferably in the range of 0.15% by mass to 10% by mass, preferably 0.16% by mass to 2.0% by mass. More preferably within the range. When the polyfunctional acid halide concentration is 0.15% by mass or more, a sufficient reaction rate can be obtained, and when it is 10% by mass or less, the occurrence of side reactions can be suppressed. Further, it is more preferable to include an acylation catalyst such as DMF in the organic solvent solution, since interfacial polycondensation is promoted.

The water-immiscible organic solvent is preferably one that dissolves the polyfunctional acid halide and does not destroy the support membrane, and may be any one that is inert to the polyfunctional amine compound and polyfunctional acid halide. . Preferable examples include hydrocarbon compounds such as hexane, heptane, octane, nonane and decane.
The method of bringing the organic solvent solution containing the polyfunctional acid halide into contact with the support membrane may be performed in the same manner as the method of coating the support membrane with the polyfunctional amine aqueous solution.

In the interfacial polycondensation step of the present invention, the support membrane is sufficiently covered with a crosslinked polyamide thin film, and a water-immiscible organic solvent solution containing a polyfunctional acid halide in contact with the support membrane is left on the support membrane. It is important to keep it. For this reason, the time for performing the interfacial polycondensation is preferably from 0.1 second to 3 minutes, and more preferably from 0.1 second to 1 minute.
When the interfacial polycondensation time is 0.1 seconds or more and 3 minutes or less, the support membrane can be sufficiently covered with a crosslinked polyamide thin film, and an organic solvent solution containing a polyfunctional acid halide is supported on the support membrane. Can be held on.

After the polyamide separation functional layer is formed on the support membrane by interfacial polycondensation, excess solvent is drained. As a method for draining, for example, a method in which a film is held in a vertical direction and excess organic solvent is allowed to flow down and removed can be used.
In this case, the time for gripping in the vertical direction is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. If it is too short, the separation functional layer will not be completely formed, and if it is too long, the organic solvent will be overdried and a defective part will occur in the polyamide separation functional layer, resulting in poor membrane performance.

3. Use of composite semipermeable membranes Composite semipermeable membranes have a large number of holes along with raw water channel materials such as plastic nets, permeate channel materials such as tricots, and films to increase pressure resistance as needed. It is wound around a cylindrical water collecting pipe and is suitably used as a spiral type composite semipermeable membrane element. Further, this element can be connected in series or in parallel and housed in a pressure vessel to constitute a composite semipermeable membrane module.
In addition, the above-described composite semipermeable membrane and its elements or modules can be combined with a pump for supplying raw water to them, a device for pretreating the raw water, or the like to constitute a fluid separation device. By using this separation device, raw water can be separated into permeated water such as drinking water and concentrated water that has not permeated through the membrane, and water suitable for the purpose can be obtained.

The higher the operating pressure of the fluid separator, the better the salt removal, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, water to be treated is added to the composite semipermeable membrane. The operating pressure at the time of permeation is preferably 1.0 MPa or more and 10 MPa or less.
As the feed water temperature increases, the salt removability decreases, but the membrane permeation flux decreases as the supply water temperature decreases, so that the feed water temperature is preferably 5 ° C. or higher and 45 ° C. or lower. In addition, when the pH of the feed water becomes high, scales such as magnesium may be generated in the case of feed water with a high salt concentration such as seawater, and there is a concern about deterioration of the membrane due to high pH operation. Is preferred.

Examples of raw water to be treated by the composite semipermeable membrane include liquid mixtures containing TDS (Total Dissolved Solids) of 500 mg / L to 100 g / L such as seawater, brine, and drainage. Generally, TDS refers to the total amount of dissolved solids and is expressed as “mass / volume” or expressed as “mass ratio” assuming that the weight of 1 L is 1 kg.
According to the definition, the TDS can be calculated from the weight of the residue by evaporating the solution filtered through a 0.45 μm filter at a temperature of 39.5 to 40.5 ° C. To do.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

<Production of composite semipermeable membrane>
In the following examples, polysulfone UDEL p-3500 manufactured by Solvay Advanced Polymers Co., Ltd. was used as the polysulfone.
Example 1
A mixture of DMF as a solvent and polysulfone as a solute was heated and held at 90 ° C. for 2 hours with stirring to prepare a DMF solution (polymer solution A) containing 13% by mass of polysulfone. The prepared polymer solution A was cooled to room temperature, supplied to an extruder and filtered with high precision. Thereafter, the filtered polymer solution A was placed on a long-fiber nonwoven fabric made of polyethylene terephthalate fibers (yarn diameter: 1 dtex, thickness: about 90 μm, air permeability: 1.3 cc / cm ² / sec) through a slit die to 100 μm. The first layer of the porous support layer was produced by immediately applying immersion in pure water.
Subsequently, a 20% by weight polysulfone DMF solution (polymer solution B) was prepared and filtered by the same method as described above, applied to a smooth glass substrate with a thickness of 10 μm via a slit die, and immediately purified water. Soaked. Thereafter, the glass substrate and the polysulfone layer were separated, and the polysulfone layer was pressure-bonded after applying heat at 70 ° C. to the surface of the first layer to obtain a support film including a two-layer porous support layer. The obtained support membrane was washed with 70 ° C. water for 2 minutes.
The washed support membrane was immersed in a 4.0% by mass aqueous solution of m-PDA for 2 minutes, and then slowly lifted so that the membrane surface was vertical. Nitrogen was blown from the air nozzle to remove excess aqueous solution from the surface of the support film, and then an n-decane solution at 25 ° C. containing 0.12% by mass of trimesic acid chloride was applied so that the film surface was completely wetted. After leaving still for 1 minute, in order to remove excess solution from the film, the film surface was held vertically for 1 minute to drain the liquid. Then, the composite semipermeable membrane provided with a base material, a porous support layer, and a polyamide separation functional layer was obtained by washing with water at 45 ° C. for 2 minutes.

(Example 2)
In Example 1, a composite semipermeable membrane in Example 2 was obtained in the same manner as in Example 1 except that the polymer solution A was coated with a DMF solution containing 15% by mass of polysulfone to a thickness of 110 μm.
(Example 3)
In the same manner as in Example 1, except that the polymer solution A was applied in a thickness of 120 μm and the polymer solution B was applied in a thickness of 5 μm using a DMF solution of 25% by weight of polysulfone as the polymer solution B. A composite semipermeable membrane in Example 3 was obtained.
Example 4
In Example 1, except that an NMP solution containing 13% by mass of polysulfone was used as the polymer solution A and an NMP solution containing 20% by mass of polysulfone was used as the polymer solution B, the composite in Example 4 was used. A semipermeable membrane was obtained.

(Comparative Example 1)
A composite semipermeable membrane in Comparative Example 1 was obtained in the same manner as in Example 1 except that the polymer solution A was applied in a thickness of 90 μm in Example 1.
(Comparative Example 2)
A composite semipermeable membrane in Comparative Example 2 was obtained in the same manner as in Example 1 except that the polymer solution A was applied with a thickness of 150 μm and the polymer solution B was applied with a thickness of 15 μm.
(Comparative Example 3)
A single porous support membrane was obtained by the same procedure as in Example 1 except that only 20% by weight DMF solution of polysulfone was applied on the nonwoven fabric with a thickness of 120 μm using a slit die. A separation functional layer was formed on the obtained porous support membrane by the same procedure as in Example 1, and a composite semipermeable membrane in Comparative Example 1 was obtained.
(Comparative Example 4)
A composite semipermeable membrane in Comparative Example 4 was obtained in the same manner as in Comparative Example 3, except that a DMF solution containing 13% by weight of polysulfone was used as the polymer solution.

<Measurement of thickness of porous support layer>
About the obtained composite support membrane sample, the cross-sectional photograph was image | photographed using the digital microscope VHX-1000 by Keyence. The observation magnification at this time was 100 times. About 30 arbitrary places of the obtained cross-sectional photograph, the thickness of each support layer was measured with the scale, and average thickness was calculated | required.
The same operation was carried out for a total of 10 composite semipermeable membrane samples, and the average thickness was determined by arithmetic mean from the 10 thickness values.

<Measurement of linear density and average height of protrusions>
The obtained composite semipermeable membrane sample was embedded with an epoxy resin and stained with osmium tetroxide for easy cross-sectional observation. This was cut with an ultramicrotome to prepare an ultrathin section.
A cross-sectional photograph of the obtained ultrathin slice was taken using a transmission electron microscope. The acceleration voltage at the time of observation was 100 kV, and the observation magnification was 10,000 times. About the obtained cross-sectional photograph, the number of convex portions of the separation functional layer at a distance of 2.0 μm in the film surface direction was measured using a scale, and the 10-point average surface roughness was calculated according to the method described above. Based on this 10-point average surface roughness, a portion having a height of 1/5 or more of the 10-point average surface roughness is defined as a convex portion, and the number thereof is counted to obtain the linear density of the convex portion of the separation function layer. It was. Moreover, the height of all the convex parts in a cross-sectional photograph was measured with the scale, and the average height of the convex parts was obtained.
The same operation was performed for a total of 10 ultrathin sections, and the average linear density by arithmetic mean was determined from the values of the 10 linear densities. Further, an arithmetic average value of 10 average heights was obtained.

<Measurement of porosity of first layer of porous support layer>
Composite semipermeable membrane samples were embedded with epoxy resin and stained with osmium tetroxide to facilitate cross-sectional observation. Subsequently, etching of the sample with an ion beam and cross-sectional observation were repeated 200 times using FIB-SEM. From the obtained cross-sectional photograph, a three-dimensional image having a thickness of about 2 μm in the depth direction was reconstructed. Image analysis of this three-dimensional image was performed, and the porosity of the first layer portion of the porous support layer was calculated.
The polysulfone concentration of the polymer solution forming the second layer (shown as “polymer concentration” in Table 1) is higher than the polysulfone concentration of the polymer solution forming the first layer. It can be estimated that the porosity of the two layers is lower than the porosity of the first layer.

<Salt removability (TDS removal rate)>
Seawater (corresponding to feed water) at a temperature of 25 ° C. and a pH of 6.5 was supplied to a composite semipermeable membrane obtained at an operating pressure of 5.5 MPa, and subjected to filtration treatment for 24 hours. The obtained permeated water was used for the measurement of salt removability.
Practical salinity was obtained by measuring the electrical conductivity of the supplied water and the permeated water with an electric conductivity meter manufactured by Toa Radio Industry Co., Ltd. From the TDS concentration obtained by converting this practical salinity, the salt removability, that is, the TDS removal rate was determined by the following equation.
TDS removal rate (%) = 100 × {1− (TDS concentration in permeated water / TDS concentration in feed water)}

<Membrane permeation flux>
The amount of permeated water obtained by the above filtration treatment for 24 hours was expressed as a membrane permeation flux (m ³ / m ² / day) with a water permeation amount per cubic meter (m ³ ) per day.

  The results of Examples 1 to 4 and Comparative Examples 1 to 4 are shown in Table 1. Note that the linear density and average height of the convex portions of the separation functional layer are shown as “folded line density” and “folded height” in Table 1, respectively. From Examples 1-4, it turned out that the composite semipermeable membrane which has high water permeability is obtained by this invention, maintaining a high TDS removal rate.

  The composite semipermeable membrane of the present invention can be particularly suitably used for brine or seawater desalination.

DESCRIPTION OF SYMBOLS 1 Separation functional layer 2 Reference line H1, H2, H3, H4, H5 Height of convex part in pleat structure of separation functional layer D1, D2, D3, D4, D5 Depth of concave part in pleat structure of separation functional layer

Claims (6)

A substrate;
A porous support layer provided on the substrate;
A separation semi-permeable membrane provided on the porous support layer and having a pleated structure including convex and concave portions that are continuously repeated on the surface;
The porous support layer has a multilayer structure including a first layer and a second layer present on the separation function layer side of the first layer;
The thickness x (μm) of the first layer and the thickness y (μm) of the second layer satisfy the relational expression (x / y) ≧ 10,
The second layer has a thickness of 10 μm or less;
The porosity of the first layer is higher than the porosity of the second layer, and
A composite semipermeable membrane, wherein the porosity of the first layer is 60% or more.   The composite semipermeable membrane according to claim 1, wherein the thickness of the second layer is 5 μm or less.   The composite semipermeable membrane according to claim 1 or 2, wherein a standard deviation of the thickness of the second layer is 1.0 µm or less.   The composite semipermeable membrane according to any one of claims 1 to 3, wherein the second layer contains fine particles. Select arbitrarily 10 cross-sections with a length of 2.0 μm in the membrane surface direction of the composite semipermeable membrane,
Observe each cross section with an electron microscope to measure the 10-point average surface roughness in the separation functional layer,
Obtain the linear density of the convex portion having a height of 1/5 or more of the 10-point average surface roughness,
The average of the linear density obtained at the 10 locations is 12.0 pieces / μm or more, and
Obtain the average height of the convex portion having a height of 1/5 or more of the 10-point average surface roughness,
The composite semipermeable membrane according to any one of claims 1 to 4, wherein an average of the average heights obtained at the 10 locations is 110 nm or more.   The composite semipermeable membrane according to any one of claims 1 to 5, wherein the base material is a long-fiber nonwoven fabric containing polyester.

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