Composite semipermeable membrane and method for producing same

Abstract

The present invention provides a composite semipermeable membrane comprising a porous support layer and a separation functional layer located on the porous support layer, the composite semipermeable membrane having a first surface that is a surface positioned on the separation functional layer side and a second surface that is a surface positioned on the opposite side to the first surface, in which the separation functional layer contains a crosslinked polyamide, and the amino group density measured with a scanning transmission electron microscope (STEM) in a cross section taken in the thickness direction of the separation functional layer satisfies the formula: Nb / Nd ≤ 0.40 (wherein Nb and Nd are defined in the description).　

Description

Composite semipermeable membrane and method for producing the same

[0001] The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture. The composite semipermeable membrane obtained by the present invention can be suitably used, for example, for desalination of seawater or brackish water.

[0002] Regarding the separation of mixtures, there are various techniques for removing substances (e.g., salts) dissolved in a solvent (e.g., water). In recent years, membrane separation has been increasingly used as an energy- and resource-saving process.

[0003] Membranes used in membrane separation include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes are used, for example, to obtain drinking water from seawater, brackish water, or water containing harmful substances, to produce ultrapure water for industrial use, to treat wastewater, and to recover valuable resources.

[0004] Patent Document 1 discloses a composite semipermeable membrane having a porous support membrane and a separation functional layer made of crosslinked polyamide coated thereon, as a separation membrane with high water permeability and removal properties. The separation functional layer is formed on the porous support membrane by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide.

[0005] Japanese Patent Application Publication No. 2001-79372

[0006] However, due to the increasing need for energy saving during operation, the permeability of composite semipermeable membranes must be further increased compared to conventional membranes. However, increasing the permeability of composite semipermeable membranes also leads to a problem of a corresponding decrease in removal efficiency.

[0007] Therefore, an object of the present invention is to provide a composite semipermeable membrane that is excellent in water permeability and removal properties.

[0008] The present invention for solving the above problems includes the following configurations [1] to

[11] . [1] A composite semipermeable membrane comprising a porous support layer and a separation functional layer located on the porous support layer, wherein the composite semipermeable membrane comprises a first surface on the separation functional layer side and a second surface opposite to the first surface, the separation functional layer contains a crosslinked polyamide, and the amino group density measured by scanning transmission electron microscopy (STEM) in a cross section in the thickness direction of the separation functional layer satisfies Nb / Nd≦0.40. Nb: amino group density of region b Nd: amino group density of region d Regions a to e: regions obtained by dividing the cross section into five equal parts in the thickness direction of the separation functional layer, and regions a to e are aligned from the first surface toward the second surface. [2] The Nb is 1.0×10 －２４ mol / nm ２ or less, and the Nd is 2.5 × 10 －２４ mol / nm ２ [3] The composite semipermeable membrane according to [1] above, wherein, when the amount of terminal amino groups in the crosslinked polyamide is A, the amount of terminal carboxyl groups is B, and the amount of amide groups is C, C / (A+B) is 1.7 or more. [4] The composite semipermeable membrane according to any of [1] to [3] above, wherein the separating functional layer has a thin film containing a crosslinked polyamide as a main component, and the thickness of the thin film is 9.0 nm or more and 13.0 nm or less. [5] The composite semipermeable membrane according to any of [1] to [4] above, wherein, when water containing 500 ppm of sodium chloride, 20 ppm of silica, and 1 ppm of boron is permeated through the composite semipermeable membrane at an operating pressure of 0.75 MPa, the following formulas (1) to (5) are satisfied: Silica removal rate ≧ 99.30% Equation (1) Boron removal rate ≧ 60% Equation (2) Permeate volume ≧ 0.85 m ３ / m ２ / day Equation (3) 99.90% > NaCl rejection rate ≧ 99.50% Equation (4) (NaCl rejection rate) − (silica rejection rate) ≦ 0.20% Equation (5) [6] A method for producing a composite semipermeable membrane, comprising contacting a polyfunctional amine solution containing compound X with a polyfunctional acid halide solution containing compound Y on a porous support layer to form a polyamide layer by an interfacial polycondensation reaction, wherein the octanol / water partition coefficients of compound X and compound Y satisfy the following equations (6) to (8): Log P(X) < 0 Equation (6) Log P(Y) < 0 Equation (7) Log P(X) / Log P(Y) < 0.50 Equation (8) [7] A method for producing the composite semipermeable membrane according to [6] above, wherein the water content of the organic solvent in which the polyfunctional acid halide is dissolved is 50 ppm or less. [8] On the porous support layer, the polyfunctional amine solution and a solution of 200 mL / m2 of the surface area of ​​the porous support layer are added. ２ More than 400mL / m ２ a polyfunctional acid halide solution in an amount of 0.1 to 0.5% by weight, and a polyamide layer is formed by an interfacial polycondensation reaction. [9] A method for producing ultrapure water, comprising a reverse osmosis step of removing silica from a silica-containing aqueous solution using the composite semipermeable membrane of any of [1] to [5] above.

[10] The method for producing ultrapure water according to [9] above, further comprising a pretreatment step of removing suspended matter from the silica-containing aqueous solution before the reverse osmosis step.

[11] The method for producing ultrapure water according to [9] or

[10] above, further comprising a step of removing solute salts using an ion exchange resin from the aqueous solution treated in the reverse osmosis step.

[12] A composite semipermeable membrane element comprising the composite semipermeable membrane according to any of [1] to [5] above.

[13] A composite semipermeable membrane module comprising the composite semipermeable membrane element according to

[12] above.

[0009] The composite semipermeable membrane of the present invention can form a surface pore size sufficient for removing solutes while suppressing the resistance to water permeation by providing a gradient in amino group density in the thickness direction of the separation functional layer, thereby achieving both high water permeability and high removability.

[0010] Fig. 1 is a cross-sectional view showing the schematic configuration of a composite semipermeable membrane according to one embodiment of the present invention. Fig. 2 is a cross-sectional view showing the pleated structure of a thin film in a separation functional layer. Fig. 3 is a schematic view explaining a method for measuring 10-point average surface roughness. Fig. 4 is a cross-sectional view showing regions a to e in a thin film in a separation functional layer. Fig. 5 is a flow chart showing the steps of a method for producing ultrapure water according to one embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto. In this specification, "mass" has the same meaning as "weight."

[0012] (1) Composite semipermeable membrane The composite semipermeable membrane of the present invention comprises a porous support layer and a separation functional layer located on the porous support layer. As shown in Figure 1, in this embodiment, the surface of the composite semipermeable membrane 1 facing the separation functional layer 4 is called the first surface 11, and the surface opposite to the first surface is called the second surface 12.

[0013] (1-1) Separation Functional Layer (1-1-1) Composition Among the components of a composite semipermeable membrane, it is the separation functional layer that substantially has the ability to separate solutes. In the cross-sectional view of the composite semipermeable membrane shown in Figure 1, the separation functional layer 4 is disposed on the porous support layer 3. The separation functional layer contains a crosslinked polyamide, and preferably contains a crosslinked polyamide as the main component. In this specification, "X contains Y as the main component" means that Y comprises 50% by mass or more, 80% by mass or more, or 90% by mass or more of X, and also includes the case where X is composed of Y alone.

[0014] The crosslinked polyamide refers to a polycondensation product of a polyfunctional amine and a polyfunctional acid halide. Here, the term "polyfunctional amine" refers to an amine having at least two primary amino groups and / or secondary amino groups per molecule, at least one of which is a primary amino group. Examples of polyfunctional amines include polyfunctional aromatic amines such as phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine, in which two amino groups are bonded to a benzene ring at the ortho, meta, or para positions; aliphatic amines such as ethylenediamine and propylenediamine; and alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, and 4-aminoethylpiperazine.

[0015] In particular, in consideration of the selectivity, permeability, and heat resistance of the composite semipermeable membrane, the polyfunctional amine is preferably a polyfunctional aromatic amine having two to four primary amino groups and / or secondary amino groups in one molecule. Suitable examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene. Of these, m-phenylenediamine (hereinafter referred to as "m-PDA") is more preferably used because of its ease of availability and ease of handling.

[0016] These polyfunctional amines may be used alone or in combination of two or more. When two or more types are used in combination, the above amines may be combined with each other, or the above amine may be combined with an amine having at least two secondary amino groups in one molecule. Examples of amines having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidylpropane.

[0017] The polyfunctional acid halide refers to an acid halide having at least two halocarbonyl groups in one molecule. Examples of trifunctional acid halides include trimesoyl chloride (hereinafter referred to as "TMC"), 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride.

[0018] Examples of the bifunctional acid halides include aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic bifunctional acid halides such as adipoyl chloride and sebacoyl chloride; and alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride.

[0019] Considering the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride. Furthermore, considering the selectivity and heat resistance of the composite semipermeable membrane, the polyfunctional acid halide is more preferably a polyfunctional aromatic acid chloride having two to four carbonyl chloride groups per molecule. Among these, trimesoyl chloride is more preferred from the viewpoints of availability and ease of handling. These polyfunctional acid halides may be used alone or in combination of two or more.

[0020] The separation functional layer preferably has a thin film with a pleated structure. This thin film preferably contains crosslinked polyamide as a main component. From the viewpoint of obtaining sufficient separation performance and permeation rate, the thickness of the thin film is preferably 8.0 nm or more, more preferably 9.0 nm or more. On the other hand, the thickness of the thin film is preferably 20.0 nm or less, more preferably 13.0 nm or less.

[0021] The thickness of the pleated thin film can be controlled, for example, by the concentration of the polyfunctional amine and polyfunctional acid halide monomers, and the amount of polyfunctional acid halide solution applied relative to the surface area of ​​the porous support layer, as described below in the "Separation Functional Layer Formation Process."

[0022] The thickness of the thin film can be measured by photographing a cross section of the pleated thin film using a transmission electron microscope (hereinafter referred to as "TEM") and then importing the cross-sectional photograph into image analysis software for analysis. Specifically, in a TEM image of the cross section of the separation functional layer, any five convex portions formed by the thin film are selected. For one convex portion (reference numerals 21 and 22 in Figure 2), the thickness of the thin film (reference numeral 27 in Figure 2) is measured at 10 points within a region extending from the apex of the convex portion to 90% of the height (reference numerals 23 and 24 in Figure 2). In other words, as shown in Figure 2, the surface of the porous support layer is at 0% height, the apex of the convex portion is at 100% height, and 10 measurement points are selected arbitrarily within the range of 10 to 100% height. The arithmetic mean value calculated from the thicknesses at a total of 50 points thus obtained is the "thickness of the thin film."

[0023] Here, the convex portions to be measured when calculating the thickness of the thin film are convex portions having a height equal to or greater than one-fifth of the 10-point average surface roughness.

[0024] The 10-point average surface roughness is calculated as follows. First, a cross section perpendicular to the film surface is observed using an electron microscope. The magnification is preferably 10,000 to 100,000 times. In the obtained cross-sectional image, the surface of the separation functional layer 4 appears as a pleated curve with continuously repeated convex and concave portions, as shown in FIG. 3 . A roughness curve defined in accordance with JIS B 0601:2013 (ISO 4287:1997) is obtained for this curve. A section of the cross-sectional image with a width of 2.0 μm is extracted from the cross-sectional image, with a reference length L in the direction of the mean line X of the roughness curve. From this extracted section, the average of the absolute values ​​of the elevations of the highest to fifth peaks (Yp1 to Yp5) and the lowest to fifth valleys (Yv1 to Yv5) on the roughness curve is calculated. This value, expressed in nanometers (nm), is the 10-point average surface roughness (FIG. 3).

[0025] The mean line is a straight line defined in accordance with ISO 4287:1997, and refers to a straight line drawn so that the total area of ​​the region enclosed by the mean line and the roughness curve over the measurement length is equal above and below the mean line.

[0026] In this embodiment, the median height of the convex portions of the separation functional layer is preferably 80 nm or more, more preferably 120 nm or more, and even more preferably 160 nm or more, from the viewpoint of obtaining a sufficient amount of permeated water. On the other hand, the median height of the convex portions of the separation functional layer is preferably 300 nm or less.

[0027] The median height of the convex portions is calculated as follows. When 10 arbitrary cross sections of the composite semipermeable membrane are observed, the height of the convex portions that is at least one-fifth of the above-mentioned 10-point average surface roughness is measured at each cross section. Furthermore, the median height of the convex portions can be determined by calculating the median value based on the calculation results for the 10 cross sections. Here, each cross section has a width of 2.0 μm in the direction of the mean line of the roughness curve.

[0028] The term "protrusion" refers to the space between the apexes of adjacent portions (recesses) of the thin film of the separation functional layer that protrude toward the porous support layer. As shown in Figure 2, one of the ends of the protrusion (the apex of the recess) may be separated from the surface of the porous support layer and the other may be in contact with the surface of the porous support layer, or both ends may be in contact with the porous support layer, or both ends may be separated.

[0029] The height of the convex portions of the separation functional layer can be controlled by adjusting the diffusibility of the polyfunctional amine into the organic layer, for example, by adding an additive that interacts with the polyfunctional amine through hydrogen bonding or the like to the aqueous layer or organic layer.

[0030] (1-1-2) Characteristics In the composite semipermeable membrane of the present invention, the amino group density measured by a scanning transmission electron microscope (hereinafter referred to as "STEM") in a cross section in the thickness direction of the separation functional layer (cross section perpendicular to the first surface) satisfies Nb / Nd≦0.40. Here, Nb means the amino group density of region b, and Nd means the amino group density of region d. Furthermore, as shown in FIG. 4, each region is obtained by dividing the cross section in the thickness direction of the separation functional layer into five equal parts, and is arranged in the order of regions a to e from the first surface to the second surface.

[0031] The separation functional layer, which is primarily composed of crosslinked polyamide formed by interfacial polycondensation, has amino and carboxyl groups as terminal functional groups. In regions with high amino group density, the separation functional layer has a sparse structure, resulting in low water resistance and high water permeability, but insufficient solute removal performance. On the other hand, in regions with low amino group density, the separation functional layer has a dense structure, resulting in high water resistance and low water permeability, but high solute removal performance.

[0032] The present inventors have found that a separation functional layer having a gradient structure of amino group density satisfying Nb / Nd≦0.40 can achieve both particularly high water permeability and removal performance. From the viewpoint of achieving both water permeability and removal performance, Nb / Nd is preferably 0.05 or more, more preferably 0.10 or more. On the other hand, Nb / Nd is preferably 0.35 or less, more preferably 0.30 or less.

[0033] As described in the "Separation functional layer formation process" below, Nb / Nd can be controlled, for example, by the type and concentration of compound X contained in the polyfunctional amine solution or compound Y contained in the polyfunctional acid halide solution, the water content contained in the organic solvent that dissolves the polyfunctional acid halide, and the amount of polyfunctional acid chloride solution applied relative to the surface area of ​​the porous support layer.

[0034] (i) Each region a to e of the separation functional layer: The composite semipermeable membrane is immersed in an aqueous solution of sodium tungstate (IV) for 7 minutes, and this process is repeated four times. A cross section of the separation functional layer in this composite semipermeable membrane is photographed at 100,000 magnification using an STEM. In the obtained image, in any region of each convex portion of the separation functional layer (thin film) that is within 50 to 100% of its height, a reference point P is determined on the outer surface 26 of the thin film (the surface facing away from the porous support layer), and lines V1 and V2 parallel to the normal line V0 are drawn on both sides of the reference point P, with a normal line V0 passing through the reference point P as the center, at an interval of 3 to 10 nm. A tangent line Z1 to the outer surface of the thin film passing through the reference point P is drawn, and a tangent line Z2 parallel to the tangent line Z1 to the inner surface 25 of the thin film (the surface in contact with the porous support layer) is drawn. Four lines are drawn between Z1 and Z2, dividing this interval into five equal parts. The regions surrounded by V1 and V2, and also surrounded by Z1, Z2 and the straight line between them, are designated as regions a to e in order from the outer surface side of the thin film (Figure 4). The area of ​​each of regions a to e is 5 nm ２30nm or more ２ The following applies.

[0035] (ii) Amino group density The brightness is measured by STEM in the above-mentioned regions a to e. The area of ​​the portion showing a brightness of {Lmin + (Lmax - Lmin) / 3} or more is integrated for each region, where the minimum brightness Lmin and maximum brightness Lmax of the measured values ​​are the minimum brightness Lmin and the maximum brightness Lmax. This integrated value means the area of ​​the portion having amino groups labeled with tungsten (W). The obtained integrated value is calculated as the area per amino group molecule (0.04 nm ２ ), Avogadro's constant (6.0 x 10 ２３ The amino group density (mol / nm) was calculated by dividing the area of ​​each region by the number of amino groups / mol. ２ The average value of the amino group densities obtained for five convex portions of the thin film is taken as the amino group density of each region.

[0036] The composite semipermeable membrane of the present embodiment has an Nb content of 1.0 × 10 －２４ mol / nm ２ or less, and Nd is 2.5 × 10 －２４ mol / nm ２ A membrane having a low amino group density near the surface has a polyamide structure dense enough to be suitable for removing solutes, and from the viewpoint of improving the removability of the membrane, Nb is preferably 0.8 × 10 －２４ mol / nm ２ More preferably, 0.6×10 or less －２４ mol / nm ２ On the other hand, from the viewpoint of ensuring the water permeability of the membrane, Nb is more preferably 0.2 × 10 －２４ mol / nm ２ More than 0.4 × 10 is preferable. －２４ mol / nm ２ Furthermore, in a membrane with a high amino group density on the inner layer side of the separating functional layer, the polyamide structure is sparse enough to reduce the water permeation resistance, and from the viewpoint of improving the water permeability of the membrane, Nd is 2.7 × 10 －２４ mol / nm ２ More preferably, 3.0 × 10 －２４ mol / nm ２On the other hand, from the viewpoint of maintaining the physical strength of the functional layer, Nd is 3.5×10 －２４ mol / nm ２ Preferably, the value is 3.0 x 10 or less. －２４ mol / nm ２ The following is more preferred:

[0037] As described in the "Separation functional layer formation process" below, Nb and Nd can be controlled, for example, by the type and concentration of compound X contained in the polyfunctional amine solution or compound Y contained in the polyfunctional acid halide solution, the water content contained in the organic solvent that dissolves the polyfunctional acid halide, and the amount of polyfunctional acid chloride solution applied relative to the surface area of ​​the porous support layer.

[0038] (iii) Amount A of Terminal Amino Groups, Amount B of Terminal Carboxy Groups, and Amount C of Amide Groups of Crosslinked Polyamide The amount A of terminal amino groups, the amount B of terminal carboxy groups, and the amount C of amide groups of the crosslinked polyamide in the composite semipermeable membrane are determined by the amount A of terminal amino groups, the amount B of terminal carboxy groups, and the amount C of amide groups of the separating functional layer. １３ C solid-state nuclear magnetic resonance measurement (hereinafter referred to as “ １３ Specifically, the substrate is peeled off from the composite semipermeable membrane to obtain a separation functional layer and a porous support layer, and then the porous support layer is removed by dissolution to obtain the separation functional layer. The separation functional layer thus obtained is analyzed by DD / MAS method. １３ C solid state NMR measurement is carried out, and each ratio is calculated by comparing the integrated values ​​of the carbon peaks of each functional group or the carbon peaks to which each functional group is bonded.

[0039] From the viewpoint of improving the removal performance and physical strength, the composite semipermeable membrane of this embodiment preferably has a ratio (C / (A+B)) of the amount of amide groups C to the sum of the amount of terminal amino groups A and the amount of terminal carboxyl groups B of the crosslinked polyamide of 1.7 or more. C / (A+B) means the ratio of amide groups to the amount of terminal groups of the crosslinked polyamide. A relatively large amount of amide groups, which are crosslinking points, improves the density of the membrane, and increases the solute removal ability and the chemical and physical strength of the separating functional layer. For the above reasons, C / (A+B) is more preferably 1.8 or more, and even more preferably 1.9 or more. On the other hand, from the viewpoint of ensuring water permeability, C / (A+B) is preferably 2.2 or less, and more preferably 2.1 or less.

[0040] The amount A of terminal amino groups, the amount B of terminal carboxyl groups, and the amount C of amide groups of the crosslinked polyamide can be controlled, for example, by the concentrations of the polyfunctional amine and polyfunctional acid halide monomers or the polymerization time.

[0041] (iv) Separation Characteristics The composite semipermeable membrane of this embodiment is suitable for separating nonionic solutes as well as ionic solutes such as sodium chloride, and is characterized by differences in the removal efficiency of each solute.

[0042] The composite semipermeable membrane of this embodiment preferably has a silica removal rate of 99.30% or more, more preferably 99.45% or more, when feed water containing 500 ppm sodium chloride (hereinafter referred to as "NaCl"), 20 ppm nonionic silica, and 1 ppm boron is passed through it at an operating pressure of 0.75 MPa. The boron removal rate is preferably 60% or more, more preferably 65% ​​or more. The NaCl removal rate is preferably 99.50% or more, more preferably 99.60% or more, and preferably less than 99.90%. In addition, the difference between the NaCl removal rate and the silica removal rate is preferably 0.20% or less. When the silica removal rate, boron removal rate, NaCl removal rate, and the difference between the NaCl removal rate and the silica removal rate are within the above ranges, high-quality permeate water can be obtained while suppressing the concentration of solutes such as scale on the membrane surface.

[0043] Here, the removal rate of each solute is expressed as 100×{1−(solute concentration in permeate water / solute concentration in feed water)}.

[0044] In addition, from the viewpoint of reducing the energy consumption during membrane operation, the permeate volume under the above conditions is set to 0.85 m ３ / m ２ It is preferable that the number of days is 1 or more.

[0045] (1-2) Porous Support Layer The porous support layer serves as a base for forming the separation functional layer, and does not itself have substantial separation performance for ions and the like.

[0046] The size and distribution of the pores in the porous support layer are preferably, for example, uniform and fine pores or pores that gradually become larger from the surface on which the separation functional layer is formed to the other surface, and the size of the pores on the surface on which the separation functional layer is formed is 0.1 nm or more and 100 nm or less.

[0047] The porous support layer can be obtained, for example, by casting a high molecular weight polymer onto a substrate that is a fabric made of at least one material selected from polyester and aromatic polyamide. The composite semipermeable membrane of this embodiment may include a porous support layer and a separation functional layer, but may also include a substrate 2 and a porous support layer 3 disposed on the substrate 2, as shown in Figure 1. Hereinafter, a configuration in which a porous support layer is formed on a substrate may be referred to as a "support membrane."

[0048] Examples of materials for the porous support layer include homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose-based polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide, either alone or in blends. Examples of cellulose-based polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile. Among these, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferred for the porous support layer. Cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone are more preferred. Among these materials, polysulfone is generally preferred due to its high chemical, mechanical, and thermal stability and ease of molding.

[0049] For example, a support membrane can be obtained by casting a polysulfone solution in N,N-dimethylformamide (hereinafter referred to as "DMF") to a certain thickness on a tightly woven polyester fabric or a polyester nonwoven fabric, and then wet-coagulating the cast membrane in water, whereby most of the surface has fine pores with diameters of several tens of nanometers or less.

[0050] The thickness of the support membrane affects the strength of the resulting composite semipermeable membrane and the packing density when it is made into an element. From the viewpoint of obtaining sufficient mechanical strength and packing density, the thickness of the support membrane is preferably 30 μm or more, more preferably 100 μm or more. On the other hand, the thickness of the support membrane is preferably 300 μm or less, more preferably 220 μm or less.

[0051] The morphology of the porous support layer can be observed using a scanning electron microscope, a transmission electron microscope, or an atomic force microscope. For example, when observing using a scanning electron microscope, the porous support layer peeled from the substrate is cut by freeze fracturing to obtain a sample for cross-sectional observation. This sample is thinly coated with platinum, platinum-palladium, or ruthenium tetrachloride and observed using a high-resolution field emission scanning electron microscope (hereinafter referred to as "UHR-FE-SEM") at an accelerating voltage of 3 to 15 kV. For the UHR-FE-SEM, an S-900 electron microscope manufactured by Hitachi, Ltd. or the like can be used.

[0052] The thickness of the porous support layer is preferably 20 μm or more and 100 μm or less. By making the thickness of the porous support layer 20 μm or more, good pressure resistance can be obtained and a uniform support membrane without any defects can be obtained. A composite semipermeable membrane including such a porous support layer exhibits good salt removal performance. Furthermore, by making the thickness of the porous support layer 100 μm or less, the amount of unreacted substances remaining during production can be reduced, and a decrease in the amount of permeate water and a decrease in chemical resistance can be suppressed.

[0053] (2) Manufacturing Method (2-1) Porous Support Layer Forming Step The porous support layer forming step includes a step of applying a polymer solution to a substrate and a step of immersing the substrate with the applied solution in a coagulation bath to coagulate the polymer.

[0054] In the step of applying the polymer solution to the substrate, the polymer solution is prepared by dissolving the polymer, which is a component of the porous support layer, in a good solvent for the polymer.

[0055] The temperature of the polymer solution during application is preferably 10°C or higher and 60°C or lower, for example, when polysulfone is used as the polymer. If the temperature of the polymer solution is within this range, the polymer does not precipitate, and the polymer solution is sufficiently impregnated into the spaces between the fibers of the substrate and then solidified. As a result, the porous support layer is firmly bonded to the substrate due to the anchor effect, and a good support membrane can be obtained. The preferred temperature range of the polymer solution can be adjusted as appropriate depending on the type of polymer used, the desired solution viscosity, etc.

[0056] The time period from when the polymer solution is applied to the substrate until the substrate is immersed in the coagulation bath is preferably 0.1 seconds or more and 5 seconds or less. If the time period until the substrate is immersed in the coagulation bath is within this range, the organic solvent solution containing the polymer is sufficiently impregnated into the spaces between the fibers of the substrate and then solidified. The preferred range of the time period until the substrate is immersed in the coagulation bath can be appropriately adjusted depending on the type of polymer solution used, the desired solution viscosity, etc.

[0057] Water is generally used as the coagulation bath, but any other suitable solution may be used as long as it does not dissolve the polymers that are components of the porous support layer. The composition of the coagulation bath changes the membrane morphology of the resulting support membrane, which in turn changes the resulting composite semipermeable membrane. The temperature of the coagulation bath is preferably from -20°C to 100°C, more preferably from 10°C to 50°C. If the temperature of the coagulation bath is within this range, the vibration of the coagulation bath surface due to thermal motion will not be severe, and the smoothness of the membrane surface after membrane formation will be maintained. Furthermore, if the temperature is within this range, the coagulation rate will be appropriate, resulting in good membrane formability.

[0058] Next, the obtained support membrane is washed with hot water to remove the solvent remaining in the membrane. The temperature of the hot water is preferably 40°C or higher and 100°C or lower, more preferably 60°C or higher and 95°C or lower. If the hot water temperature is within this range, the shrinkage of the support membrane does not increase and the amount of permeated water is good. Furthermore, if the hot water temperature is within this range, a sufficient washing effect can be obtained.

[0059] (2-2) Step of Forming Separation Functional Layer The method for producing a composite semipermeable membrane of this embodiment is a method for producing a composite semipermeable membrane, which comprises contacting a polyfunctional amine solution containing compound X with a polyfunctional acid halide solution containing compound Y on a porous support layer to form a polyamide layer by an interfacial polycondensation reaction, wherein the octanol / water partition coefficients of compound X and compound Y satisfy the following formulas (6) to (8): Log P(X) < 0 (6) Log P(Y) < 0 (7) Log P(X) / Log P(Y) < 0.50 (8) Here, Log P(X) means the octanol / water partition coefficient of compound X, and Log P(Y) means the octanol / water partition coefficient of compound Y.

[0060] The preferred embodiments of the polyfunctional amine and polyfunctional acid halide are the same as those described above. Hereinafter, the process will be described taking as an example a case where a polyfunctional aromatic amine is used as the polyfunctional amine and a polyfunctional aromatic acid chloride is used as the polyfunctional acid halide.

[0061] The organic solvent for dissolving the polyfunctional aromatic acid chloride may be any solvent that is immiscible with water, does not destroy the support film, and does not inhibit the crosslinked aromatic polyamide production reaction. Typical examples include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. Considering the fact that these solvents do not destroy the ozone layer, are readily available, are easy to handle, and are safe to handle, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, and the like, alone or in combination, are preferred.

[0062] The aqueous solution containing the polyfunctional aromatic amine contains a compound X having an octanol / water partition coefficient of less than 0, and the organic solvent dissolving the polyfunctional aromatic acid chloride contains a compound Y having an octanol / water partition coefficient of less than 0, and the ratio of the octanol / water partition coefficients of compound X and compound Y, Log P(X) / Log P(Y), is less than 0.50. When Log P(X) / Log P(Y) satisfies this range, compound X and compound Y are mixed appropriately at the interface during polymerization, and an intermediate layer that promotes the polymerization reaction is stably formed, resulting in the formation of a polyamide separation function layer with high separation performance. On the other hand, when Log P(X) / Log P(Y) is 0.50 or more, it becomes difficult for either compound X or compound Y to migrate, making it difficult to form an intermediate layer that promotes the polymerization reaction, and making it difficult to form a polyamide separation function layer with high separation performance.

[0063] Examples of the compound X and the compound Y include compounds having a polyoxyalkylene structure, a fatty acid structure, an amide structure, an ether structure, a sulfo group, or a hydroxyl group.

[0064] Examples of the polyoxyalkylene structure include -(CH ２ CH ２ O) ｎ -, -(CH ２ CH ２ (CH ３ ) O) ｎ -, -(CH ２ CH ２ CH ２ O) ｎ -, -(CH ２ CH ２ CH ２ CH ２ O) ｎ - and others.

[0065] Examples of fatty acid structures include fatty acids having a long-chain aliphatic group, which may be either linear or branched, such as salts of stearic acid, oleic acid, lauric acid, and palmitic acid.

[0066] Examples of compounds having a sulfo group include salts of 1-hexanesulfonic acid, 1-octanesulfonic acid, 1-decanesulfonic acid, 1-dodecanesulfonic acid, perfluorobutanesulfonic acid, toluenesulfonic acid, cumenesulfonic acid, and octylbenzenesulfonic acid.

[0067] Examples of compounds having a hydroxyl group include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, glycerin, sorbitol, glucose, and sucrose.

[0068] Examples of the amide compound include N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N,N-diethylacetamide, N-methylpyrrolidinone, γ-butyrolactam, and ε-caprolactam.

[0069] Examples of compounds having an ether structure include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol butyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol diacetate, diethylene glycol dibenzoate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, diethylene glycol bis(p-toluenesulfonic acid), diethylene glycol bis(3-aminopropyl)ether, 1,2-bis(2-aminoethoxy)ethane, dipropylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol diethyl ether.

[0070] To perform interfacial polycondensation on the porous support layer, the surface of the porous support layer is first coated with an aqueous polyfunctional aromatic amine solution. The concentration of the polyfunctional aromatic amine in the aqueous polyfunctional aromatic amine solution is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 15% by mass or less. Furthermore, the concentration of compound X is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less, from the viewpoint of sufficiently achieving intermediate layer formation and suppressing disturbance of the intermediate layer to stably form a separation functional layer.

[0071] The method for coating the surface of the porous support layer with an aqueous polyfunctional aromatic amine solution may be any method that uniformly and continuously coats the surface of the porous support layer with the aqueous solution, and includes known coating methods such as coating the surface of the porous support layer with the aqueous solution or immersing the porous support layer in the aqueous solution. The contact time between the porous support layer and the aqueous polyfunctional aromatic amine solution is preferably 5 seconds to 10 minutes, more preferably 10 seconds to 3 minutes. Next, it is preferable to remove the excess aqueous solution by a draining process. Examples of draining methods include holding the membrane surface vertically and allowing it to flow naturally. After draining, the membrane surface may be dried to remove all or part of the water in the aqueous solution.

[0072] Thereafter, the above-mentioned polyfunctional aromatic acid chloride solution is applied to the porous support layer coated with the polyfunctional aromatic amine aqueous solution, and a crosslinked aromatic polyamide is formed by interfacial polycondensation.

[0073] In the method for producing a composite semipermeable membrane of this embodiment, the water content in the organic solvent in which the polyfunctional acid halide is dissolved is preferably 50 ppm or less. By reducing the water content in the organic solvent, inhibition of the polycondensation reaction between the polyfunctional amine and the polyfunctional acid halide due to water can be suppressed, and an appropriate surface pore size can be formed. For the above reasons, the water content in the organic solvent in which the halide is dissolved is more preferably 30 ppm or less. Furthermore, by setting the water content in the organic solvent in which the polyfunctional acid halide is dissolved to 50 ppm or less, inhibition of the polymerization reaction can be suppressed, and the density of the surface layer of the separation functional layer can be maintained at a high level. This makes it easier to produce a separation functional layer in which the amide group density Nb near the surface layer of the separation functional layer is low and the amide group density Nd on the inner layer side is high.

[0074] The water content in an organic solvent can be measured by the Karl Fischer titration method described in JIS K0068: 2001. The Karl Fischer method includes volumetric titration and coulometric titration, but coulometric titration is suitable for analyzing trace amounts of water in organic solvents.

[0075] The method for producing the composite semipermeable membrane of the present embodiment is to dissolve a polyfunctional amine solution and a polyamine solution in a solution containing 200 mL / m of the surface area of ​​the porous support layer on the porous support layer. ２ More than 400mL / m ２ It is preferable to contact the porous support layer with the polyfunctional acid chloride solution in the amount of 200 mL / m2 or less to form a crosslinked polyamide layer by interfacial polycondensation. ２ More than 400mL / m ２ By setting the ratio within the following range, the intermediate layer will have an appropriate ratio, the interfacial polymerization reaction will proceed appropriately, and a separation functional layer having the desired amide group density or thickness can be produced.

[0076] The time for carrying out the interfacial polycondensation is preferably from 0.1 seconds to 3 minutes, more preferably from 0.1 seconds to 1 minute.

[0077] The concentration of the polyfunctional aromatic acid chloride in the polyfunctional aromatic acid chloride-containing solution is not particularly limited, but is preferably 0.01% by mass or more and 1.0% by mass or less from the viewpoint of sufficient formation of the separation functional layer and from the viewpoint of cost. Furthermore, the concentration of compound Y is preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.02% by mass or more and 0.5% by mass or less, from the viewpoint of sufficient formation of the intermediate layer and suppressing disturbance of the intermediate layer to stably form the separation functional layer.

[0078] Next, the organic solvent remaining after the reaction is preferably removed by a draining step. For example, the organic solvent can be removed by a method in which the membrane is held vertically and the excess organic solvent is allowed to flow down naturally. In this case, the vertical holding time is preferably 1 minute or more and 5 minutes or less, more preferably 1 minute or more and 3 minutes or less. Holding the membrane for 1 minute or more makes it easier to obtain a crosslinked aromatic polyamide having the desired functionality, while holding the membrane for 5 minutes or less can prevent defects due to excessive drying of the organic solvent, thereby preventing performance degradation.

[0079] (3) Use of Composite Semipermeable Membrane The composite semipermeable membrane of this embodiment is wound around a cylindrical water collection pipe having many holes, together with a raw water flow path material such as a plastic net, a permeate water flow path material such as tricot, and, if necessary, a film for increasing pressure resistance, and is suitably used as a spiral composite semipermeable membrane element. Furthermore, this element can be connected in series or in parallel and housed in a pressure vessel to form a composite semipermeable membrane module.

[0080] Furthermore, the composite semipermeable membranes, their elements, and modules can be combined with a pump that supplies raw water to them, a device that pretreats the raw water, etc. to form 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 did not permeate the membrane, thereby obtaining water suitable for the intended purpose.

[0081] The temperature of the feed water to the fluid separation device is preferably 5° C. or higher and 45° C. or lower from the viewpoint of improving the salt rejection rate and the membrane permeation flux. In addition, in order to suppress the generation of scale such as magnesium and to suppress membrane deterioration, it is preferable to operate the device with the pH of the feed water in the neutral range.

[0082] The module using the composite semipermeable membrane of this embodiment is characterized by its high separation ability for nonionic solutes, and can be particularly suitably introduced into processes, such as those for producing ultrapure water from raw water containing trace amounts of organic matter and silicates, such as those used in the production of ultrapure water in semiconductor manufacturing.

[0083] (3-1) Ultrapure Water Production Method The method for producing ultrapure water described below includes, as shown in Figure 5, a pretreatment step for removing suspended solids from raw water, a primary treatment step (reverse osmosis step) that uses a reverse osmosis membrane to remove silica from the aqueous solution after the pretreatment step, and a secondary treatment step for removing ionic components from the aqueous solution that has been subjected to the step using the reverse osmosis membrane. Note that in the ultrapure water production method according to this embodiment, only the reverse osmosis step is essential, and the other steps are optional. Each of the above steps will be described below.

[0084] (3-2) Pretreatment Step (3-2-1) Raw Water The target supply water (raw water) in this embodiment is an aqueous solution containing silica (silica-containing aqueous solution), and specific examples include river water, groundwater, recycled wastewater, and cooling water blowdown. Silica often exists as silicate, and its charge state changes depending on the pH of the raw water, but it is unlikely to be charged in the neutral range (pH 6 to 8). Boric acid also changes its charge state depending on the pH of the raw water, but it is unlikely to be charged in the neutral range (pH 6 to 8).

[0085] (3-2-2) Pretreatment Method The method for producing ultrapure water according to this embodiment preferably includes a pretreatment step for removing suspended solids from the silica-containing aqueous solution prior to the primary treatment step (reverse osmosis step) described below. If suspended solids contained in the raw water adhere to the surface of the reverse osmosis membrane in the subsequent primary treatment step, they can cause clogging (fouling). Therefore, fouling can be suppressed by passing part or all of the raw water through an MF membrane (microfiltration membrane) or a UF membrane (ultrafiltration membrane) for filtration (pretreatment) before supplying it to the primary treatment step.

[0086] (3-3) Primary Treatment Step (Reverse Osmosis Step) (3-3-1) Reverse Osmosis Membrane (RO Membrane) The method for producing ultrapure water of this embodiment includes a reverse osmosis step in which silica is removed from a silica-containing aqueous solution using the composite semipermeable membrane of this embodiment. That is, the method for producing ultrapure water of this embodiment includes a step in which raw water or an aqueous solution treated in a pretreatment step is treated with the composite semipermeable membrane of this embodiment as a reverse osmosis membrane in the primary treatment step to separate and remove silica.

[0087] The composite semipermeable membrane of this embodiment used as a reverse osmosis membrane preferably has removal and water permeability properties that satisfy the following formulas (1) to (3) when water containing 500 ppm of NaCl, 20 ppm of silica, and 1 ppm of boron is passed through it at an operating pressure of 0.75 MPa: Silica removal rate ≧ 99.30% (formula (1)), Boron removal rate ≧ 60% (formula (2)), and Permeate volume ≧ 0.85 m ３ / m ２ / day...Formula (3)

[0088] Surprisingly, it was found that the composite semipermeable membrane of this embodiment exhibits high selectivity and is resistant to a decrease in silica removal rate even when exposed to oxidizing agents such as hypochlorous acid solution, which are used as chemicals for cleaning UF membranes and piping in pretreatment processes. While the details of the reason for this are unclear, sodium hypochlorite expands the size of the fine pores in the reverse osmosis membrane's pore structure that contribute to boric acid removal, increasing water permeability. Meanwhile, by maintaining a pore size that is smaller than silica, which is larger than boric acid, the ratio of water to silica permeability is maintained, which is thought to suppress a decrease in silica removal rate and reduce the silica concentration in the permeate. Furthermore, the high water permeation rate allows for a reduction in the amount of concentrated water (waste water) during high-recovery operation without increasing operating pressure, thereby achieving a highly efficient process.

[0089] Furthermore, by using the composite semipermeable membrane of the present embodiment that satisfies the following formulas (4) and (5), the load on the subsequent secondary treatment step can be reduced, a highly efficient process can be realized, and the generation of silica scale on the membrane surface can be suppressed, which is preferable: 99.90% > NaCl removal rate ≥ 99.50% (formula (4)) (NaCl removal rate) - (silica removal rate) ≤ 0.20% (formula (5))

[0090] Although the details of this action are unknown, the following mechanism is thought to be the case. When an aqueous solution containing silica and other ions is filtered, the components removed at the reverse osmosis membrane surface are concentrated on the membrane surface, resulting in a high concentration. Silica typically has a solubility of 120 mg / L in water at 25°C. If this solubility is exceeded, it precipitates as scale, covering the surface of the reverse osmosis membrane and causing filtration resistance, resulting in a decrease in permeability. On the other hand, the solubility of this silica decreases as the surrounding ion concentration increases. Therefore, when the sodium chloride removal rate is high, the total concentration of ions such as sodium chloride concentrated on the membrane surface increases locally, and similarly, silica concentrated on the membrane surface exceeds its solubility and precipitates, forming scale that covers the surface of the reverse osmosis membrane, resulting in a decrease in permeability.

[0091] Furthermore, when the value obtained by subtracting the silica removal rate from the NaCl removal rate is greater than 0.20%, although not all the details are clear, there is a large degree of unevenness in the membrane structure that affects the removability, resulting in a mixture of areas with high and low removability, and the sodium chloride concentration on the membrane surface becomes high in the areas with high removability, which reduces the solubility of silica and leads to the formation of silica scale, which causes filtration resistance and is likely to lead to a decrease in water permeability.

[0092] (3-3-2) Operation Method In filtration using a reverse osmosis membrane, it is preferable to supply raw water or a pretreated aqueous solution to the reverse osmosis membrane at a pressure in the range of 0.10 MPa or more and 12 MPa or less. If the pressure is 0.10 MPa or more, a decrease in the membrane permeation rate of water can be suppressed, and if it is 12 MPa or less, the possibility of affecting membrane damage can be reduced. Furthermore, if the pressure is supplied at 0.25 MPa or more and 6 MPa or less, the membrane permeation flux is high, allowing the aqueous solution to permeate efficiently and reducing the possibility of affecting membrane damage, which is more preferable, and supplying at 0.25 MPa or more and 1 MPa or less is particularly preferable. If the amount of water permeated through the reverse osmosis membrane is 0.85 m ３ / m ２ / day or more, a sufficient amount of permeate can be obtained even under low-pressure operation of 1 MPa or less, which reduces the energy consumption per unit of water produced and the cost of producing fresh water. In addition, it becomes possible to design the equipment using a small-scale pump, which allows for space savings.

[0093] The primary treatment step may be a multi-stage treatment, i.e., the pretreated aqueous solution may be filtered through a first reverse osmosis membrane and the resulting permeate may be treated again through a second reverse osmosis membrane. Alternatively, to reduce waste water and increase recovery, the concentrate obtained by filtration through the first reverse osmosis membrane may be treated through a second reverse osmosis membrane.

[0094] (3-4) Secondary Treatment Step The method for producing ultrapure water according to this embodiment preferably further comprises a step of removing solute salts from the aqueous solution treated in the reverse osmosis step using an ion exchange resin. That is, it preferably comprises a secondary treatment step of further removing ionic components from the aqueous solution, which is the permeate obtained in the primary treatment step, to produce ultrapure water. The secondary treatment step preferably uses an ion exchange resin (ion exchanger).

[0095] Methods using ion exchange resins include the use of an ion exchange device containing a cation exchange resin and an anion exchange resin, or the use of electrical deionization (EDI). An EDI is a device that has a deionization compartment separated by an ion exchange membrane and filled with an ion exchanger, a concentration compartment that concentrates the ions desalted in the desalting compartment, and an anode and a cathode for passing an electric current. By passing an electric current through the device, the device simultaneously deionizes (demines) the water to be treated using the ion exchanger and regenerates the ion exchanger. The water to be treated that is passed through the EDI is desalinated by the ion exchanger filled in the desalting compartment and is discharged outside the EDI as EDI-treated water. Similarly, concentrated water with concentrated ions is discharged outside as EDI-concentrated water.

[0096] Furthermore, the secondary treatment step may include UV treatment. If the silica concentration in the aqueous solution supplied from the primary treatment step is high, silica will precipitate on the surface of the ion exchange resin in the secondary treatment step, causing a decrease in the treatment efficiency or deterioration of the secondary treatment step.

[0097] The present invention will be described below with reference to examples, but the present invention is not limited to these examples in any way.

[0098] [1. Measurement of Properties] (Water content of organic solvent in interfacial polycondensation) Measurement was carried out by Karl Fischer coulometric titration using a trace water content measuring device (CA-200 manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0099] (NaCl Rejection Rate, Silica Rejection Rate, Boron Rejection Rate) Feed water adjusted to a temperature of 25°C, pH 7, sodium chloride 500 ppm, sodium metasilicate 87 ppm (20 ppm as silica), and boric acid 5.7 ppm (1 ppm as boron) was supplied to a composite semipermeable membrane at an operating pressure of 0.75 MPa, and membrane filtration was performed. The electrical conductivity of the feed water and permeate was measured using an electrical conductivity meter (CM-41X, manufactured by Toa Denpa Kogyo Co., Ltd.) to obtain the practical salinity, i.e., NaCl concentration, of each. The NaCl rejection rate was calculated from the obtained NaCl concentrations according to the following formula. Here, NaCl concentration (ppm) means the concentration on a mass basis. NaCl rejection rate (%) = 100 × {1 - (NaCl concentration in permeate water / NaCl concentration in feed water)}. The silica and boron concentrations in the feed water and permeate water were measured using an ICP emission spectrometer (5110VDV manufactured by Agilent), and the silica removal rate and boron removal rate were calculated using the following formulas: Silica removal rate (%) = 100 × {1 - (silica concentration in permeate water / silica concentration in feed water)} Boron removal rate (%) = 100 × {1 - (boron concentration in permeate water / boron concentration in feed water)}

[0100] (Permeated Water Amount) In the test in the preceding paragraph, the amount of water permeated through the membrane was measured, and the value converted into the amount of water permeated (cubic meters) per square meter of membrane surface per day was defined as the permeated water amount (m ３ / m ２ / day).

[0101] (Preparation of Amino Group Density Measurement Sample) A 5 cm square composite semipermeable membrane from which the substrate was physically peeled was treated by the cryo-ultrathin sectioning method, placed on a grid, immersed in pure water for 4 hours, and then immersed in a 10% by mass aqueous solution of 2-propanol for 1 hour for washing. Thereafter, the membrane was washed with NaCl solution adjusted to pH 3.8 and 25°C. ２ WO ４ ・2H ２ 1.0 x 10 －３ The sample was immersed in a 2000 mol / L aqueous solution for 10 minutes three times, followed by a 2000 mol / L aqueous solution of Na ２ WO ４ ・2H ２ 1.0 x 10 －７The sample was immersed in the 200 mol / L aqueous solution for 7 minutes, and this process was repeated four times. After that, the water content of the sample was removed with filter paper and then freeze-dried to obtain a sample for amino group density measurement.

[0102] (Amino group density) The composite semipermeable membrane sample prepared in the previous section was photographed using a field emission transmission electron microscope (HF5000 manufactured by Hitachi High-Technologies) under the condition of an acceleration voltage of 200 kV, and an STEM image was obtained at a magnification of 100,000. The obtained image was then analyzed using image processing software, and the amino group density for each of the regions a to e was calculated from the brightness value by the method described in "(ii) Amino group density" above.

[0103] (Amount of terminal amino group A, amount of terminal carboxy group B, amount of amide group C) Composite semipermeable membrane 5m ２ The substrate was physically peeled off from the substrate, and the porous support layer and separation function layer were recovered. After drying by leaving it to stand at 25 ° C for 24 hours, it was added little by little to a beaker containing dichloromethane and stirred to dissolve the polymer that constitutes the porous support layer, and the insoluble matter in the beaker was recovered with filter paper. This insoluble matter was placed in a beaker containing dichloromethane and stirred, and the insoluble matter in the beaker was recovered. This process was repeated until elution of the polymer that forms the porous support layer could no longer be detected in the dichloromethane solution. The recovered separation function layer was dried in a vacuum dryer to remove any remaining dichloromethane. The obtained separation function layer was freeze-pulverized to form a powder sample, which was sealed in a sample tube used for solid-state NMR measurement and analyzed by CP / MAS and DD / MAS. １３ C solid state NMR measurement was carried out. １３ For the C solid-state NMR measurement, a CMX-300 manufactured by Chemagnetics was used. The measurement conditions are as follows: Reference substance: polydimethylsiloxane (internal standard: 1.56 ppm) Sample rotation speed: 10.5 kHz Pulse repetition time: 100 s From the obtained spectrum, peak division was performed for each peak derived from the carbon atom to which each functional group was bonded, and the functional group amount ratio was quantified from the area of ​​the divided peaks.

[0104] (NaCl Removal Rate after Contact with Aqueous Sodium Hypochlorite Solution) A reverse osmosis membrane (10 cm x 10 cm) was immersed in 5 L of an aqueous solution containing 10 mg / L of sodium hypochlorite and adjusted to a pH of 7, and maintained at 25°C for 96 hours. Thereafter, the NaCl removal rate was measured using the method described in the above-mentioned "NaCl Removal Rate, Silica Removal Rate, and Boron Removal Rate." When the NaCl removal rate after contact with an aqueous sodium hypochlorite solution was 98.90% or higher, it was determined that the membrane had good resistance to performance degradation due to contact with sodium hypochlorite.

[0105] (Amount of silica scale deposition) Feed water was subjected to membrane filtration treatment by the method described in the above "NaCl removal rate, silica removal rate, and boron removal rate" and the total permeate volume was 100 L / m ２ For the composite semipermeable membranes that reached this point, deposits on the membrane surface were extracted with a 1% by mass aqueous solution of nitric acid, and the total adsorption amount (mg) of silica components was measured using an ICP emission spectrometer (5110VDV manufactured by Agilent). The amount of silica scale adhesion (mg / m) was calculated from the membrane area of ​​the separation membrane element. ２ The amount of silica scale adhesion was calculated as 0.2 mg / m ２ When the thickness was less than 100 μm, it was judged that the resistance to silica scale formation was good.

[0106] [2. Preparation of composite semipermeable membrane] (Comparative Example 1) A polyester nonwoven fabric (air permeability 2.0 cc / cm) made of long fibers was used. ２ A 15.0 mass % DMF solution of polysulfone was cast onto the support membrane (a 1000-membrane porous support layer) at 25°C, and the support membrane was immediately immersed in pure water and left for 5 minutes to produce a support membrane with a porous support layer thickness of 40 μm. Next, the support membrane was immersed in a 2.0 mass % m-PDA aqueous solution, after which excess aqueous solution was removed. Further, a solution prepared using n-decane with a water content of 40 ppm to give a TMC concentration of 0.10 mass % was added at 300 mL / m so that the surface of the porous support layer was completely wetted. ２ Next, in order to remove excess solution from the membrane, the membrane was placed vertically to drain the liquid, and then dried by blowing air at 25°C onto it using a fan, followed by washing with pure water at 80°C to obtain a composite semipermeable membrane of Comparative Example 1.

[0107] (Comparative Example 2) Polyester nonwoven fabric made of long fibers (breathability 2.0 cc / cm ２ A 15.0 mass% DMF solution of polysulfone was cast onto the support membrane (m-PDA) at 25°C, and immediately immersed in pure water and left for 5 minutes to produce a support membrane with a porous support layer thickness of 40 μm. Next, this support membrane was immersed in a 1.5 mass% aqueous solution of 2.0 mass% m-PDA and dipropylene glycol (hereinafter referred to as "DPG"; octanol / water partition coefficient -1.50) as compound X, after which excess aqueous solution was removed. Further, a solution prepared using n-decane with a water content of 40 ppm, a TMC concentration of 0.10 mass%, and a N,N-dimethylacetamide (hereinafter referred to as "DMAc"; octanol / water partition coefficient -0.77) concentration of compound Y, was added at 300 mL / m so that the surface of the porous support layer was completely wetted. ２ Next, in order to remove excess solution from the membrane, the membrane was placed vertically to drain the liquid, and then dried by blowing air at 25°C onto it using a fan, followed by washing with pure water at 80°C to obtain a composite semipermeable membrane of Comparative Example 2.

[0108] Comparative Example 3 A composite semipermeable membrane of Comparative Example 3 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.0 mass% ethylene glycol dimethyl ether (hereinafter referred to as "EGDME": octanol / water partition coefficient -0.21) and compound Y was changed to 0.1 mass% diethylene glycol methyl ethyl ether (hereinafter referred to as "DEGMEE": octanol / water partition coefficient -0.10).

[0109] Comparative Example 4 A composite semipermeable membrane of Comparative Example 4 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.5% by mass of DMAc and compound Y was changed to 0.1% by mass of EGDME.

[0110] Comparative Example 5 A composite semipermeable membrane of Comparative Example 5 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.0 mass% EGDME and compound Y was changed to 0.1 mass% diethylene glycol dimethyl ether (hereinafter referred to as "DEGDME": octanol / water partition coefficient -0.36).

[0111] Comparative Example 6 A composite semipermeable membrane of Comparative Example 6 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.2 mass% DEGMEE and compound Y was changed to 0.1 mass% diethylene glycol ethyl ether acetate (hereinafter referred to as "DEGEEAc"; octanol / water partition coefficient: 0.24).

[0112] (Comparative Example 7) Polyester nonwoven fabric made of long fibers (breathability 2.0 cc / cm ２ A 15.0 mass% DMF solution of polysulfone was cast onto the support membrane at 25°C under the condition of 25°C, and immediately immersed in pure water and left for 5 minutes to produce a support membrane with a porous support layer thickness of 40 μm. Next, this support membrane was immersed in an aqueous solution of 2.0 mass% m-PDA and 1.5 mass% DPG as Compound X, after which excess aqueous solution was removed. Further, a solution prepared using n-decane with a water content of 40 ppm so as to have a TMC concentration of 0.10 mass% was added at 300 mL / m so as to completely wet the surface of the porous support layer. ２ Next, in order to remove excess solution from the membrane, the membrane was placed vertically to drain the liquid, and then dried by blowing air at 25°C onto it using a fan, followed by washing with pure water at 80°C to obtain a composite semipermeable membrane of Comparative Example 7.

[0113] (Comparative Example 8) Polyester nonwoven fabric made of long fibers (breathability 2.0 cc / cm ２ A 15.0 mass % DMF solution of polysulfone was cast onto the support membrane (a 40 μm thick support membrane) at 25°C, and the support membrane was immediately immersed in pure water and left for 5 minutes to produce a support membrane with a porous support layer thickness of 40 μm. Next, the support membrane was immersed in a 2.0 mass % m-PDA aqueous solution, after which excess aqueous solution was removed. Further, a solution prepared using n-decane with a water content of 40 ppm, with a TMC concentration of 0.10 mass % and a DMAc concentration as compound Y of 0.1 mass %, was added at 300 mL / m so that the surface of the porous support layer was completely wetted. ２ Next, in order to remove excess solution from the membrane, the membrane was placed vertically to drain the liquid, and then dried by blowing air at 25°C onto it using a fan, followed by washing with pure water at 80°C to obtain a composite semipermeable membrane of Comparative Example 8.

[0114] Comparative Example 9 A composite semipermeable membrane of Comparative Example 9 was obtained in the same manner as in Comparative Example 8, except that compound Y was changed to 0.1% by mass of DEGEEAc.

[0115] Example 1 A composite semipermeable membrane of Example 1 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.2 mass % of DEGMEE and compound Y was changed to 0.1 mass % of DEGDME.

[0116] Example 2 A composite semipermeable membrane of Example 2 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.0 mass% EGDME and compound Y was changed to 0.03 mass% γ-butyrolactam (octanol / water partition coefficient: −0.71).

[0117] Example 3 A composite semipermeable membrane of Example 3 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.4 mass% of ε-caprolactam (octanol / water partition coefficient: −0.19) and compound Y was changed to 0.02 mass% of N-methylformamide (hereinafter referred to as “NMF”: octanol / water partition coefficient: −0.97).

[0118] Example 4 A composite semipermeable membrane of Example 4 was obtained in the same manner as in Comparative Example 2, except that compound X was changed to 1.2 mass% DEGMEE and compound Y was changed to 0.1 mass% diethylene glycol diacetate (hereinafter referred to as "DEGAc"; octanol / water partition coefficient -0.49).

[0119] Example 5 A composite semipermeable membrane of Example 5 was obtained in the same manner as in Example 4, except that an n-decane solution with a water content of 20 ppm was used.

[0120] (Example 6) The amount of n-decane solution applied was 180 mL / m ２ A composite semipermeable membrane of Example 6 was obtained in the same manner as in Example 4, except that the above-mentioned

[0121] (Example 7) The amount of n-decane solution applied was 420 mL / m ２ A composite semipermeable membrane of Example 7 was obtained in the same manner as in Example 4, except that the above-mentioned

[0122] Example 8 A composite semipermeable membrane of Example 8 was obtained in the same manner as in Example 7, except that an n-decane solution with a water content of 70 ppm was used.

[0123] The structures of the composite semipermeable membranes obtained in Comparative Examples 1 to 9 and Examples 1 to 8 are shown in Table 1, and their performances are shown in Table 2.

[0124]

[0125]

[0126] Thus, the membranes of Examples 1 to 8, in which the Nb / Nd ratio was 0.40 or less, achieved both high water permeability and high removal efficiency. －２４ mol / nm ２ or less, and Nd is 2.5 × 10 －２４ mol / nm ２ Membranes that satisfy the above criteria have been found to exhibit particularly high performance.

[0127] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2022-090653) filed on June 3, 2022, the contents of which are incorporated herein by reference.

[0128] 1 Composite semipermeable membrane 2 Substrate 3 Porous support layer 4 Separation function layer 11 First surface of composite semipermeable membrane 12 Second surface of composite semipermeable membrane 21 Convex portion i 22 Convex portion ii 23 Height of convex portion i 24 Height of convex portion ii 25 Inner surface of thin film 26 Outer surface of thin film 27 Thickness of thin film X Mean line of roughness curve Yp1-5 Elevation of the highest peak to the fifth peak from X Yv1-5 Elevation of the lowest valley bottom to the fifth valley bottom from X L Reference length P Reference point V0 Normal line passing through reference point P V1, V2 Straight lines parallel to normal line V0 Z1 Tangent to the outer surface of the thin film passing through reference point P Z2 Tangent to the inner surface of the thin film parallel to tangent line Z1

Claims

1. A composite semipermeable membrane comprising a porous support layer and a separation functional layer located on the porous support layer, wherein the composite semipermeable membrane has a first surface that faces the separation functional layer and a second surface that is the surface opposite to the first surface, the separation functional layer contains crosslinked polyamide, and the amino group density measured by scanning transmission electron microscopy (STEM) in a cross section in the thickness direction of the separation functional layer satisfies Nb / Nd≦0.40, where Nb: amino group density of region b, Nd: amino group density of region d, and Regions a-e: regions obtained by dividing the cross section into five equal parts in the thickness direction of the separation functional layer, and Regions a-e are aligned from the first surface toward the second surface.

2. The Nb is 1.0 × 10 －２４ mol / nm ２ or less, and the Nd is 2.5 × 10 －２４ mol / nm ２ The composite semipermeable membrane according to claim 1 .

3. The composite semipermeable membrane according to claim 1 or 2, wherein, when the amount of terminal amino groups in the crosslinked polyamide is A, the amount of terminal carboxyl groups is B, and the amount of amide groups is C, C / (A+B) is 1.7 or more.

4. The composite semipermeable membrane according to claim 1 or 2, wherein the separating functional layer has a thin film whose main component is crosslinked polyamide, and the thickness of the thin film is 9.0 nm or more and 13.0 nm or less.

5. The composite semipermeable membrane according to claim 1 or 2, which satisfies the following formulas (1) to (5) when water containing 500 ppm of sodium chloride, 20 ppm of silica, and 1 ppm of boron is passed through the composite semipermeable membrane at an operating pressure of 0.75 MPa: silica removal rate ≧ 99.30% (formula (1)); boron removal rate ≧ 60% (formula (2)); and permeate volume ≧ 0.85 m. ３ / m ２ / day Equation (3) 99.90% > NaCl removal rate ≧ 99.50% Equation (4) (NaCl removal rate) - (silica removal rate) ≦ 0.20% Equation (5) 6. A method for producing a composite semipermeable membrane, which comprises contacting a polyfunctional amine solution containing compound X with a polyfunctional acid halide solution containing compound Y on a porous support layer to form a polyamide layer by an interfacial polycondensation reaction, wherein the octanol / water partition coefficients of compound X and compound Y satisfy the following formulas (6) to (8): Log P(X) < 0 (6) Log P(Y) < 0 (7) Log P(X) / Log P(Y) < 0.50 (8) 7. The method for producing a composite semipermeable membrane according to claim 6, wherein the water content of the organic solvent in which the polyfunctional acid halide is dissolved is 50 ppm or less.

8. On the porous support layer, the polyfunctional amine solution and the surface area of ​​the porous support layer are mixed at a rate of 200 mL / m ２ More than 400mL / m ２ The method for producing a composite semipermeable membrane according to claim 6 or 7, wherein the polyamide layer is formed by an interfacial polycondensation reaction by contacting the polyfunctional acid halide solution with the polyfunctional acid halide solution in an amount of:

9. A method for producing ultrapure water, comprising a reverse osmosis step of removing silica from a silica-containing aqueous solution using the composite semipermeable membrane of claim 1 or 2.

10. The method for producing ultrapure water according to claim 9, further comprising a pretreatment step of removing suspended solids from the silica-containing aqueous solution prior to the reverse osmosis step.

11. The method for producing ultrapure water according to claim 10, further comprising the step of removing solute salts from the aqueous solution treated in the reverse osmosis step using an ion exchange resin.

12. A composite semipermeable membrane element comprising the composite semipermeable membrane according to claim 1 or 2.

13. A composite semipermeable membrane module comprising the composite semipermeable membrane element according to claim 12.