Composite semipermeable membrane and method for manufacturing the 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

[Technical Field]

[0001] The present invention relates to a composite semipermeable membrane useful for the selective separation of liquid mixtures and to 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. Furthermore, the present invention relates to a method for producing ultrapure water using the composite semipermeable membrane. [Background technology]

[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, the use of membrane separation methods has been expanding as a process for saving energy and resources.

[0003] Examples of membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes are used, for example, in the production of drinking water or industrial ultrapure water from seawater, brine, or water containing harmful substances, as well as in wastewater treatment and the recovery of valuable materials.

[0004] Most reverse osmosis and nanofiltration membranes currently on the market are composite semipermeable membranes. In particular, composite semipermeable membranes obtained by coating a separation functional layer made of a crosslinked aromatic polyamide obtained by the polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide onto a microporous support membrane (Patent Document 1) are widely used as separation membranes with high water-producing properties and high selective separation of salts and neutral molecules. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2010 / 096563 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when removing neutral molecules contained in raw water using a conventional composite semipermeable membrane, its water production performance and selective separation performance are not sufficient, and there are problems with the membrane performance.

[0007] Therefore, an object of the present invention is to provide a composite semipermeable membrane excellent in water permeation amount and removal property of neutral molecules.

Means for Solving the Problems

[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, The surface of the composite semipermeable membrane has a first surface which is the surface in the direction of the side where the separation functional layer exists with respect to the porous support layer, and a second surface which is the surface on the opposite side of the first surface, The separation functional layer contains crosslinked polyamide, When the cross-sectional view in the thickness direction of the separation functional layer observed by a scanning transmission electron microscope is divided into two equal parts into a region a on the first surface side and a region b on the second surface side, and the ratio A of the large pores having a pore diameter of 0.7 nm or more in the region a and the ratio B of the large pores having a pore diameter of 0.7 nm or more in the region b are defined, a composite semipermeable membrane in which A / B is 1.40 or less. [2] The composite semipermeable membrane according to [1], wherein the ratio A of the large 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, The surface of the composite semipermeable membrane has a first surface which is the surface in the direction of the side where the separation functional layer exists with respect to the porous support layer, and a second surface which is the surface on the opposite side of the first surface, The separation functional layer contains crosslinked polyamide, A composite semipermeable membrane in which the ratio Nd / Nf of the carboxy group density measured by a scanning transmission electron microscope in the cross-sectional view in the thickness direction of the separation functional layer is 2.1 or less. Nd: Carboxy group density in region d Nf: Carboxy group density in region f Regions d and f are regions included in regions c to g obtained by dividing the cross-section of the separation functional layer in the thickness direction 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] The above Nd is 2.3 × 10 -26 mol / nm 2 The following applies, and the above Nf is 0.7 × 10 -26 mol / nm 2 The above is the composite semipermeable membrane described in [3] above. [5] A composite semipermeable membrane according to any one of [1] to [4] above, wherein when the number of terminal amino groups of the crosslinked polyamide is C, the number of terminal carboxyl groups is D, and the number of amide groups is E, E / (C+D) is 1.7 or more. [6] A 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 any one of the composite semipermeable membranes described in [1] to [6] above. [8] A composite semipermeable membrane module comprising the composite semipermeable membrane element described in [7] above. [9] A method for manufacturing a composite semipermeable membrane comprising a substrate and a support membrane having a porous support layer, and a separation functional layer provided on the porous support layer, The above 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 the porous support layer. The above polyfunctional amine aqueous solution comprises a polyfunctional amine, a monofunctional amine with a molecular weight of 150 or less, and an aqueous layer additive having an amide group or a urea group. The above polyfunctional acid halide solution is a method for producing a composite semipermeable membrane, comprising a polyfunctional acid halide and an organic solvent.

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

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

[10] above, wherein the water content of 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] , wherein the concentration of the monofunctional amine in the polyfunctional amine aqueous solution is 0.01% by mass or more and 10% by 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 layer additive in the polyfunctional amine aqueous 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 a composite semipermeable membrane described in any one of [1] to [6] above. [Effects of the Invention]

[0009] According to the present invention, a composite semipermeable membrane can be obtained that achieves both high permeability and removal efficiency of medium-sized molecules. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram showing a cross-section of a composite semipermeable membrane according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing a cross-section of the pleated structure in the separation functional layer. [Figure 3] Figure 3 is a schematic diagram illustrating the method for measuring the average surface roughness at 10 points. [Figure 4] Figure 4 is a schematic diagram showing the state when water is dropped onto the surface of the separation functional layer. [Figure 5] Figure 5 is a schematic diagram showing regions a and b in the cross-section in the thickness direction of the separation functional layer. [Figure 6] Figure 6 is a schematic diagram showing regions c, d, e, f, and g in the cross-section in the thickness direction of the separation functional layer. [Figure 7] Figure 7 is a flow chart showing the steps of an ultrapure water production method, which is one embodiment of the present invention. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described in detail below, but the present invention is not limited in any way thereto. In this specification, "mass" is synonymous with "weight."

[0012] (1) Composite semipermeable membrane As shown in Figure 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. Furthermore, of the surfaces of the composite semipermeable membrane 1, the surface in the direction on which the separation function layer 4 exists relative to the porous support layer 3 is referred to as the first surface 11, and the surface on the opposite side of the first surface is referred to as the second surface 12.

[0013] The composite semipermeable membrane according to this embodiment includes a first embodiment that satisfies condition 1 below and a second embodiment that satisfies condition 2 below. Condition 1: The separation functional layer has a ratio of A / B (compared to the proportion of coarse pores), which will be described later, of 1.40 or less. Condition 2: The separation functional layer has a carboxyl group density of 2.1 or less, with an Nd / Nf ratio described later.

[0014] In all embodiments of the composite semipermeable membrane, the polyamide structure near the surface of the separation functional layer is denser than the polyamide structure of the inner layer to a certain extent, resulting in excellent permeable water volume and removal of neutral molecules. The composite semipermeable membrane according to this embodiment only needs to satisfy at least one of conditions 1 and 2, and may satisfy both. Furthermore, in this specification, "composite semipermeable membrane according to this embodiment" includes both the first and second embodiments unless otherwise specified.

[0015] (1-1) Separation functional layer (1-1-1) Composition Of the components of the composite semipermeable membrane, the separation functional layer is the one that substantially possesses solute separation capabilities. In the cross-sectional view of the composite semipermeable membrane shown in Figure 1, the separation functional layer 4 is arranged 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" means a polycondensate of a polyfunctional amine and a polyfunctional acid halide. Because of its high chemical stability against acids and alkalis, it is preferable for the separation functional layer to contain a crosslinked polyamide as the main component. Here, "main component" means a component that makes up 50% by mass or more of the components constituting the substance.

[0017] Crosslinked polyamides are preferably formed by interfacial polycondensation between a polyfunctional amine and a polyfunctional acid halide. Furthermore, it is preferable that at least one of the polyfunctional amine and the polyfunctional acid halide contains a trifunctional or greater compound.

[0018] A "polyfunctional amine" refers to an amine that has at least two primary amino groups and / or secondary amino groups in one molecule, with at least one of those amino groups being 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 in an ortho, meta, or para position; or 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] In particular, from the viewpoint of the removal performance, permeable water volume, and heat resistance of the composite semipermeable membrane, polyfunctional aromatic amines having 2 to 4 primary amino groups and / or secondary amino groups in one molecule are preferred. Examples of such polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene. Among these, m-phenylenediamine (hereinafter, "m-PDA") is more preferred due to its availability and ease of handling.

[0020] These polyfunctional amines may be used individually or in combination of two or more. When two or more are used simultaneously, the amines may be combined with each other, or they 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] A "polyfunctional acid halide" refers to an acid halide having at least two halogenated carbonyl groups in one molecule. Examples of trifunctional acid halides include trimesic acid chloride (hereinafter referred to as "TMC"), 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride. Examples of difunctional acid halides include aromatic difunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic difunctional acid halides such as adipoyl chloride and sebacoyl chloride; or alicyclic difunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofrancicarboxylic acid dichloride.

[0022] From the viewpoint of reactivity with polyfunctional amines, polyfunctional acid halides are preferably polyfunctional acid chlorides. Furthermore, from the viewpoint of the removal performance and heat resistance of the composite semipermeable membrane, polyfunctional aromatic acid chlorides having 2 to 4 carbonyl chloride groups in one molecule are more preferred. Among these, TMC is even more preferred from the viewpoint of ease of availability and ease of handling. These polyfunctional acid halides may be used individually 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. A "pleated structure" means a structure in which the protruding parts shown in Figure 2 are repeated. Here, a "protrusion" means the space between the vertices of adjacent parts that are convex toward the porous support layer (concave parts of the separation functional layer) in the pleated structure of the separation functional layer as shown in Figure 2. The ends of the protrusions (vertices of the concave parts) may have one end separated from the surface of the porous support layer and the other 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 to 20.0 nm, and more preferably 9.0 nm to 13.0 nm, from the viewpoint of obtaining sufficient separation performance and permeable water volume.

[0025] The pleat thickness can be controlled by, for example, the concentration of the monomer polyfunctional amine and polyfunctional acid halide, and the amount of polyfunctional acid halide solution applied relative to the surface area of ​​the porous support layer, as described in the "Formation Process of the Separation Functional Layer" below.

[0026] The fold thickness can be measured by taking a cross-sectional image of the fold structure with a transmission electron microscope (TEM) and then reading the cross-sectional image into image analysis software for analysis. Specifically, five convex parts are randomly selected from the TEM image of the cross-section of the separation functional layer. At each convex part (indicated by symbols 21 and 22 in Figure 2), the fold thickness (indicated by symbol 27 in Figure 2) is measured at 10 points within the region from the apex of the convex part up to 90% of its height (indicated by symbols 23 and 24 in Figure 2, hereinafter also referred to as "convex height"). In other words, as shown in Figure 2, the surface of the porous support layer is set to a height of 0%, and the apex of the convex part to a height of 100%, and 10 measurement points are randomly selected within the range of 10% to 100% height. The arithmetic mean value calculated from the thicknesses of these 50 points is the "fold thickness". Here, the convex parts to be measured when calculating the fold thickness are those that have a height of at least one-fifth of the average surface roughness of the 10 points.

[0027] The 10-point average surface roughness is calculated as follows: The cross-section of the separation functional layer in the thickness direction is observed using an electron microscope. A magnification of 10,000 to 100,000 times is preferable. As shown in Figure 3, the surface of the separation functional layer 4 appears as a pleated curve with continuously repeating convex and concave portions in the obtained cross-sectional image. A roughness curve defined according to JIS B 0601:2013 (ISO 4287:1997) is determined for this curve. A cross-sectional image is extracted with a width of 2.0 μm, using the average line X of the above roughness curve as the reference length L. From this sampled area, the average of the absolute values ​​of the elevations of the top five peaks (Yp1-5) on the roughness curve, starting from the highest peak, is calculated, and the sum of the average of the absolute values ​​of the elevations of the bottom five valleys (Yv1-5) starting from the lowest valley is calculated. This value, expressed in nanometers (nm), is the 10-point average surface roughness. The mean line is a straight line defined according to ISO 4287:1997, and it refers to a straight line drawn such that, over a measurement length L, the sum of the areas enclosed by the mean line and the roughness curve is equal above and below the mean line.

[0028] From the viewpoint of obtaining a sufficient amount of permeable water, the intermediate value of the height of the protrusions in the separation functional layer of the composite semipermeable membrane according to this embodiment is preferably 80 nm to 300 nm, more preferably 120 nm to 300 nm, and even more preferably 160 nm to 300 nm.

[0029] The median value of the protrusion height is calculated as follows: In a composite semipermeable membrane, when 10 cross-sections are observed at random, the protrusion height of all protrusions that are at least one-fifth of the average surface roughness of the 10 points mentioned above is measured in each cross-section. Furthermore, the median value of the protrusion height 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 average line of the roughness curve mentioned above.

[0030] The height of the protrusions in the separation functional layer can be controlled, for example, by adjusting the diffusivity of the polyfunctional amine into the organic layer, such as by adding an additive that interacts with the polyfunctional amine through hydrogen bonding to the aqueous or organic layer during the formation process of the separation functional layer.

[0031] The static contact angle of water on the surface of the separation 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 representing the wettability and hydrophilicity of the surface of the separation functional layer, and the smaller the contact angle, the higher the hydrophilicity. In the composite semipermeable membrane according to this embodiment, the reaction of the monofunctional amine near the surface layer of the separation functional layer reduces the ratio of the large pores in the surface layer, or reduces the carboxyl group density in the surface layer, and improves the hydrophobicity. From the perspective of achieving both the water permeation rate and the removal performance 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 FIG. 4, when water is dropped onto the surface of the separation functional layer, the water becomes round due to surface tension, and the following formula (1), called the "Young's formula", holds. γ S =γ L cosθ + γ SL ··· Formula (1) Here, γ S is the surface tension of the separation functional layer, γ L is the surface tension of water, and γ SL is the interfacial tension between the separation functional layer and water. The angle θ formed by the tangent of water when the above formula (1) is satisfied and the surface of the separation functional layer is defined as the static contact angle of water. Since the static contact angle gradually changes to a smaller value over time, the value 10 seconds after the water drops onto the surface of the separation functional layer is defined as the static contact angle of water.

[0033] (1-1-2) Characteristics

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

[0035] A separation functional layer, primarily composed of crosslinked polyamide formed by interfacial polycondensation, has pores within the polyamide chains and polyamide network structure that allow water molecules or solute molecules to permeate. If we define coarse pores as those with a diameter of 0.7 nm or larger, a high proportion of coarse pores in a region indicates a sparse structure of the separation functional layer. A sparse structure results in low water permeability resistance, but also low solute removal performance. Conversely, a low proportion of coarse pores in a region indicates a dense structure of the separation functional layer. A dense structure results in high water permeability resistance, but also high solute removal performance.

[0036] The inventors have found that a separation functional layer satisfying an A / B ratio of 1.40 or less can achieve both a particularly high permeate volume and the ability to remove neutral molecules. From the viewpoint of achieving both a high permeate volume and the ability to remove neutral molecules, an A / B ratio of 0.10 to 1.40 is preferred, 0.80 to 1.35 is more preferred, 1.00 to 1.30 is even more preferred, and 1.10 to 1.30 is particularly preferred.

[0037] As described in the "Separation Functional Layer Formation Process" below, A / B can be controlled by, for example, 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 this embodiment, the composite semipermeable membrane preferably has a proportion A of coarse pores in region a of 0.10 or less. A composite semipermeable membrane with a small proportion of coarse pores near the surface of the separation functional layer, i.e., a composite semipermeable membrane with a small value of A, has a polyamide structure that is sufficiently dense for solute removal, and the removal performance of the composite semipermeable membrane is improved. From the viewpoint of balancing the removal performance and permeate volume of the composite semipermeable membrane, A is more preferably 0.01 to 0.10, and even more preferably 0.03 to 0.08.

[0039] Furthermore, composite semipermeable membranes with a large proportion of coarse pores on the inner layer side of the separation functional layer, i.e., composite semipermeable membranes with a large value for the proportion of coarse pores B in region b, have a polyamide structure that is suitable for reducing water permeability resistance, and the amount of water permeate through the composite semipermeable membrane is improved. On the other hand, from the viewpoint of maintaining the physical strength of the separation functional layer, B is preferably 0.01 to 0.20, more preferably 0.03 to 0.18, and even more preferably 0.05 to 0.15.

[0040] A and B can be controlled, as described in the "Separation Functional Layer Formation Process" below, by, for example, 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 using the method described in "Proportion of Coarse Pores" in the examples described later.

[0042] (ii) Carboxy group density In the composite semipermeable membrane according to the second embodiment, the ratio of carboxyl group densities 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 carboxyl group density of region d, and "Nf" refers to the carboxyl group density of region f. Regions d and f are two of the regions c to g obtained by dividing the cross-section in the thickness direction of the separation functional layer into five equal parts, as shown in Figure 6, and each region is arranged in the order of regions c to g from the first surface toward the second surface.

[0043] The separation functional layer, primarily composed of crosslinked polyamide formed by interfacial polycondensation, has amino and carboxyl groups as terminal functional groups. In regions with high carboxyl group density, the separation functional layer has a sparse structure. A sparse structure results in low water permeability resistance, but also low solute removal performance. Conversely, in regions with low carboxyl group density, the separation functional layer has a dense structure. A dense structure results in high water permeability resistance, but also high solute removal performance.

[0044] Therefore, by having a gradient structure in which the carboxyl 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 volume and neutral molecule removal performance. From the viewpoint of balancing permeate volume and removal performance, an Nd / Nf ratio of 0.1 to 1.9 is preferred, and 0.2 to 1.7 is more preferred.

[0045] The Nd / Nf ratio can be controlled by, for example, the type and concentration of the aqueous layer additive having an amide 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, as described in the "Separation Functional Layer Formation Process" below.

[0046] The carboxyl group density in each region is calculated using the method described in "Carboxyl Group Density" in the examples below.

[0047] The composite semipermeable membrane according to the second embodiment has an Nd content of 2.3 × 10 in the separation functional layer. -26 mol / nm 2 The following applies, and Nf is 0.7 × 10⁻⁶ -26 mol / nm 2 The above is preferable. A membrane with a low carboxyl group density near the surface has a polyamide structure that is dense enough to be suitable for solute removal, and from the viewpoint of improving the membrane's removeability and ensuring the amount of water permeate the membrane, Nd should be 0.5 × 10⁻⁶. -26 mol / nm 2 The above 2.1 × 10-26 mol / nm 2 The following is more preferable: 1.0 × 10 -26 mol / nm 2 The above 1.6 × 10 -26 mol / nm 2 The following are even more preferable.

[0048] Furthermore, membranes with a high carboxyl group density on the inner layer side of the separation functional layer have a polyamide structure that is suitable for reducing water permeability resistance, and from the viewpoint of improving the amount of water permeate through the membrane and maintaining the physical strength of the functional layer, Nf is 0.9 × 10⁻⁶. -26 mol / nm 2 The above 2.5 × 10 -26 mol / nm 2 The following is more preferable: 1.0 × 10 -26 mol / nm 2 The above 2.0 × 10 -26 mol / nm 2 The following are even more preferable.

[0049] Nd and Nf can be controlled, as described in the "Separation Functional Layer Formation Process" below, by, for example, the type and concentration of aqueous layer additives and monofunctional amines contained in the polyfunctional amine solution, the type and concentration of polyfunctional acid halides, the water content in the organic solvent that dissolves the polyfunctional acid halides, and the amount of polyfunctional acid chloride solution applied relative to the surface area of ​​the porous support layer.

[0050] (iii) Number of terminal amino groups C, number of terminal carboxyl groups D, and number of amide groups E of the cross-linked polyamide In this embodiment, the composite semipermeable membrane preferably has an E / (C+D) ratio of 1.7 or higher, where C is the amount of terminal amino groups, D is the amount of terminal carboxyl groups, and E is the amount of amide groups in the crosslinked polyamide in the separation functional layer. Here, "E / (C+D)" means the ratio of the amount of amide groups to the amount of terminal groups in the crosslinked polyamide contained in the separation functional layer.

[0051] When the number of amide groups, which are the crosslinking points, is relatively greater than the sum of the number of terminal amino groups and carboxyl groups, the density of the separation functional layer is improved, and the solute removal efficiency and the chemical and physical strength of the separation functional layer are enhanced. From the above viewpoint and from the viewpoint of ensuring the amount of permeate, 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, terminal carboxyl groups D, and amide groups E of the cross-linked polyamide are determined in the separation functional layer. 13 C solid-state nuclear magnetic resonance measurement (hereinafter referred to as “ 13 This can be calculated by "13C solid-state NMR measurement". Specifically, the substrate is peeled from the composite semipermeable membrane to obtain the separation functional layer and the porous support layer, and then the porous support layer is removed by dissolving it to obtain the separation functional layer. The obtained separation functional layer is then measured by the DD / MAS method. 13 Solid-state NMR measurements are performed, and the ratios are calculated by comparing the integral values ​​of the carbon peaks of each functional group or the carbon peaks to which each functional group is attached.

[0053] The number of terminal amino groups C, terminal carboxyl groups D, and amide groups E of the crosslinked polyamide can be controlled, for example, by the concentration of the monomer polyfunctional amine and polyfunctional acid halide, the polymerization time, etc.

[0054] (iv) Separation characteristics The composite semipermeable membrane according to this embodiment is suitable for separating not only ionic solutes such as sodium chloride, but also nonionic solutes, and is characterized by the difference 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 nonionic neutral silica, and 1 ppm of boron is permeated through the composite semipermeable membrane according to this embodiment at an operating pressure of 0.75 MPa, the silica removal rate is preferably 99.30% or higher, and more preferably 99.45% or higher. Furthermore, the boron removal rate of the composite semipermeable membrane is preferably 60% or higher, more preferably 65% ​​or higher, and even more preferably 70% or higher. In addition, the NaCl removal rate of the composite semipermeable membrane is preferably 99.50% or higher, more preferably 99.60% or higher, while less than 99.90% is preferred. Moreover, the difference between the silica removal rate and the NaCl removal rate is preferably 0.20% or less.

[0056] If the silica removal rate, boron removal rate, NaCl removal rate, and the difference between the silica and NaCl removal rates are within the above range, it is possible to obtain high-quality permeate while simultaneously suppressing solute concentration on the membrane surface, such as scale.

[0057] Furthermore, from the perspective of reducing energy consumption when treating raw water with a composite semipermeable membrane, the permeate volume under the above conditions is 0.70 m³. 3 / m 2 More than one day per day is preferable.

[0058] (1-2) Porous support layer The porous support layer serves as a scaffold for the formation of the separation function layer, but it itself does not substantially possess the ability to separate ions or other substances.

[0059] In terms of the size and distribution of pores in the porous support layer, for example, a porous support layer is preferred that has uniform, fine pores or gradually larger pores 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 polymer onto a substrate, which is a fabric made of at least one of 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. Hereafter, the configuration in which a porous support layer is formed on the substrate may be referred to as a "support membrane".

[0061] As materials for the porous support layer, homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide can be used alone or in blends. As cellulose polymers, cellulose acetate and cellulose nitrate can be used, and as vinyl polymers, polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile can be used. Among these, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, and polyphenylene sulfone are preferred as materials for the porous support layer, and cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone are more preferred. Among these materials, polysulfone is even more preferred because it has high chemical, mechanical, and thermal stability and is easy to mold.

[0062] For example, by dissolving polysulfone in N,N-dimethylformamide (hereinafter referred to as "DMF"), casting a solution to a certain thickness onto a densely woven polyester cloth or polyester nonwoven fabric, and then wet-coagulating it in water, a support film can be obtained in which most of the surface has fine pores with a diameter of several tens of nanometers or less.

[0063] The thickness of the support film mentioned above affects the strength of the resulting composite semipermeable film and the packing density when it is used as an element. From the viewpoint of obtaining sufficient mechanical strength and packing density, the thickness of the support film is preferably 30 μm to 300 μm, and more preferably 100 μm to 220 μm.

[0064] The morphology of the porous support layer can be observed using a scanning electron microscope, transmission electron microscope, or atomic microscope. For example, when observing with a scanning electron microscope, the porous support layer peeled from the substrate is cut using the freeze-fracture method 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 (UHR-FE-SEM) at an accelerating voltage of 3 to 15 kV. UHR-FE-SEMs such as the Hitachi S-900 electron microscope can be used.

[0065] In the composite semipermeable membrane according to this embodiment, the thickness of the porous support layer 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 film without defects can be obtained. A composite semipermeable membrane equipped with such a porous support layer exhibits good salt removal performance. Furthermore, when the thickness of the porous support layer is 100 μm or less, the amount of unreacted substances remaining during manufacturing can be reduced, and a decrease in permeate water volume and chemical resistance can be suppressed.

[0066] (2) Manufacturing method (2-1) Process for forming a porous support layer The process for forming a porous support layer includes the steps of applying a polymer solution to a substrate and immersing the substrate coated with the solution in a solidification bath to solidify the polymer.

[0067] In the process of applying a polymer solution to a substrate, the polymer solution is prepared by dissolving the polymer, which is a component of the porous support layer, in a suitable solvent for that polymer.

[0068] When applying the polymer solution, the temperature of the polymer solution is preferably between 10°C and 60°C, for example, when polysulfone is used as the polymer. When the temperature of the polymer solution is within this range, the polymer does not precipitate, and the polymer solution solidifies after sufficiently impregnating the spaces between the fibers of the substrate. As a result, the porous support layer is firmly bonded to the substrate by the anchoring effect, and a good support film can be obtained. The preferred temperature range of the polymer solution can be appropriately adjusted depending on the type of polymer used and the desired solution viscosity.

[0069] The time between applying the polymer solution to the substrate and immersing it in the solidification bath is preferably 0.1 seconds to 5 seconds. When the time to immerse in the solidification bath is within this range, the organic solvent solution containing the polymer is sufficiently impregnated into the spaces between the fibers of the substrate before solidification. The preferred range for the time to immerse in the solidification bath can be adjusted as appropriate depending on the type of polymer solution used and the desired solution viscosity.

[0070] While water is generally used as the coagulation bath, it is not particularly limited to any bath that does not dissolve the polymer components of the porous support layer. The composition of the coagulation bath affects the morphology of the resulting porous support layer, and consequently, the resulting composite semipermeable membrane also changes. The temperature of the coagulation bath is preferably between -20°C and 100°C, and more preferably between 10°C and 50°C. 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 excessive, and the smoothness of the surface of the porous support layer after its formation is maintained. Furthermore, when the temperature is within the above range, the coagulation rate is appropriate, and film formation is good.

[0071] Next, the obtained support film is washed with hot water to remove any remaining solvent in the film. The temperature of the hot water is preferably between 40°C and 100°C, and more preferably between 60°C and 95°C. When the temperature of the hot water is within the above range, the degree of shrinkage of the support film does not increase, and the amount of permeate is good. In addition, a sufficient cleaning effect can be obtained when the temperature of the hot water is within the above range.

[0072] (2-2) Process for forming the separation functional layer 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 with 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 described above. The process will be explained below using the case in which a polyfunctional aromatic amine is used as the polyfunctional amine and a polyfunctional aromatic acid chloride is used as the polyfunctional acid halide as an example.

[0074] Any organic solvent that is immiscible with water, does not damage the supporting film, and does not inhibit the formation reaction of the crosslinked aromatic polyamide can be used to dissolve the polyfunctional aromatic acid chloride. Typical examples of organic solvents that dissolve polyfunctional aromatic acid chloride include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane. From the viewpoint of not depleting the ozone layer, availability, ease of handling, and safety in handling, elements such as octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, cyclooctane, ethylcyclohexane, 1-octene, and 1-decene, or mixtures thereof, are preferably used.

[0075] In the method for producing a composite semipermeable membrane according to this embodiment, the water content in the organic solvent for dissolving the polyfunctional acid halide is preferably 10 ppm to 50 ppm. By reducing the water content in the organic solvent, inhibition of the polycondensation reaction between the polyfunctional amine and the polyfunctional acid halide by water is suppressed, and an appropriate surface pore size can be formed. Furthermore, if the water content in the organic solvent for dissolving the polyfunctional acid halide is 50 ppm or less, inhibition of the polycondensation reaction is 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 of coarse pores A near the surface layer of the separation functional layer is small and the proportion of coarse pores B on the inner layer side is large, or it makes it easier to produce a separation functional layer in which there are fewer carboxyl groups near the surface layer of the separation functional layer and a low Nd / Nf ratio. For the reasons above, the water content in the organic solvent for dissolving the polyfunctional acid halide is more preferably 10 ppm to 30 ppm.

[0076] The water content in organic solvents can be measured by the Karl Fischer titration method described in JIS K0068:2001. While the Karl Fischer method includes methods such as volumetric titration and coulometric titration, this specification uses the coulometric titration method.

[0077] In the method for producing a composite semipermeable membrane according to this embodiment, the polyfunctional amine aqueous solution includes a polyfunctional amine, a monofunctional amine with 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 with a molecular weight of 150 or less in the interfacial polycondensation allows the monofunctional amine to diffuse into the polyamide network and react with the terminal carboxyl groups of the surface layer, thereby reducing the proportion A of coarse pores near the surface of the separation functional layer, or reducing the number of carboxyl groups near the surface 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 a monofunctional amine with a molecular weight of 150 or less in the polyfunctional amine aqueous solution is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.05% by mass or more and 8% by mass or less. When the concentration of the monofunctional amine is within the above range, the removal of neutral molecules can be improved without impairing the salt removal performance of the separation functional layer.

[0079] Furthermore, the presence of an aqueous layer additive having an amide group or a urea group in the polyfunctional amine aqueous solution promotes the hydrolysis reaction between 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 of the separation functional layer, or increasing the carboxyl group density in the inner layer compared to the surface layer.

[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 containing 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 polyfunctional amine aqueous 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 polyfunctional amine aqueous solution is within the above range, it is possible to form a separation functional layer 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, first, the surface of the porous support layer is coated with an aqueous solution of polyfunctional aromatic amine. The concentration of the polyfunctional aromatic amine in the aqueous 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.

[0084] Methods for coating the surface of a porous support layer with a polyfunctional aromatic amine aqueous solution include ensuring that the surface of the porous support layer is uniformly and continuously coated with the aqueous solution, and include 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.

[0085] The contact time between the porous support layer and the polyfunctional aromatic amine aqueous solution is preferably 5 seconds to 10 minutes, and more preferably 10 seconds to 3 minutes. Next, it is preferable to remove any excess aqueous solution by a de-liquidation step. Examples of de-liquidation methods include holding the support film surface vertically and allowing it to flow naturally. After de-liquidation, the support film surface may be dried to remove all or part of the water in the aqueous solution.

[0086] Subsequently, the porous support layer coated with an aqueous solution of polyfunctional aromatic amine is coated with the above-mentioned polyfunctional aromatic acid chloride solution, and a crosslinked aromatic polyamide is formed by interfacial polycondensation. The time for performing interfacial polycondensation is preferably 0.1 seconds to 3 minutes, and more preferably 0.1 seconds to 1 minute.

[0087] The concentration of 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 sufficiently forming a separation functional layer and from the viewpoint of cost.

[0088] Next, any organic solvent remaining after the reaction is preferably removed by a dewatering step. For example, the organic solvent can be removed by grasping the composite semipermeable membrane vertically and allowing the excess organic solvent to flow down naturally. In this case, the grasping time in the vertical direction is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. If the grasping time is 1 minute or more, it is easier to obtain a crosslinked aromatic polyamide with the desired function, and if it is 5 minutes or less, the occurrence of defects due to over-drying of the organic solvent can be suppressed, thereby suppressing performance degradation.

[0089] (3) Use of composite semipermeable membranes The composite semipermeable membrane according to this embodiment is preferably used as a spiral-type composite semipermeable membrane element, wound around a cylindrical water collection pipe with numerous holes, together with a raw water channel material such as a plastic net, a permeable water channel material such as tricot, and a film to enhance pressure resistance as needed. Furthermore, a composite semipermeable membrane module can be formed by connecting these elements in series or parallel and housing them in a pressure vessel.

[0090] Furthermore, the composite semipermeable membranes, their elements, and modules can be combined with pumps that supply raw water to them, and equipment that pre-treats the raw water, to constitute a fluid separation system. By using this separation system, raw water can be separated into permeate (such as drinking water) and concentrated water that did not permeate the membrane, thereby obtaining water suitable for the purpose.

[0091] The temperature of the raw water supplied to the fluid separation device is preferably between 5°C and 45°C, from the viewpoint of achieving good salt removal efficiency and membrane permeation flux. Furthermore, it is preferable to operate the device with the pH of the raw water in the neutral range in order to suppress scale formation such as magnesium and to suppress membrane deterioration.

[0092] The module using the composite semipermeable membrane of this embodiment is characterized by its high ability to remove neutral molecules. For example, it can be particularly suitable for introduction into processes when producing ultrapure water from raw water containing trace amounts of organic matter or silicates, such as in ultrapure water production processes used in semiconductor manufacturing.

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

[0094] In this embodiment, the only essential step in the ultrapure water production method is the reverse osmosis process; the other steps are optional. The following describes each of these steps.

[0095] (3-2) Pretreatment process (3-2-1) Raw water The raw water targeted in this embodiment is an aqueous solution containing silica (hereinafter referred to as "silica-containing aqueous solution" regardless of whether the pretreatment process has been carried out), and specifically, examples include river water, groundwater, wastewater recovery water, and cooling water blowdown water. Silica often exists as silicates, and its charged state changes depending on the pH of the raw water, but it is less likely to be charged in the neutral range (pH 6 to 8). Boric acid also changes its charged state depending on the pH of the raw water, but it is less likely to be charged in the neutral range (pH 6 to 8).

[0096] (3-2-2) Pretreatment method The ultrapure water production method of this embodiment preferably includes a pretreatment step to remove suspended solids from the raw water before the primary treatment step (reverse osmosis step) described later. Suspended solids contained in the raw water can cause clogging (fouling) if they adhere to the surface of the reverse osmosis membrane used in the subsequent primary treatment step. Therefore, fouling can be suppressed by filtering (pretreatment) part or all of the raw water by passing it through an MF membrane (microfiltration membrane) or UF membrane (ultrafiltration membrane) before supplying it to the primary treatment step.

[0097] (3-3) Primary treatment process (reverse osmosis process) (3-3-1) Reverse osmosis membrane (RO membrane) The ultrapure water production method of this embodiment includes a reverse osmosis step to remove silica 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 by using the composite semipermeable membrane of this embodiment as a reverse osmosis membrane in a primary treatment step. Due to the high permeability of the reverse osmosis membrane, the amount of concentrated water (waste water) can be reduced as a high recovery rate operation without increasing the operating pressure, and a highly efficient process can be realized. In addition, the high silica removal rate of the reverse osmosis membrane can reduce the silica concentration of the aqueous solution supplied from the primary treatment step to the secondary treatment step described later. Therefore, the deposition of silica on the surface of the ion exchange resin used in the secondary treatment step, and the resulting decrease in the processing efficiency of the secondary treatment step and deterioration of the ion exchange resin can be suppressed.

[0098] (3-3-2) Driving Method In reverse osmosis filtration, it is preferable to supply raw water or a pre-treated 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 suppress a decrease in the membrane permeation rate of water, and a pressure of 12 MPa or lower can reduce the possibility of affecting membrane damage. From the above viewpoint, the pressure at which raw water or a pre-treated aqueous solution is supplied is more preferably 0.25 MPa to 6 MPa, and even more preferably 0.25 MPa to 1 MPa. The permeate volume of the reverse osmosis membrane is 0.85 m³. 3 / m 2If the permeation rate is 1 MPa or more, it becomes possible to obtain a sufficient amount of permeate even with low-pressure operation of 1 MPa or less, which reduces energy consumption per unit of water produced and the cost of water production. In addition, it becomes possible to design equipment using small-scale pumps, resulting in space savings.

[0099] The primary treatment step may be a multi-stage process; that is, the aqueous solution after pretreatment 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 wastewater and increase the recovery rate, the concentrated water obtained by filtering through the first reverse osmosis membrane may be treated through the second reverse osmosis membrane.

[0100] (3-4) Secondary processing steps The ultrapure water production method of this embodiment preferably further includes a step of removing solute salts from the aqueous solution treated in the reverse osmosis step using an ion exchange resin. That is, it is preferable to include a secondary treatment step of further removing ionic components from the permeate obtained in the primary treatment step to obtain ultrapure water. It is preferable to use an ion exchange resin (hereinafter also referred to as "ion exchanger") in the secondary treatment step.

[0101] Methods using ion exchange resins may include using an ion exchange apparatus containing cation exchange resins and anion exchange resins, or using electro-regenerative deionization (hereinafter referred to as "EDI"). EDI is a device having a desalination chamber partitioned by an ion exchange membrane and filled with an ion exchange material, a concentration chamber for concentrating the ions desalined in the desalination chamber, and an anode and cathode for conducting electric current. By operating the device with electric current, it simultaneously performs desalination (deionization) of the water to be treated by the ion exchange material and regeneration of the ion exchange material. The water to be treated passed through the EDI is desalinized by the ion exchange material filled in the desalination chamber and 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 processing step may include UV treatment. [Examples]

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

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

[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 for membrane filtration. The membrane area of ​​the composite semipermeable membrane was 33 cm². 2 Two hours after starting the membrane filtration process, the permeate was sampled for 20 minutes. The electrical conductivity of the raw 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., the NaCl concentration, for each. The NaCl removal rate was calculated from the obtained NaCl concentrations based on the following formula. Here, the NaCl concentration (ppm) refers to the concentration on a mass basis. NaCl removal rate (%) = 100 × {1 - (NaCl concentration in permeate / NaCl concentration in raw water)}

[0106] Furthermore, the silica and boron concentrations in the raw water and permeate were measured using an ICP emission spectrometer (Agilent 5110VDV), and the silica and boron removal rates were calculated using the following formulas. Silica removal rate (%) = 100 × {1 - (Silica concentration in permeate water / Silica concentration in raw water)} Boron removal rate (%) = 100 × {1 - (boron concentration in permeate water / boron concentration in raw water)}

[0107] <Permeated water amount> In the "solute removal rate" test described above, the amount of raw water permeated through the membrane was measured, and the value converted to the daily permeability (cubic meters) per square meter of membrane surface was used as the permeability (m³). 3 / m 2 ( / day)

[0108] <Percentage of coarse pores> A 5cm square composite semipermeable membrane, from which the substrate had been physically detached, was processed by the freeze-ultrathin sectioning method, placed on a copper grid, immersed in pure water for 4 hours, and then immersed in a 10% by mass 2-propanol aqueous solution for 1 hour for washing. After that, the moisture from the sample was removed with filter paper and freeze-dried to obtain the measurement sample. The prepared measurement sample was imaged using a field emission transmission electron microscope (Hitachi High-Tech HF5000) under an acceleration voltage of 200kV, and a STEM image at 100,000x magnification was obtained. Subsequently, the obtained image was analyzed with image processing software, and as shown in Figure 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 containing 50-100% of the height of each convex part of the fold structure of the separation functional layer. With the normal V0 passing through the reference point P as the center, straight lines V1 and V2 parallel to the normal V0 were drawn on both sides at intervals of 3-10nm. Furthermore, a tangent line Z1 on the outer surface of the separator layer passing through reference point P and a tangent line Z2 on the inner surface 25 of the separation function layer (the surface in contact with the porous support layer) parallel to Z1 were drawn. Between Z1 and Z2, a straight line Z3 was drawn that bisects the distance between Z1 and Z2. The regions enclosed by V1 and V2, and also enclosed by Z1, Z2 and the straight line Z3 between them, were designated as region a and region b, respectively, starting from the outer surface side of the separation function layer. The area of ​​region a and region b is 10 nm. 2 Above 80nm 2 The following was performed. Furthermore, STEM images were deconvolved using DeConvHAADF (HREM research inc.) to highlight the pores and polyamide structure. Next, binarization was performed using ImageJ, and particle size analysis was conducted 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. Using the calculated pore diameter and pore area, the proportions of coarse pores with a diameter of 0.7 nm or more in regions a and b, respectively, were calculated using the following formulas. Note that the average proportion of coarse pores obtained for the five protrusions of the separation functional layer was used as the proportion of coarse pores in each region. The ratio of coarse pores A = the proportion of coarse pores in region a AreaSum of pixels / all holes in area a Area Total number of pixels The ratio of coarse pores B = the proportion of coarse pores in region b Area Total number of pixels / all holes in area b Area Total number of pixels

[0109] <Carboxyle group density> A 5cm square composite semipermeable membrane, from which the substrate had been physically detached, was treated by the freeze-ultrathin sectioning method, placed on a copper grid, immersed in pure water for 4 hours, and then immersed in a 10% by mass 2-propanol aqueous solution for 1 hour for washing. Subsequently, 1.0 × 10⁻⁶ solutions were prepared in a solution adjusted to pH 3.8 and 25°C. -3 The sample was immersed in a mol / L barium chloride aqueous solution for 10 minutes a total of three times, followed by a 1.0 × 10⁶ solution with pH adjusted to 3.8 and temperature at 25°C. -7 The sample was immersed in a mol / L barium chloride aqueous solution for 7 minutes a total of four times. After that, the moisture was removed from the sample using filter paper, and it was freeze-dried to prepare the measurement sample. The prepared measurement sample was imaged using a field emission transmission electron microscope (Hitachi High-Tech HF5000) under an acceleration voltage of 200kV, and a STEM image at 100,000x magnification was obtained. Then, as shown in Figure 6, 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 containing 50-100% of the height of each convex part of the fold structure of the separation functional layer. With the normal vector V0 passing through reference point P as the center, straight lines V1 and V2 parallel to the normal vector V0 were drawn on both sides at intervals of 3-10 nm. In addition, a tangent Z1 on the outer surface of the separation functional layer passing through reference point P and a tangent Z2 on the inner surface 25 of the separation functional layer (the surface in contact with the porous support layer) parallel to it were drawn. Four straight lines were drawn between Z1 and Z2, dividing the gap into five equal parts. The region enclosed by V1 and V2, and also enclosed by Z1, Z2 and the lines between them, was designated as regions c to g, starting from the first surface side of the composite semipermeable film. The area of ​​each region c to g is 5 nm. 2 More than 30nm 2The following was done. The obtained images were analyzed using image processing software, and the brightness was measured by STEM in the regions c to g described above. For the minimum brightness Lmin and maximum brightness Lmax of these measurements, the area of ​​regions showing a brightness of {Lmin + (Lmax - Lmin) / 3} or greater was integrated for each region. This integral value represents the total area of ​​the parts containing carboxyl groups labeled with barium (Ba). The obtained integral value was used to determine the area per carboxyl group molecule (0.04 nm). 2 ), Avogadro's number (6.0 × 10⁻¹⁰ 23 By dividing by the number of molecules / mol and the area of ​​each region, the carboxyl group density (mol / nm) can be calculated. 2 The following was calculated. The average value of the carboxyl group density measured for five randomly selected protrusions in the separation functional layer was used as the carboxyl group density for each region.

[0110] <Terminal amino group C, terminal carboxyl group D, amide group E> Composite semipermeable membrane 5m 2 The substrate was physically peeled off, and the porous support layer and separation functional layer were recovered. After drying by standing at 25°C for 24 hours, the layers were added in small amounts to a beaker containing dichloromethane and stirred to dissolve the polymer constituting the porous support layer, and the insoluble matter in the beaker was collected with filter paper. This insoluble matter was added to the beaker containing dichloromethane and stirred, and the insoluble matter in the beaker was collected. This process was repeated until no more polymers forming the porous support layer were detected eluting into the dichloromethane solution. The recovered separation functional layer was dried in a vacuum dryer to remove any remaining dichloromethane. The obtained separation functional layer was obtained as a powder sample by freeze-grinding, sealed in a sample tube used for solid-state NMR measurement, and subjected to CP / MAS and DD / MAS methods. 13 Solid-state NMR measurements were performed. 13 For 13C solid-state NMR measurements, a Chemagnetics CMX-300 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: 100s From the obtained spectrum, peak splitting was performed for each peak originating from the carbon atom to which each functional group is bonded, and the functional group ratio was quantified from the area of ​​the split peaks.

[0111] <Contact angle> Using a Drop Master DM500 manufactured by Kyowa Interface Science Co., Ltd., the static contact angle was automatically calculated by computer image analysis using the θ / 2 method. 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 (air permeability 2.0 cc / cm²) 2 A support film with a porous support layer thickness of 40 μm was prepared by casting a 15.0% by mass DMF solution of polysulfone onto the surface at 25°C and immediately immersing it in pure water for 5 minutes. Next, this support film was immersed in a polyfunctional amine aqueous solution containing 2.0% by mass of m-PDA as a polyfunctional amine, 0.1% by mass of ethylamine as a monofunctional amine with a molecular weight of 150 or less, and 1.2% by mass of DMF as an aqueous layer additive, and then the excess aqueous solution was removed. Furthermore, a polyfunctional acid halide solution prepared using n-decane with a water content of 40 ppm as an organic solvent so that the TMC concentration as a polyfunctional acid halide was 0.10% by mass was added to the surface of the porous support layer at a concentration of 300 mL / m². 2 The film was coated, and a separation functional layer was formed by interfacial polycondensation. Next, to remove excess solution from the film, the film was held vertically and drained, then dried by blowing 25°C air using a blower, and finally washed with 80°C pure water to obtain the composite semipermeable film of Example 1.

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

[0114] [Example 3] The composite semipermeable membrane of Example 3 was obtained by the same method as in Example 1, except that N,N'-dimethylpropylene urea (hereinafter referred to as "DMPU") was used as the aqueous layer additive.

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

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

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

[0118] [Example 7] The composite semipermeable membrane of Example 7 was obtained by the same method 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] The composite semipermeable membrane of Example 8 was obtained by the same method as in Example 7, except that the moisture content of n-decane was set to 80 ppm.

[0120] [Example 9] The composite semipermeable film of Example 9 was obtained by the same method 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 by the same method as in Example 1, except that ethylamine and DMF were not added to the polyfunctional amine aqueous solution.

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

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

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

[0125] [Comparative Example 5] A composite semipermeable membrane of Comparative Example 5 was obtained by the same method 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 film of Comparative Example 6 was obtained by the same method as in Example 1, except that 0.10% by mass of DMF was added to a polyfunctional acid halide solution as an organic layer additive, instead of adding DMF to the polyfunctional amine aqueous solution.

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

[0128] The structure and performance of the composite semipermeable membranes obtained in Examples 1-9 and Comparative Examples 1-7 are shown in Table 1.

[0129] [Table 1]

[0130] Thus, 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, demonstrate that they achieve both high permeability and removal of neutral molecules.

[0131] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the present invention.

[0132] This application is based on Japanese patent applications filed on March 26, 2024 (JP 2024-049332) and Japanese patent applications filed on March 26, 2024 (JP 2024-049342), which are incorporated herein by reference in their entirety. [Explanation of Symbols]

[0133] 1 Composite semipermeable membrane 2 Base material 3 Porous support layer 4 Separation functional layer 11. The first surface of a composite semipermeable membrane. 12. Second surface of a composite semipermeable membrane 21 Convex part i 22 Convex part ii 23 Height of protrusion i 24 Height of protrusion ii 25 Inner surface of the separation functional layer 26 Outer surface of the separation functional layer 27 Pleat thickness X Roughness curve average line Elevation of the 5th highest peak from Yp1~5 X Yv1~5 Elevation of the valley floors from the lowest valley floor to the 5th valley floor from X L (standard length) P reference point V0 is the normal vector passing through reference point P. V1 and V2 are straight lines parallel to the normal vector V0. Z1 is the tangent to the outer surface of the separation functional layer passing through reference point P. Tangent to the inner surface of the separation functional layer parallel to tangent Z1 A straight line that bisects 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, The surface of the composite semipermeable membrane has a first surface which is the surface in the direction on which the separation functional layer exists relative to the porous support layer, and a second surface which is the surface on the opposite side of the first surface. The separation functional layer contains a crosslinked polyamide, A composite semipermeable membrane in which the cross-section in the thickness direction of the separation functional layer, observed by a scanning transmission electron microscope, is divided into two equal parts, region a on the first surface side and 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 denoted as A, and the proportion of coarse pores with a pore diameter of 0.7 nm or more in region b is denoted as B, A / B is 1.35 or less.

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

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

4. The composite semipermeable membrane according to claim 1 or 2, 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.

5. A composite semipermeable membrane element comprising a composite semipermeable membrane according to claim 1 or 2.

6. A composite semipermeable membrane module comprising the composite semipermeable membrane element described in claim 5.

7. A method for producing a composite semipermeable membrane according to Claim 1, The composite semipermeable membrane comprises a substrate and a support membrane having the porous support layer, and the separation functional layer provided on the porous support layer. 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 the porous support layer. The aforementioned polyfunctional amine aqueous solution comprises a polyfunctional amine, a monofunctional amine with a molecular weight of 150 or less, and an aqueous layer additive having an amide group or a urea group. The method for producing a composite semipermeable membrane comprises a polyfunctional acid halide solution and an organic solvent.

8. The method for producing a composite semipermeable membrane according to claim 7, wherein the molecular weight of the monofunctional amine is 100 or less.

9. A method for producing a composite semipermeable membrane according to claim 7 or 8, wherein the water content in the organic solvent is 10 ppm or more and 50 ppm or less.

10. A method for producing a composite semipermeable membrane according to claim 7 or 8, wherein the concentration of the monofunctional amine in the polyfunctional amine aqueous solution is 0.01% by mass or more and 10% by mass or less.

11. The method for producing a composite semipermeable membrane according to claim 7 or 8, wherein the concentration of the aqueous layer additive in the polyfunctional amine aqueous solution is 0.01% by mass or more and 10% by mass or less.

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

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