Composite semipermeable membrane and method for producing same

Abstract

Provided is a composite semipermeable membrane having a porous support layer and a separation function layer positioned on the porous support layer, wherein: the surfaces of the composite semipermeable membrane include a first surface that is a surface in a direction on the side of the porous support layer where the separation function layer is present, and a second surface that is the surface on the opposite side from the first surface; the separation function layer contains a crosslinked polyamide; and A / B is 1.40 or less, where A is the proportion of coarse holes having a hole diameter of 0.7 nm or greater in a region a, and B is the proportion of coarse holes having a hole diameter of 0.7 nm or greater in a region b, when a thickness-direction cross-section of the separation function layer observed using a scanning electron microscope is equally divided into the region a, which is on the first-surface side, and the region b, which is on the second-surface side.

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 and a method for producing the same. The present invention also relates to a composite semipermeable membrane element comprising the composite semipermeable membrane, and a composite semipermeable membrane module comprising the composite semipermeable membrane element. The present invention also relates to a method for producing ultrapure water using the composite semipermeable membrane.

[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] Examples of membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, etc. These membranes are used, for example, for producing drinking water or industrial ultrapure water from seawater, brackish water, water containing harmful substances, etc., for wastewater treatment, and for recovering valuable resources.

[0004] Many of the currently commercially available reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes. Among them, a composite semipermeable membrane (Patent Document 1) obtained by coating a microporous support membrane with a separation functional layer made of a crosslinked aromatic polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide is widely used as a separation membrane with high water generation ability and high selective separation ability for salts and neutral molecules.

[0005] International Publication No. 2010 / 096563

[0006] However, when using conventional composite semipermeable membranes to remove neutral molecules contained in raw water, their water production and selective separation properties were insufficient, posing a problem in terms of membrane performance.

[0007] Therefore, an object of the present invention is to provide a composite semipermeable membrane that is excellent in permeation rate and neutral molecule removal.

[0008] In order to solve the above problems, the present invention includes the following configurations [1] to

[14] . [1] A composite semipermeable membrane having a porous support layer and a separation functional layer located on the porous support layer, wherein the surface of the composite semipermeable membrane has a first side which is the side of the porous support layer on which the separation functional layer is located, and a second side which is the side opposite to the first side, and the separation functional layer contains a cross-linked polyamide, wherein a cross section of the separation functional layer in the thickness direction observed with a scanning transmission electron microscope is equally divided into a region a on the first side and a region b on the second side, and when A is the proportion of coarse pores with a pore diameter of 0.7 nm or more in region a and B is the proportion of coarse pores with a pore diameter of 0.7 nm or more in region b, A / B is 1.40 or less. [2] The composite semipermeable membrane according to [1] above, wherein the proportion A of coarse pores is 0.10 or less. [3] A composite semipermeable membrane having a porous support layer and a separation functional layer located on the porous support layer, wherein the surface of the composite semipermeable membrane has a first surface that is the surface on the side of the porous support layer where the separation functional layer is present, and a second surface that is the surface opposite to the first surface, wherein the separation functional layer contains a crosslinked polyamide, and wherein the carboxy group density ratio Nd / Nf measured by a scanning transmission electron microscope in a cross section in the thickness direction of the separation functional layer is 2.1 or less. Nd: carboxy group density of region d Nf: carboxy group density of region f Regions d and f: regions included in regions c to g obtained by dividing the cross section in the thickness direction of the separation functional layer into five equal parts in the thickness direction of the separation functional layer, and regions c to g are aligned from the first surface toward the second surface. [4] Nd is 2.3 × 10 －２６ mol / nm ２ or less, and the Nf is 0.7 × 10 －２６ mol / nm ２[5] The composite semipermeable membrane according to any one of [1] to [4] above, wherein, when the amount of terminal amino groups in the crosslinked polyamide is C, the amount of terminal carboxy groups is D, and the amount of amide groups is E, the ratio E / (C+D) is 1.7 or more. [6] The composite semipermeable membrane according to any one of [1] to [5] above, wherein the static contact angle of water on the surface of the separation functional layer is 40 degrees or more and 120 degrees or less. [7] A composite semipermeable membrane element comprising the composite semipermeable membrane according to any one of [1] to [6] above. [8] A composite semipermeable membrane module comprising the composite semipermeable membrane element according to [7] above. [9] A method for producing a composite semipermeable membrane comprising a support membrane having a substrate and a porous support layer, and a separation functional layer provided on the porous support layer, wherein the separation functional layer is formed by interfacial polycondensation of a polyfunctional amine aqueous solution and a polyfunctional acid halide solution on the porous support layer, wherein the polyfunctional amine aqueous solution contains a polyfunctional amine, a monofunctional amine having a molecular weight of 150 or less, and an aqueous phase additive having an amide group or a urea group, and the polyfunctional acid halide solution contains a polyfunctional acid halide and an organic solvent.

[10] A method for producing the composite semipermeable membrane according to [9] above, wherein the monofunctional amine has a molecular weight of 100 or less.

[11] A method for producing the composite semipermeable membrane according to [9] or

[10] above, wherein the water content in the organic solvent is 10 ppm or more and 50 ppm or less.

[12] A method for producing a composite semipermeable membrane according to any one of [9] to

[11] above, wherein the concentration of the monofunctional amine in the aqueous polyfunctional amine solution is 0.01 mass% or more and 10 mass% or less.

[13] A method for producing a composite semipermeable membrane according to any one of [9] to

[12] above, wherein the concentration of the aqueous polyfunctional amine solution is 0.01 mass% or more and 10 mass% or less.

[14] 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 according to any one of [1] to [6] above.

[0009] According to the present invention, a composite semipermeable membrane can be obtained that achieves both a high permeation rate and the ability to remove middle molecules.

[0010] FIG. 1 is a schematic diagram showing a cross section of a composite semipermeable membrane according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing a cross section of a pleated structure in a separation functional layer. FIG. 3 is a schematic diagram explaining a method for measuring 10-point average surface roughness. FIG. 4 is a schematic diagram showing the state when water is dropped onto the surface of a separation functional layer. FIG. 5 is a schematic diagram showing regions a and b in a cross section in the thickness direction of the separation functional layer. FIG. 6 is a schematic diagram showing regions c, d, e, f, and g in a cross section in the thickness direction of the separation functional layer. FIG. 7 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 , the composite semipermeable membrane 1 according to this embodiment comprises a porous support layer 3 and a separation function layer 4 located on the porous support layer. Of the surfaces of the composite semipermeable membrane 1, the surface facing the porous support layer 3 toward the separation function layer 4 is referred to as a first surface 11, and the surface opposite to the first surface is referred to as a second surface 12.

[0013] The composite semipermeable membrane according to this embodiment includes a first embodiment that satisfies the following condition 1 and a second embodiment that satisfies the following condition 2. Condition 1: In the separation functional layer, the ratio of coarse pores, A / B, described below, is 1.40 or less. Condition 2: In the separation functional layer, the ratio of carboxy group density, Nd / Nf, described below, is 2.1 or less.

[0014] In any of the composite semipermeable membranes of the present embodiment, the polyamide structure near the surface layer of the separation functional layer has a structure that is denser than the polyamide structure of the inner layer to a certain degree, thereby achieving excellent permeation capacity and neutral molecule removal. Note that the composite semipermeable membrane of the present embodiment only needs to satisfy at least one of condition 1 and condition 2, and may also satisfy both. In addition, in this specification, the "composite semipermeable membrane of the present embodiment" includes both the first embodiment and the second embodiment, unless otherwise specified.

[0015] (1-1) Separation Functional Layer (1-1-1) Composition Among the components of the composite semipermeable membrane, the separation functional layer is the one that essentially 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.

[0016] The separation functional layer of the composite semipermeable membrane according to this embodiment contains a crosslinked polyamide. "Crosslinked polyamide" refers to a polycondensate of a polyfunctional amine and a polyfunctional acid halide. Because of its high chemical stability against acids and alkalis, the separation functional layer preferably contains a crosslinked polyamide as a main component. Here, "main component" refers to a component that accounts for 50% by mass or more of the components that make up the substance.

[0017] The crosslinked polyamide is preferably formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide, and at least one of the polyfunctional amine and the polyfunctional acid halide preferably contains a trifunctional or higher functional compound.

[0018] The term "polyfunctional amine" refers to an amine having at least two primary amino groups and / or secondary amino groups in one 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.

[0019] Among these, from the viewpoints of the removal performance, permeate amount, 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. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene. Among these, m-phenylenediamine (hereinafter referred to as "m-PDA") is more preferred from the viewpoints of ease of availability and ease of handling.

[0020] 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.

[0021] The term "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. Examples of 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.

[0022] From the viewpoint of reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride. Furthermore, from the viewpoint of the removal performance and heat resistance of the composite semipermeable membrane, the polyfunctional acid halide is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Among them, TMC is more preferred from the viewpoint of easy availability and ease of handling. These polyfunctional acid halides may be used alone or in combination of two or more.

[0023] The separation functional layer of the composite semipermeable membrane according to this embodiment preferably has a pleated structure. The "pleated structure" refers to a structure in which protruding convex portions as shown in FIG. 2 are repeatedly present. Here, the "convex portion" refers to the space between the apexes of adjacent portions (concave portions of the separation functional layer) that are convex toward the porous support layer in the pleated structure of the separation functional layer as shown in FIG. 2. One end of the convex portion (the apex of the concave portion) may be separated from the surface of the porous support layer and the other may be in contact with it, or both ends may be in contact with the porous support layer, or both ends may be separated from the surface of the porous support layer.

[0024] The thickness of the separation functional layer in the pleated structure (hereinafter also referred to as "pleat thickness") is preferably 8.0 nm or more and 20.0 nm or less, more preferably 9.0 nm or more and 13.0 nm or less, from the viewpoint of obtaining sufficient separation performance and permeate amount.

[0025] The pleat thickness 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 in the "Separation Functional Layer Formation Process" below.

[0026] The pleat thickness can be measured by photographing a cross section of the pleated structure using a transmission electron microscope (hereinafter referred to as "TEM") and then importing the cross-sectional photograph into image analysis software for analysis. Specifically, five convex portions are randomly selected from a TEM image of the cross section of the separation functional layer. For each convex portion (reference numerals 21 and 22 in FIG. 2 ), the pleat thickness (reference numeral 27 in FIG. 2 ) is measured at 10 points within a region extending from the apex of the convex portion to 90% of its height (reference numerals 23 and 24 in FIG. 2 , hereinafter also referred to as "convex portion height"), as shown in FIG. 2 . That is, as shown in FIG. 2 , the surface of the porous support layer is defined as 0% height, and the apex of the convex portion is defined as 100% height, and 10 measurement points are randomly selected within a range of 10 to 100% height. The arithmetic mean value calculated from the thicknesses at a total of 50 points is the "pleat thickness." Here, the convex portions to be measured when calculating the pleat thickness are those having a height equal to or greater than one-fifth of the 10-point average surface roughness.

[0027] The 10-point average surface roughness is calculated as follows. A cross section of the separation functional layer in the thickness direction is observed using an electron microscope. The observation magnification is preferably 10,000 to 100,000 times. In the obtained cross-sectional image, as shown in FIG. 3, the surface of the separation functional layer 4 appears as a pleated curve with continuously repeated convex and concave portions. A roughness curve defined in accordance with JIS B 0601:2013 (ISO 4287:1997) is obtained from this curve. A 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 portion, 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) is calculated, and this value, expressed in nanometers (nm), is the 10-point average surface roughness. 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 L is equal above and below the mean line.

[0028] In order to obtain a sufficient amount of water permeation, the median height of the convex portions of the separating functional layer in the composite semipermeable membrane according to this embodiment is preferably 80 nm or more and 300 nm or less, more preferably 120 nm or more and 300 nm or less, and even more preferably 160 nm or more and 300 nm or less.

[0029] The median value of the convex height is calculated as follows. When 10 cross sections of a composite semipermeable membrane are randomly observed, the height of all convex portions that are at least one-fifth of the above-mentioned 10-point average surface roughness is measured at each cross section. Furthermore, the median value can be calculated based on the calculation results for the 10 cross sections to determine the median value of the convex height. Here, each cross section has a width of 2.0 μm in the direction of the mean line of the roughness curve.

[0030] 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 during the process of forming the separation functional layer.

[0031] The static contact angle of water on the surface of the separating functional layer of the composite semipermeable membrane according to this embodiment is preferably 40 degrees or more and 120 degrees or less. Here, the "static contact angle of water" is a parameter that indicates the wettability and hydrophilicity of the separating functional layer surface, and a smaller contact angle means higher hydrophilicity. In the composite semipermeable membrane according to this embodiment, the reaction of the monofunctional amine near the surface of the separating functional layer reduces the proportion of coarse pores in the surface layer, or reduces the carboxy group density of the surface layer, thereby improving hydrophobicity. From the viewpoint of achieving both the amount of water permeated and the removability of the composite semipermeable membrane, the static contact angle is more preferably 60 degrees or more and 100 degrees or less.

[0032] As shown in Figure 4, when water is dropped onto the surface of the separation functional layer, the water becomes round due to surface tension, and the following equation (1), known as "Young's equation," holds true: γ Ｓ = γ Ｌ cosθ+γ ＳＬ ...Equation (1) where γ Ｓ is the surface tension of the separation functional layer, γ Ｌ is the surface tension of water, γ ＳＬ is the interfacial tension between the separation functional layer and water. The angle θ between the tangent to the water and the surface of the separation functional layer when the above formula (1) is satisfied is defined as the static contact angle of water. Note that since the static contact angle gradually decreases over time, the value 10 seconds after the water lands on the surface of the separation functional layer is defined as the static contact angle of water.

[0033] (1-1-2) Characteristics

[0034] (i) Proportion of Coarse Pores In the separating functional layer of the composite semipermeable membrane according to the first embodiment, a cross section (cross section perpendicular to the first surface) in the thickness direction observed with a scanning transmission electron microscope (hereinafter referred to as "STEM") is divided into two equal halves, a region a on the first surface side and a region b on the second surface side, and when the proportion of coarse pores with a pore diameter of 0.7 nm or more in region a is A and the proportion of coarse pores with a pore diameter of 0.7 nm or more in region b is B, A / B is 1.40 or less. Hereinafter, the proportion A of coarse pores with a pore diameter of 0.7 nm or more in region a and the proportion B of coarse pores with a pore diameter of 0.7 nm or more in region b will also be simply referred to as A and B, respectively.

[0035] A separation functional layer mainly composed of crosslinked polyamide formed by interfacial polycondensation has pores between polyamide chains and within the polyamide network structure that allow water molecules or solute molecules to pass through. If pores with a pore diameter of 0.7 nm or more are defined as coarse pores, a high proportion of coarse pores in a region means that the separation functional layer has a sparse structure. If the separation functional layer has a sparse structure, the water permeation resistance will be low, but the solute removal performance will also be low. On the other hand, a low proportion of coarse pores in a region means that the separation functional layer has a dense structure. If the separation functional layer has a dense structure, the water permeation resistance will be high, but the solute removal performance will be improved.

[0036] The present inventors have found that a separation functional layer having an A / B ratio of 1.40 or less can achieve both a particularly high permeate amount and neutral molecule removal ability. From the viewpoint of achieving both a high permeate amount and neutral molecule removal ability, A / B is preferably 0.10 or more and 1.40 or less, more preferably 0.80 or more and 1.35 or less, even more preferably 1.00 or more and 1.30 or less, and particularly preferably 1.10 or more and 1.30 or less.

[0037] As described below in the "Separation functional layer formation process," A / B can be controlled, for example, by the type and concentration of the aqueous layer additive having an amide group or urea group and the monofunctional amine contained in the polyfunctional amine aqueous solution, the ratio of the concentration of the monofunctional amine to the concentration of the polyfunctional amine, 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] In the composite semipermeable membrane according to this embodiment, the proportion A of coarse pores in region a is preferably 0.10 or less. A composite semipermeable membrane having a small proportion of coarse pores near the surface layer of the separation functional layer, i.e., a composite semipermeable membrane having a small value A, has a polyamide structure dense enough to be suitable for removing solutes, and the removal ability of the composite semipermeable membrane is improved. From the viewpoint of achieving both the removal performance and permeate amount of the composite semipermeable membrane, A is more preferably 0.01 or more and 0.10 or less, and even more preferably 0.03 or more and 0.08 or less.

[0039] In addition, a composite semipermeable membrane having a large proportion of coarse pores on the inner layer side of the separation functional layer, i.e., a composite semipermeable membrane having a large value of the proportion B of coarse pores in region b, has a polyamide structure that is coarse enough to reduce water permeation resistance, and improves the water permeation rate of the composite semipermeable membrane. On the other hand, from the viewpoint of maintaining the physical strength of the separation functional layer, B is preferably 0.01 or more and 0.20 or less, more preferably 0.03 or more and 0.18 or less, and even more preferably 0.05 or more and 0.15 or less.

[0040] As described below in the "Separation functional layer formation process," A and B can be controlled, for example, by the type and concentration of the aqueous layer additive having an amide group or urea group and the monofunctional amine contained in the polyfunctional amine aqueous solution, the water content contained in the organic solvent that dissolves the polyfunctional acid halide, and the ratio of the aliphatic amine concentration to the aromatic amine concentration.

[0041] The proportion of coarse pores is calculated by the method described in the section "Proportion of coarse pores" in the Examples below.

[0042] (ii) Carboxy group density In the composite semipermeable membrane according to the second embodiment, the carboxy group density ratio Nd / Nf measured by STEM in a cross section in the thickness direction of the separation functional layer (a cross section perpendicular to the first surface) is 2.1 or less. Here, "Nd" refers to the carboxy group density in region d, and "Nf" refers to the carboxy group density in region f. As shown in FIG. 6, regions d and f are two of regions c to g obtained by dividing the cross section in the thickness direction of the separation functional layer into five equal parts, and the regions are arranged in the order of regions c to g from the first surface to the second surface.

[0043] 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 areas where the carboxyl group density is high, the separation functional layer has a sparse structure. When the separation functional layer has a sparse structure, the water permeation resistance is low, but the solute removal performance is also low. On the other hand, in areas where the carboxyl group density is low, the separation functional layer has a dense structure. When the separation functional layer has a dense structure, the water permeation resistance is high, but the solute removal performance is improved.

[0044] Therefore, by having a gradient structure in which the carboxy group density ratio Nd / Nf of the separation functional layer is 2.1 or less, it is possible to achieve both a particularly high permeate amount and neutral molecule removal performance. From the viewpoint of achieving both a high permeate amount and removal performance, Nd / Nf is preferably 0.1 or more and 1.9 or less, and more preferably 0.2 or more and 1.7 or less.

[0045] As described below in the "Separation functional layer formation process," Nd / Nf can be controlled, for example, by the type and concentration of the aqueous layer additive having an amide group or urea group and the monofunctional amine contained in the polyfunctional amine aqueous solution, the ratio of the concentration of the monofunctional amine to the concentration of the polyfunctional amine, the type and concentration of the polyfunctional acid halide, 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.

[0046] The carboxyl group density of each region is calculated by the method described in the section "Carboxy group density" in the Examples below.

[0047] In the composite semipermeable membrane according to the second embodiment, Nd in the separating functional layer is 2.3 × 10 －２６ mol / nm ２ or less, and Nf is 0.7 × 10 －２６ mol / nm ２ A membrane having a low carboxy group density near the surface has a polyamide structure dense enough to be suitable for removing solutes, and from the viewpoint of improving the membrane's removal ability and ensuring the amount of water permeated through the membrane, Nd is preferably 0.5 × 10 or more. －２６ mol / nm ２ 2.1 x 10 －２６ mol / nm ２ More preferably, 1.0 x 10－２６ mol / nm ２ 1.6 x 10 －２６ mol / nm ２ The following is even more preferred:

[0048] In addition, the membrane with a high carboxyl group density on the inner layer side of the separation functional layer has a polyamide structure that is sparse enough to reduce water permeation resistance, and from the viewpoint of improving the amount of water permeated through the membrane and maintaining the physical strength of the functional layer, Nf is 0.9 × 10 －２６ mol / nm ２ 2.5 x 10 or more －２６ mol / nm ２ More preferably, 1.0 x 10 －２６ mol / nm ２ Above 2.0 x 10 －２６ mol / nm ２ The following is even more preferred:

[0049] As described below in the "Separation functional layer formation process," Nd and Nf can be controlled, for example, by the type and concentration of the aqueous layer additive and monofunctional amine contained in the polyfunctional amine solution, the type and concentration of the polyfunctional acid halide, 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.

[0050] (iii) Amount of terminal amino groups C, amount of terminal carboxy groups D, amount of amide groups E of crosslinked polyamide In the composite semipermeable membrane according to this embodiment, when the amount of terminal amino groups of the crosslinked polyamide in the separation functional layer is C, the amount of terminal carboxy groups is D, and the amount of amide groups is E, it is preferable that E / (C+D) is 1.7 or more. Here, "E / (C+D)" means the ratio of the amount of amide groups to the amount of terminal groups of the crosslinked polyamide contained in the separation functional layer.

[0051] When the amount of amide groups at the crosslinking points is relatively larger than the sum of the amount of terminal amino groups and the amount of carboxyl groups, the density of the separating functional layer is improved, and the solute removal ability and the chemical and physical strength of the separating functional layer are increased. From the above viewpoint and from the viewpoint of ensuring the amount of permeated water, E / (C+D) is more preferably 1.8 or more and 2.2 or less, and even more preferably 1.9 or more and 2.1 or less.

[0052] The amount of terminal amino groups C, the amount of terminal carboxyl groups D, and the amount of amide groups E of the crosslinked polyamide are 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.

[0053] The amount C of terminal amino groups, the amount D of terminal carboxyl groups, and the amount E of amide groups of the crosslinked polyamide can be controlled by, for example, the concentrations of the polyfunctional amine and polyfunctional acid halide monomers, the polymerization time, and the like.

[0054] (iv) Separation Characteristics The composite semipermeable membrane according to this embodiment is suitable for separating non-ionic solutes as well as ionic solutes such as sodium chloride, and is characterized by differences in the removal efficiency of each solute.

[0055] When raw water containing 500 ppm of sodium chloride (hereinafter referred to as "NaCl"), 20 ppm of silica, which is a nonionic neutral molecule, and 1 ppm of boron is passed through the composite semipermeable membrane of this embodiment at an operating pressure of 0.75 MPa, the silica removal rate is preferably 99.30% or more, more preferably 99.45% or more. The boron removal rate of the composite semipermeable membrane is preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. Furthermore, the NaCl removal rate of the composite semipermeable membrane is preferably 99.50% or more, more preferably 99.60% or more, while preferably less than 99.90%. In addition, the difference between the silica removal rate and the NaCl removal rate is preferably 0.20% or less.

[0056] When the silica removal rate, boron removal rate, NaCl removal rate, and the difference between the silica and NaCl removal rates 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.

[0057] In addition, from the viewpoint of reducing the energy consumption when treating raw water with a composite semipermeable membrane, the amount of permeated water under the above conditions is set to 0.70 m ３ / m ２ / day or more is preferable.

[0058] (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.

[0059] 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.

[0060] 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 according to this embodiment only needs to include a porous support layer and a separation functional layer, and may 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."

[0061] 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 of polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, and polyphenylene sulfone are preferred, with cellulose acetate, polysulfone, polyphenylene sulfide sulfone, and polyphenylene sulfone being more preferred. Among these materials, polysulfone is even more preferred due to its high chemical, mechanical, and thermal stability and ease of molding.

[0062] For example, a support membrane can be obtained by dissolving polysulfone in N,N-dimethylformamide (hereinafter referred to as "DMF"), casting a solution of polysulfone onto a tightly woven polyester fabric or a polyester nonwoven fabric to a certain thickness, and then wet-coagulating the resultant in water, thereby obtaining a support membrane having fine pores with diameters of several tens of nanometers or less over the majority of its surface.

[0063] 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 and 300 μm or less, and more preferably 100 μm or more and 220 μm or less.

[0064] 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.

[0065] The thickness of the porous support layer in the composite semipermeable membrane according to this embodiment is preferably 20 μm or more and 100 μm or less. When the thickness of the porous support layer is 20 μm or more, good pressure resistance can be obtained, and a uniform support membrane without defects can be obtained. A composite semipermeable membrane including such a porous support layer exhibits good salt rejection performance. Furthermore, when the thickness of the porous support layer is 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.

[0066] (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.

[0067] 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.

[0068] 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. When the temperature of the polymer solution is within the above range, the polymer does not precipitate, and the polymer solution is sufficiently impregnated into the spaces between the fibers of the substrate before solidifying. As a result, the porous support layer is firmly bonded to the substrate due to the anchoring 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.

[0069] The time from when the polymer solution is applied to the substrate until when the substrate is immersed in the coagulation bath is preferably 0.1 seconds or more and 5 seconds or less. When the time until when the substrate is immersed in the coagulation bath is within the above 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 until when 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.

[0070] Water is generally used as the coagulation bath, but any solution that does not dissolve the polymers that are components of the porous support layer is acceptable, and is not particularly limited. The morphology of the resulting porous support layer changes depending on the composition of the coagulation bath, and thereby the resulting composite semipermeable membrane also changes. The temperature of the coagulation bath is preferably −20°C or higher and 100°C or lower, and more preferably 10°C or higher and 50°C or lower. When the temperature of the coagulation bath is within the above range, the vibration of the coagulation bath surface due to thermal motion does not become severe, and the smoothness of the porous support layer surface after formation of the porous support layer is maintained. Furthermore, when the temperature is within the above range, the coagulation rate is appropriate, and membrane formability is good.

[0071] 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. When the hot water temperature is within the above range, the shrinkage of the support membrane does not increase and the amount of permeated water is good. Furthermore, when the hot water temperature is within the above range, a sufficient washing effect can be obtained.

[0072] (2-2) Separation Functional Layer Formation Process In the method for producing a composite semipermeable membrane according to this embodiment, the separation functional layer is formed by interfacial polycondensation in which a polyfunctional amine aqueous solution and a polyfunctional acid halide solution are brought into contact on a porous support layer. The polyfunctional amine aqueous solution contains a polyfunctional amine, a monofunctional amine having a molecular weight of 150 or less, and an aqueous layer additive having an amide group or a urea group. The polyfunctional acid halide solution contains a polyfunctional acid halide and an organic solvent.

[0073] 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.

[0074] The organic solvent for dissolving the polyfunctional aromatic acid chloride may be any organic solvent that is immiscible with water, does not destroy the support film, and does not inhibit the crosslinked aromatic polyamide production reaction. Representative examples of organic solvents for dissolving the polyfunctional aromatic acid chloride include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. From the viewpoints of non-ozone-depleting substances, ease of availability, ease of handling, and safety in handling, preferred are octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, 1-decene, and the like, either alone or in mixtures thereof.

[0075] In the method for producing a composite semipermeable membrane according to this embodiment, the water content in the organic solvent in which the polyfunctional acid halide is dissolved is preferably 10 ppm or more and 50 ppm or less. By reducing the water content in the organic solvent, the 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. Furthermore, when the water content in the organic solvent in which the polyfunctional acid halide is dissolved is 50 ppm or less, the inhibition of the polycondensation 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 proportion A of coarse pores near the surface of the separation functional layer is small and the proportion B of coarse pores on the inner layer side is large, or the number of carboxy groups near the surface of the separation functional layer is reduced, making it easier to produce a separation functional layer with a small Nd / Nf ratio. For the above reasons, the water content in the organic solvent in which the polyfunctional acid halide is dissolved is more preferably 10 ppm or more and 30 ppm or less.

[0076] The water content in the 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 in this specification, coulometric titration is used.

[0077] In the method for producing a composite semipermeable membrane according to this embodiment, the aqueous polyfunctional amine solution contains a polyfunctional amine, a monofunctional amine having a molecular weight of 150 or less, and an aqueous layer additive having an amide group or a urea group. The presence of a monofunctional amine having a molecular weight of 150 or less during interfacial polycondensation allows the monofunctional amine to diffuse into the polyamide network and react with the terminal carboxy groups in the surface layer, thereby reducing the proportion A of coarse pores near the surface layer of the separation functional layer, or reducing the number of carboxy groups near the surface layer of the separation functional layer. From the viewpoint of sufficient diffusion into the polyamide network, the molecular weight of the monofunctional amine is preferably 120 or less, more preferably 100 or less, and even more preferably 50 or less.

[0078] In the method for producing a composite semipermeable membrane according to this embodiment, the concentration of the monofunctional amine having a molecular weight of 150 or less in the aqueous polyfunctional amine solution is preferably 0.01% by mass to 10% by mass, more preferably 0.05% by mass to 8% by mass. When the concentration of the monofunctional amine is within the above range, the neutral molecule removal performance can be improved without impairing the salt removal performance of the separating functional layer.

[0079] In addition, the presence of an aqueous layer additive having an amide group or urea group in the polyfunctional amine aqueous solution promotes the hydrolysis reaction between the acid chloride and water on the separation functional layer side near the interface, thereby increasing the proportion B of coarse pores in the inner layer portion of the separation functional layer, or increasing the carboxyl group density in the inner layer portion compared to the surface layer portion.

[0080] Examples of aqueous layer additives having an amide group include N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N,N-diethylacetamide, N-methylpyrrolidinone, γ-butyrolactam, and ε-caprolactam.

[0081] Examples of aqueous layer additives having a urea group include urea, dimethylurea, diethylurea, dibutylurea, diphenylurea, tetramethylurea, tetraethylurea, bis(pentamethylene)urea, 2-imidazolidinone, 1,3-dimethyl-2-imidazolidinone, dimethoxymethylurea, diethoxymethylurea, N,N-dimethylpropyleneurea, N,N'-dimethylolurea, dimethylolethyleneurea, dimethyloldihydroxyethyleneurea, dimethylolpropyleneurea, and tetramethylolacetylenediurea.

[0082] In the method for producing a composite semipermeable membrane according to this embodiment, the concentration of the aqueous layer additive in the aqueous polyfunctional amine solution 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. When the concentration of the aqueous layer additive in the aqueous polyfunctional amine solution is within the above range, a separation functional layer can be formed that ensures separation performance and mechanical strength while sufficiently promoting the hydrolysis reaction inside the functional layer.

[0083] To carry out 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 which 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.

[0084] The method for coating the surface of the porous support layer with an aqueous solution of a polyfunctional aromatic amine may be any method that uniformly and continuously coats the surface of the porous support layer with the aqueous solution, and examples thereof include known coating means, such as a method of coating the surface of the porous support layer with the aqueous solution and a method of immersing the porous support layer in the aqueous solution.

[0085] 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, the excess aqueous solution is preferably removed by a draining step. For example, the draining method may involve holding the support membrane surface vertically and allowing the solution to flow naturally. After draining, the support membrane surface may be dried to remove all or part of the water in the aqueous solution.

[0086] The polyfunctional aromatic acid chloride solution is then applied to the porous support layer coated with the polyfunctional aromatic amine aqueous solution, and a crosslinked aromatic polyamide is formed by interfacial polycondensation. 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.

[0087] The concentration of the polyfunctional aromatic acid chloride in the polyfunctional aromatic acid chloride solution 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 cost.

[0088] 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 composite semipermeable membrane is held vertically and the excess organic solvent is removed by gravity flow. 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.

[0089] (3) Use of Composite Semipermeable Membrane The composite semipermeable membrane according to 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.

[0090] 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.

[0091] The temperature of the raw water supplied 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 raw water in the neutral range.

[0092] The module using the composite semipermeable membrane of this embodiment is characterized by its high ability to remove neutral molecules, 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.

[0093] (3-1) Ultrapure Water Production Method The method for producing ultrapure water described below includes, as shown in FIG. 7, a pretreatment step for removing suspended solids from raw water, a primary treatment step (reverse osmosis step) for removing silica from the aqueous solution after the pretreatment step using a reverse osmosis membrane, and a secondary treatment step for removing ionic components from the aqueous solution that has undergone the step using the reverse osmosis membrane.

[0094] In the method for producing ultrapure water according to this embodiment, only the reverse osmosis step is essential, and the other steps are optional. Each of the steps will be described below.

[0095] (3-2) Pretreatment Step (3-2-1) Raw Water The raw water targeted in this embodiment is an aqueous solution containing silica (hereinafter referred to as a "silica-containing aqueous solution" regardless of whether the pretreatment step is performed or not), 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).

[0096] (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 raw water 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 used 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.

[0097] (3-3) Primary Treatment Step (Reverse Osmosis Step) (3-3-1) Reverse Osmosis Membrane (RO Membrane) The ultrapure water production method 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 ultrapure water production method of this embodiment includes a step in which silica is separated and removed from raw water or an aqueous solution treated in a pretreatment step using the composite semipermeable membrane of this embodiment as a reverse osmosis membrane in a primary treatment step. The high permeate flow rate of the reverse osmosis membrane allows for high-recovery operation without increasing the operating pressure, reducing the amount of concentrated water (waste water), thereby achieving a highly efficient process. Furthermore, the high silica removal rate of the reverse osmosis membrane allows for a reduced silica concentration in the aqueous solution supplied from the primary treatment step to the secondary treatment step described below. This prevents silica precipitation on the surface of the ion exchange resin used in the secondary treatment step, and thereby reduces the treatment efficiency of the secondary treatment step and deterioration of the ion exchange resin.

[0098] (3-3-2) Operating 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 to 12 MPa. A pressure of 0.10 MPa or higher can prevent a decrease in the membrane permeation rate of water, and a pressure of 12 MPa or lower can reduce the possibility of damaging the membrane. From the above viewpoints, the pressure at which raw water or a pretreated aqueous solution is supplied is more preferably 0.25 MPa to 6 MPa, and even more preferably 0.25 MPa to 1 MPa. When the amount of water permeated through the reverse osmosis membrane is 0.85 m ３ / m ２ / day or more, it is possible to obtain a sufficient amount of permeate even under low-pressure operation of 1 MPa or less, which reduces the energy consumption per unit amount 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.

[0099] 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 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.

[0100] (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 permeate obtained in the primary treatment step to produce ultrapure water. The secondary treatment step preferably uses an ion exchange resin (hereinafter also referred to as an "ion exchanger").

[0101] 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 desalination 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 desalinates (deionizes) 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.

[0102] Furthermore, the secondary treatment step may include UV treatment.

[0103] The present invention will be described below with reference to examples, but the present invention is not limited to these examples in any way.

[0104] <Water content of organic solvent> The water content of the organic solvent before dissolving the polyfunctional acid halide was measured by Karl Fischer coulometric titration using a trace water content analyzer (CA-200 manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0105] <Solute Removal Rate> Raw 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 to perform membrane filtration. The membrane area of ​​the composite semipermeable membrane was 33 cm ２ Two hours after the start of membrane filtration, the permeated water was sampled for 20 minutes. The electrical conductivity of the raw water and permeated water 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 removal rate was calculated from the obtained NaCl concentrations based on the following formula. Here, NaCl concentration (ppm) means the concentration on a mass basis. NaCl removal rate (%) = 100 × {1 - (NaCl concentration in permeated water / NaCl concentration in raw water)}

[0106] The silica and boron concentrations in the raw water and permeated 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 permeated water / silica concentration in raw water)} Boron removal rate (%) = 100 × {1 - (boron concentration in permeated water / boron concentration in raw water)}

[0107] <Permeate volume> In the above-mentioned "solute removal rate" test, the amount of raw water that passes through the membrane is measured, and the value converted to the amount of water that passes through the membrane per square meter of membrane surface per day (cubic meters) is called the permeate volume (m ３ / m ２ / day).

[0108] <Proportion of Coarse Pores> A 5 ​​cm square composite semipermeable membrane from which the substrate had been physically peeled was processed by cryo-ultrathin sectioning, placed on a copper grid, and immersed in pure water for 4 hours, followed by immersion in a 10% by mass aqueous 2-propanol solution for 1 hour for washing. The moisture in the sample was then removed with filter paper and freeze-dried to obtain a measurement sample. The prepared measurement sample was photographed using a field emission transmission electron microscope (HF5000 manufactured by Hitachi High-Tech) at an accelerating voltage of 200 kV, and a STEM image at a magnification of 100,000 was obtained. The obtained image was then analyzed using image processing software. As shown in FIG. 5, a reference point P was determined on the outer surface 26 of the separation functional layer (the surface facing away from the porous support layer) in a random region within 50-100% of the height of each convex portion in the pleated structure of the separation functional layer. A normal line V0 passing through the reference point P was used as the center, and straight lines V1 and V2 parallel to the normal line V0 were drawn on both sides of the normal line V0 at intervals of 3-10 nm. A tangent line Z1 to the outer surface of the separation functional layer passing through the reference point P, and a tangent line Z2 to the inner surface 25 of the separation functional layer (the surface in contact with the porous support layer) parallel to the normal line V1, were drawn. A line Z3 was drawn between Z1 and Z2, dividing the distance between Z1 and Z2 into two equal parts. The regions surrounded by V1 and V2, and also surrounded by Z1, Z2, and the line Z3 between them, were designated region a and region b, respectively, from the outer surface side of the separation functional layer. The areas of region a and region b were 10 nm. ２ More than 80 nm ２ The following was determined. Furthermore, the STEM image was deconvolved using DeConvHAADF (HREM research inc.) to highlight the pore and polyamide structure. Next, binarization was performed using ImageJ, and particle size analysis was performed to quantitatively analyze the number of pores and pore diameter in each region. From this analysis, the pore diameter and area for each pore were calculated as the number of pixels in the image. From the calculated pore diameter and pore area, the proportions A and B of coarse pores with a pore diameter of 0.7 nm or more in regions a and b were calculated using the following formula. The average value of the proportions of coarse pores obtained for five convex portions of the separation functional layer was used as the proportion of coarse pores in each region. Proportion A of coarse pores = total number of pixels of coarse pores in region a / total number of pixels of all pores in region a Proportion B of coarse pores = total number of pixels of coarse pores in region b / total number of pixels of all pores in region b

[0109] <Carboxy group density> A 5 ​​cm square composite semipermeable membrane from which the substrate was physically peeled was treated by cryo-ultrathin sectioning, placed on a copper 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, a 1.0 × 10 －３ The sample was immersed in a 1.0 × 10 mol / L barium chloride aqueous solution for 10 minutes three times in total, followed by a 1.0 × 10 mol / L barium chloride aqueous solution adjusted to pH 3.8 and 25°C. －７ The sample was immersed in a 1000 mol / L barium chloride aqueous solution for 7 minutes, a total of four times. The sample was then dehydrated with filter paper and freeze-dried to obtain a measurement sample. The prepared measurement sample was photographed using a field-emission transmission electron microscope (HF5000, manufactured by Hitachi High-Technologies) at an accelerating voltage of 200 kV, and a 100,000-magnification STEM image was obtained. Then, as shown in Figure 6, a reference point P was set on the outer surface 26 of the separation functional layer (the surface facing away from the porous support layer) in a random region within 50-100% of the height of each convex portion in the pleated structure of the separation functional layer. Centered on the normal line V0 passing through the reference point P, straight lines V1 and V2 parallel to the normal line V0 were drawn on both sides of the normal line V0 at intervals of 3-10 nm. A tangent line Z1 to the outer surface of the separator layer passing through the reference point P and a tangent line Z2 parallel to the inner surface 25 of the separation functional layer (the surface in contact with the porous support layer) were also drawn. Between Z1 and Z2, four straight lines were drawn to divide this interval into five equal parts. The regions surrounded by V1 and V2 and also surrounded by Z1, Z2 and the lines between them were designated regions c to g in order from the first surface side of the composite semipermeable membrane. The area of ​​each of regions c to g was 5 nm ２ 30nm or more ２ The obtained image was analyzed using image processing software, and the brightness was measured by STEM in the above-mentioned regions c to g. The area of ​​the portions showing a brightness of {Lmin + (Lmax - Lmin) / 3} or more at the minimum brightness Lmin and maximum brightness Lmax of the measured values ​​was integrated for each region. This integrated value means the total area of ​​the portions having carboxy groups labeled with barium (Ba). The obtained integrated value was calculated as the area per molecule of carboxy groups (0.04 nm ２ ), Avogadro's constant (6.0 x 10 ２３The carboxyl group density (mol / nm ２ The average value of the carboxy group density measured for five randomly selected convex portions of the separation functional layer was taken as the carboxy group density of each region.

[0110] <Amount of terminal amino group C, amount of terminal carboxy group D, amount of amide group E> 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 in small amounts 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 no elution of the polymer that forms the porous support layer could 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.

[0111] <Contact Angle> The static contact angle was automatically calculated by computer image analysis using the θ / 2 method using a Drop Master DM500 manufactured by Kyowa Interface Science Co., Ltd. The droplet volume was 1.5 μl, and the static contact angle was measured 10 seconds after the distilled water droplet landed on the separation functional layer.

[0112] [Example 1] Polyester nonwoven fabric made of long fibers (breathability 2.0 cc / cm ２A 15.0 mass% DMF solution of polysulfone was cast onto the porous support layer (a 40 μm thick support membrane) 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 polyfunctional amine aqueous solution containing 2.0 mass% m-PDA as a polyfunctional amine, 0.1 mass% ethylamine as a monofunctional amine with a molecular weight of 150 or less, and 1.2 mass% DMF as an aqueous layer additive, and then excess aqueous solution was removed. Furthermore, a polyfunctional acid halide solution prepared using n-decane with a water content of 40 ppm and a TMC concentration of 0.10 mass% as a polyfunctional acid halide was added at a rate of 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 using a blower.

[0113] Example 2 A composite semipermeable membrane of Example 2 was obtained in the same manner as in Example 1, except that ε-caprolactam (hereinafter, referred to as “εCL”) was used as the aqueous layer additive.

[0114] Example 3 A composite semipermeable membrane of Example 3 was obtained in the same manner as in Example 1, except that N,N'-dimethylpropyleneurea (hereinafter, "DMPU") was used as the aqueous layer additive.

[0115] Example 4 A composite semipermeable membrane of Example 4 was obtained in the same manner as in Example 1, except that the concentration of ethylamine was set to 0.2% by mass.

[0116] Example 5 A composite semipermeable membrane of Example 5 was obtained in the same manner as in Example 1, except that aniline was used as the monofunctional amine and tetramethylurea (hereinafter, "TMU") was used as the aqueous layer additive.

[0117] Example 6 A composite semipermeable membrane of Example 6 was obtained in the same manner as in Example 1, except that methylamine was used as the monofunctional amine and the concentration of DMF was 2.0% by mass.

[0118] Example 7 A composite semipermeable membrane of Example 7 was obtained in the same manner as in Example 1, except that methylamine was used as the monofunctional amine and the water content of n-decane was set to 20 ppm.

[0119] Example 8 A composite semipermeable membrane of Example 8 was obtained in the same manner as in Example 7, except that the water content of n-decane was set to 80 ppm.

[0120] Example 9 A composite semipermeable membrane of Example 9 was obtained in the same manner as in Example 1, except that heptylamine was used as the monofunctional amine.

[0121] Comparative Example 1 A composite semipermeable membrane of Comparative Example 1 was obtained in the same manner as in Example 1, except that ethylamine and DMF were not added to the aqueous polyfunctional amine solution.

[0122] Comparative Example 2 A composite semipermeable membrane of Comparative Example 2 was obtained in the same manner as in Example 1, except that DMF was not added to the aqueous polyfunctional amine solution.

[0123] Comparative Example 3 A composite semipermeable membrane of Comparative Example 3 was obtained in the same manner as in Example 1, except that ethylamine was not added to the aqueous polyfunctional amine solution.

[0124] Comparative Example 4 A composite semipermeable membrane of Comparative Example 4 was obtained in the same manner as in Example 1, except that ethylamine was replaced with 1,3,5-triaminobenzene (hereinafter referred to as "TAB"), which is a polyfunctional amine.

[0125] Comparative Example 5 A composite semipermeable membrane of Comparative Example 5 was obtained in the same manner as in Comparative Example 1, except that the concentration of m-PDA was changed to 3.0% by mass and the concentration of TMC was changed to 0.165% by mass.

[0126] [Comparative Example 6] A composite semipermeable membrane of Comparative Example 6 was obtained in the same manner as in Example 1, except that DMF was not added to the aqueous polyfunctional amine solution, and 0.10 mass% of DMF was added as an organic layer additive to the polyfunctional acid halide solution.

[0127] [Comparative Example 7] A composite semipermeable membrane of Comparative Example 7 was obtained in the same manner as in Comparative Example 1, except that 1.2 mass% of εCL was added to the polyfunctional amine aqueous solution as an aqueous layer additive, and 0.10 mass% of DMF was added to the polyfunctional acid halide solution as an organic layer additive.

[0128] The structures and performances of the composite semipermeable membranes obtained in Examples 1 to 9 and Comparative Examples 1 to 7 are shown in Table 1.

[0129]

[0130] As described above, it can be seen that the composite semipermeable membranes of Examples 1 to 9 in which A / B is 1.40 or less or Nd / Nf is 2.1 or less achieve both a high permeation rate and the ability to remove neutral molecules.

[0131] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and various modifications and substitutions can be made to the above-described embodiment without departing from the scope of the present invention.

[0132] This application is based on a Japanese patent application filed on March 26, 2024 (Patent Application No. 2024-049332) and a Japanese patent application filed on March 26, 2024 (Patent Application No. 2024-049342), the entire contents of which are incorporated by reference.

[0133] 1 Composite semipermeable membrane 2 Substrate 3 Porous support layer 4 Separation functional 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 separation functional layer 26 Outer surface of separation functional layer 27 Pleated thickness 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 line to the outer surface of the separation functional layer passing through reference point P Z2 Tangent line to the inner surface of the separation functional layer parallel to tangent line Z1 Z3 Straight line bisecting the distance between Z1 and Z2

Claims

1. A composite semipermeable membrane having a porous support layer and a separation functional layer located on the porous support layer, wherein the surface of the composite semipermeable membrane has a first side which is the side of the porous support layer on which the separation functional layer is located, and a second side which is the side opposite to the first side, wherein the separation functional layer contains crosslinked polyamide, and wherein a cross section of the separation functional layer in the thickness direction observed with a scanning transmission electron microscope is divided into two equal parts, a region a on the side of the first side and a region b on the side of the second side, and wherein A is the proportion of coarse pores with a pore diameter of 0.7 nm or more in region a and B is the proportion of coarse pores with a pore diameter of 0.7 nm or more in region b, and A / B is 1.40 or less.

2. The composite semipermeable membrane according to claim 1, wherein the proportion A of coarse pores is 0.10 or less.

3. A composite semipermeable membrane having a porous support layer and a separation functional layer located on the porous support layer, wherein the surface of the composite semipermeable membrane has a first side which is the side of the porous support layer on which the separation functional layer is located, and a second side which is the side opposite to the first side, the separation functional layer contains crosslinked polyamide, and the ratio Nd / Nf of carboxy group densities measured by a scanning transmission electron microscope in a cross section in the thickness direction of the separation functional layer is 2.1 or less. Nd: carboxy group density of region d Nf: carboxy group density of region f Regions d and f: regions included in regions c to g obtained by dividing the cross section in the thickness direction of the separation functional layer into five equal parts in the thickness direction of the separation functional layer, and regions c to g are aligned from the first side toward the second side.

4. The Nd is 2.3 × 10 －２６ mol / nm ２ or less, and the Nf is 0.7 × 10 －２６ mol / nm ２ The composite semipermeable membrane according to claim 3 .

5. The composite semipermeable membrane according to any one of claims 1 to 4, wherein E / (C+D) is 1.7 or more, where C is the amount of terminal amino groups in the crosslinked polyamide, D is the amount of terminal carboxyl groups, and E is the amount of amide groups.

6. The composite semipermeable membrane according to any one of claims 1 to 4, wherein the static contact angle of water on the surface of the separating functional layer is 40 degrees or more and 120 degrees or less.

7. A composite semipermeable membrane element comprising the composite semipermeable membrane according to any one of claims 1 to 4.

8. A composite semipermeable membrane module comprising the composite semipermeable membrane element according to claim 7.

9. A method for producing a composite semipermeable membrane comprising a support membrane having a substrate and a porous support layer, and a separation functional layer provided on the porous support layer, wherein the separation functional layer is formed by interfacial polycondensation in which an aqueous polyfunctional amine solution and a polyfunctional acid halide solution are brought into contact on the porous support layer, the aqueous polyfunctional amine solution containing a polyfunctional amine, a monofunctional amine having a molecular weight of 150 or less, and an aqueous phase additive having an amide group or a urea group, and the polyfunctional acid halide solution containing a polyfunctional acid halide and an organic solvent.

10. The method for producing a composite semipermeable membrane according to claim 9, wherein the molecular weight of the monofunctional amine is 100 or less.

11. The method for producing a composite semipermeable membrane according to claim 9 or 10, wherein the water content in the organic solvent is 10 ppm or more and 50 ppm or less.

12. The method for producing a composite semipermeable membrane according to claim 9 or 10, wherein the concentration of the monofunctional amine in the aqueous polyfunctional amine solution is 0.01% by mass or more and 10% by mass or less.

13. The method for producing a composite semipermeable membrane according to claim 9 or 10, wherein the concentration of the aqueous phase additive in the aqueous polyfunctional amine solution is 0.01% by mass or more and 10% by mass or less.

14. 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 according to any one of claims 1 to 4.

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