Composite semipermeable membrane

Abstract

To provide a composite semipermeable membrane that exhibits both separation performance and water permeability while exhibiting excellent chlorine resistance.SOLUTION: The composite semipermeable membrane comprises a microporous support layer and a separation function layer disposed on the microporous support layer, where the separation function layer contains a polyamide which has a partial structure represented by the general formula (1) described in the specification.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] The membrane separation method is expanding as a method for removing substances (such as salts) dissolved in a solvent (such as water) from the solvent. The membrane separation method is attracting attention as an energy-saving and resource-saving method.

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

[0004] Most of the currently commercially available reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes. Examples of the composite semipermeable membranes include those having an active layer in which a gel layer and a polymer are crosslinked on a porous support layer, and those having a porous support layer and an active layer formed by polycondensation of a monomer on the porous support layer. Among the latter composite semipermeable membranes, a composite semipermeable membrane having a separation functional layer containing a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide is widely used as a separation membrane having high permeability and selective separability.

[0005] Here, in various water treatments such as desalination plants, although the chlorine added in the pretreatment is designed in principle not to come into contact with the membrane during operation, there is a risk that the leaked chlorine due to an operation error comes into contact with the membrane and the membrane is oxidatively deteriorated. Therefore, in order to reduce the risk of membrane deterioration due to chlorine leakage and extend the membrane life, studies have been conducted on improving the chlorine resistance of these composite semipermeable membranes.

[0006] As methods for improving chlorine resistance, a method of improving monomer components for forming a separation functional layer and a method of forming a protective layer on the separation functional layer are known. Patent Document 1 discloses using sodium m-phenylenediamine-4-sulfonate as a polyfunctional amine for forming a separation functional layer, and Patent Document 2 discloses using a compound having hexafluoroalcohol as a side chain as a polyfunctional amine for forming a separation functional layer.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] Among the various proposals described above, there are membranes having chlorine resistance, but there are limitations in achieving both water permeability and removability. An object of the present invention is to provide a composite semipermeable membrane having water permeability and removability that can withstand practical use and having high removability even after contact with chlorine.

Means for Solving the Problems

[0009] To achieve the above object, the composite semipermeable membrane of the present invention has any of the following configurations. [1] A composite semipermeable membrane having a microporous support layer and a separation functional layer provided on the microporous support layer, wherein the separation functional layer contains polyamide, and the polyamide has a partial structure represented by (1), Composite semipermeable membrane.

[0010]

Chemical Formula

[0011] [2] The composite semipermeable membrane according to [1], wherein the polyamide is a crosslinked aromatic polyamide. [3] The composite semipermeable membrane according to [2], wherein the crosslinked aromatic polyamide has a partial structure represented by (2).

[0012] [Chemical formula]

[0013] (R1 to R4 are hydrogen atoms or aliphatic chains having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L1 is a single bond or an aliphatic chain or aromatic ring having 1 to 8 atoms which may contain heteroatoms, and X is any atomic group which may contain a crosslinked structure.) [4] The composite semipermeable membrane according to [2] or [3], wherein the crosslinked aromatic polyamide has a partial structure represented by (3).

[0014] [Chemical formula]

[0015] (R1 to R4 are hydrogen atoms or aliphatic chains having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L2 is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain heteroatoms, and X is any atomic group which may contain a crosslinked structure.) [5] The composite semipermeable membrane according to [3] or [4], wherein X in the above structure is represented by (4).

[0016] [Chemical formula]

[0017] (R1 to R4 are hydrogen atoms or aliphatic chains having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L3 is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain hetero atoms, and Y is an arbitrary atomic group.) [6] The composite semipermeable membrane according to any one of [4] or [5], wherein L2 of the structure (3) and L3 of (4) are a single bond or an aliphatic chain having 1 to 6 carbon atoms which may contain hetero atoms. [7] The composite semipermeable membrane according to any one of [4] to [6], wherein L2 of the structure (3) and L3 of (4) are single bonds. [8] The composite semipermeable membrane according to any one of [1] to [7], wherein the zeta potential at pH 3 is 0 mV or less in the composite semipermeable membrane. [9] For the separation functional layer extracted from the composite semipermeable membrane, the following value x satisfies x ≦ 0.80, The composite semipermeable membrane according to any one of claims 1 to 8.

[0018] x = z / y y: Mass at a relative humidity of 95% and a temperature of 25 °C z: Mass at a relative humidity of 0% and a temperature of 25 °C [Advantages of the Invention]

[0019] According to the present invention, it is possible to provide a composite semipermeable membrane having excellent separation performance and water permeation performance, and further showing high salt removal performance even after contact with chlorine. [Brief Description of the Drawings]

[0020]

Figure 1

[0021] 1. Composite semipermeable membrane The composite semipermeable membrane according to an embodiment of the present invention is a composite semipermeable membrane having a microporous support layer and a separation functional layer provided on the microporous support layer.

[0022] As one embodiment of the present invention, as shown in Fig. 1(a), the composite semipermeable membrane 1 has a microporous support layer 3 and a separation functional layer 4 provided on the microporous support layer 3. The microporous support layer 3 may be formed on a substrate 2.

[0023] (1-1) Support membrane In the form shown in Fig. 1(a), the composite semipermeable membrane 1 includes a substrate 2 and a microporous support layer 3. However, the support membrane may have no substrate and may be composed only of a microporous support layer. That is, the microporous support layer may be a support membrane.

[0024] (1-2) Substrate Examples of the substrate include polyester-based polymers, polyamide-based polymers, polyolefin-based polymers, or mixtures or copolymers thereof. Among them, a fabric of a polyester-based polymer having high mechanical and thermal stability is particularly preferable.

[0025] (1-3) Microporous support layer The microporous support layer has substantially no separation performance for ions or the like, and is for imparting strength to a separation functional layer having substantial separation performance. The size and distribution of the pores of the microporous support layer are not particularly limited. For example, a microporous support layer having uniform and fine pores, or gradually larger fine pores from the surface on the side where the separation functional layer is formed to the other side, and having a fine pore size of 0.1 nm or more and 100 nm or less on the surface where the separation functional layer is formed is preferable, but the material used and its shape are not particularly limited.

[0026] Examples of materials for the microporous support layer include homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide, which can be used alone or in blends. Here, examples of cellulose polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile. Among them, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferred. More preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone can be mentioned. Among these materials, polysulfone is generally used because it has high chemical, mechanical, and thermal stability and is easy to mold.

[0027] When measuring polysulfone by gel permeation chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard substance, the mass average molecular weight (Mw) is preferably 10,000 or more and 200,000 or less, more preferably 15,000 or more and 100,000 or less. When Mw is 10,000 or more, preferable mechanical strength and heat resistance as a microporous support layer can be obtained. Also, when Mw is 200,000 or less, the viscosity of the solution is within an appropriate range, and good moldability can be realized.

[0028] The thicknesses of the base material and the microporous support layer affect the strength of the composite semipermeable membrane and the packing density when it is used as an element. In order to obtain sufficient mechanical strength and packing density, the total thickness of the base material and the microporous support layer is preferably 30 μm or more and 300 μm or less, and more preferably 100 μm or more and 220 μm or less. Further, the thickness of the microporous support layer is preferably 20 μm or more and 100 μm or less. In this document, unless otherwise specified, the thickness means the average value. Here, the average value represents the arithmetic mean value. That is, the thicknesses of the base material and the microporous support layer are determined by calculating the average value of the thicknesses of 20 points measured at 20-μm intervals in the direction perpendicular to the thickness direction (the plane direction of the membrane) by cross-sectional observation.

[0029] (1-4) Separation functional layer In the embodiment of the present invention, the separation functional layer contains polyamide. In particular, the separation functional layer preferably contains crosslinked aromatic polyamide as a main component. The main component refers to a component that occupies 50% by mass or more of the components of the separation functional layer. The separation functional layer can exhibit high removal performance by containing 50% by mass or more of crosslinked aromatic polyamide. Further, the separation functional layer is preferably formed substantially only of crosslinked aromatic polyamide. That is, it is preferable that crosslinked aromatic polyamide occupies 90% by mass or more of the separation functional layer.

[0030] The separation functional layer according to the embodiment of the present invention contains polyamide, and the polyamide has a partial structure represented by the following general formula (1).

[0031]

Chemical formula

[0032] The partial structure represented by the general formula (1) is preferably a structure in which the terminal amino group of the polyamide is substituted. That is, when the polyamide is crosslinked aromatic polyamide, it preferably has a partial structure represented by the following general formula (2).

[0033]

Chemical formula

[0034] (R1 to R4 are a hydrogen atom or an aliphatic chain having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L1 is a single bond or an aliphatic chain or aromatic ring having 1 to 8 atoms which may contain a hetero atom, and X is an arbitrary atomic group which may contain a cross-linked structure.) Such a structure of the polyamide has a lower energy level compared to the terminal amino group, so the oxidation resistance is improved and the structure is less likely to change even after chlorine contact. In addition, since it has a thioether bond which is a hydrophilic group, the water permeability of the composite semipermeable membrane becomes practical.

[0035] Also, L1 in (2) preferably contains an amide bond. That is, it is preferable that the polyamide has a partial structure represented by the following general formula (3).

[0036]

Chemical formula

[0037] (R1 to R4 are a hydrogen atom or an aliphatic chain having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L2 is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain a hetero atom, and X is an arbitrary atomic group which may contain a cross-linked structure.) By substituting the terminal amino group with an amide bond as in (3), hydrophilicity is imparted to the polyamide, and the water permeability is improved compared to the case where L1 in (2) does not contain an amide bond.

[0038] Furthermore, it is more preferable to have a structure in which a plurality of terminal amino groups are cross-linked. That is, it is more preferable that X in the general formula (2) or (3) has a structure represented by the following general formula (4).

[0039]

Chemical formula

[0040] (R1 to R4 are hydrogen atoms or aliphatic chains having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L3 is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain hetero atoms, and Y is any atomic group.) Thus, a structure in which terminal amino groups are crosslinked by a plurality of thioether bonds is more preferable because it has strong chlorine resistance, not only has practical water permeability, but also exhibits a high salt rejection rate.

[0041] L1 in the general formula (2) or L2 in (3), and L3 in (4) may have the same structure or may be different from each other, and are more preferably a single bond or an aliphatic chain having 1 to 6 carbon atoms which may contain hetero atoms. When it is a single bond or an aliphatic chain having 1 to 6 carbon atoms, the efficiency of the amino group conversion reaction described later is improved due to the flexibility of the structure, and a membrane having more excellent chlorine resistance can be obtained. Most preferably, L2 and L3 are single bonds.

[0042] The zeta potential of the separation functional layer at pH 3 is preferably 0 mV or less, and more preferably -5 mV or less. The zeta potential is a measure of the net fixed charge on the surface of a flat sample. The crosslinked aromatic polyamide contained in the separation functional layer mainly has amino groups and carboxyl groups as terminal functional groups, and the degree of dissociation of these depends on pH. At pH 3, the amino groups are mainly positively charged and the carboxyl groups are mainly neutral. That is, it is considered that the zeta potential of the separation functional layer at pH 3 mainly depends on the amount of amino groups. When the zeta potential of the separation functional layer at pH 3 is 0 mV or less, the amount of amino groups that serve as the starting point of degradation by chlorine is small, so a composite semipermeable membrane having excellent chlorine resistance can be obtained.

[0043] The separation functional layer constituting the composite semipermeable membrane preferably has a high water content. When the separation functional layer has a high water content, many paths that selectively permeate only water are formed in the separation functional layer, and a composite semipermeable membrane with excellent water permeation performance can be obtained while maintaining excellent separation performance. As a result of intensive studies by the inventors, it has been found that when the water content rate of the separation functional layer is 0.20 or more, good water permeation performance is exhibited. Here, the water content rate is a value defined as the ratio of the mass at the time when the change in mass due to water content has disappeared when the separation functional layer extracted from the composite semipermeable membrane is left standing in an environment of 95% relative humidity and 25°C to the mass of the separation functional layer from which water has been completely removed.

[0044] In known composite semipermeable membranes, membranes rich in removability generally have a high polyamide density and tend to have a low water content rate. As a result, membranes rich in removability tend to be insufficient in forming selective permeation paths for water in the separation functional layer and tend to be inferior in water permeability. The membrane of the present invention is characterized in that, after forming a selective permeation path for water, the terminal functional group is converted, so that it exhibits high removal performance while ensuring water permeability.

[0045] As shown in FIG. 1(b), the separation functional layer 4 preferably includes a corrugated thin film 41 having a plurality of convex portions 42 and concave portions 43. By having a corrugated thin film as the separation functional layer, the specific surface area of the separation functional layer can be significantly improved as compared with a planar structure. As a result, while maintaining the separation performance, the permeation performance can be improved in proportion to the surface area of the separation functional layer. As shown in FIG. 1(c), the inside of the convex portion 42 (between the thin film 41 and the microporous support layer 3) is a void.

[0046] Further, the average value of the thickness T of the thin film is preferably 10 to 20 nm, and more preferably 10 to 16 nm. By the average value of the thickness T of the thin film being within the above range, a composite semipermeable membrane that achieves both separation performance and water permeation performance can be obtained.

[0047] In order to prevent the substance to be separated from penetrating into the composite semipermeable membrane, the separation functional layer is preferably disposed on the surface side of the composite semipermeable membrane, and more preferably disposed on the primary filtration side. The primary filtration side refers to the membrane surface in contact with the liquid on the raw filtrate side among the liquids separated by the composite semipermeable membrane in the filtration operation.

[0048] Polyamide can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. In particular, crosslinked aromatic polyamide can be formed by interfacial polycondensation of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide. Here, it is preferable that at least one kind of monomer classified into at least one of the amine and the acid halide contains a compound having three or more functional groups.

[0049] The separation functional layer in the present invention may hereinafter be referred to as a polyamide separation functional layer.

[0050] A polyfunctional amine means an amine having two or more amino groups of at least one of a primary amino group and a secondary amino group in one molecule. For example, as polyfunctional amines, polyfunctional aliphatic amines having two amino groups such as piperazine, 2,5-dimethylpiperazine, 2,5-diethylpiperazine, 1,2-cyclohexanediamine, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, etc., polyfunctional aromatic amines in which two amino groups are bonded to an aromatic ring in any positional relationship of ortho, meta, or para positions such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, p-diaminopyridine, etc., polyfunctional aromatic amines such as 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3-aminobenzylamine, 4-aminobenzylamine, etc. can be mentioned. In particular, considering the selective separability, permeability, and heat resistance of the membrane, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used as polyfunctional amines. Among them, it is more preferable to use m-phenylenediamine (hereinafter also referred to as m-PDA) because of its easy availability and easy handling.

[0051] A polyfunctional acid halide means an acid halide having at least two carbonyl halide groups in one molecule. For example, as trifunctional acid halides, trimesic acid chloride, cyclohexane-1,3,5-tricarbonyl chloride, etc. can be mentioned, and as bifunctional acid halides, biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalenedicarboxylic acid chloride, cyclohexane-1,2-dicarbonyl chloride, cyclohexane-1,3-dicarbonyl chloride, cyclohexane-1,4-dicarbonyl chloride, etc. can be mentioned. Considering the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional aromatic acid chloride, and considering the selective separability and heat resistance of the composite semipermeable membrane, it is preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule.

[0052] 2. Method for manufacturing composite semipermeable membrane Next, the method for manufacturing the composite semipermeable membrane will be described. The composite semipermeable membrane includes a step of forming a microporous support layer on a substrate and a step of forming a separation functional layer on the microporous support layer.

[0053] (2-1) Formation of microporous support layer As the substrate and the microporous support layer, an appropriate membrane can be selected from various commercially available membranes such as "Millipore Filter VSWP" (trade name) manufactured by Millipore Corporation and "Ultrafilter UK10" (trade name) manufactured by Toyo Roshi Kaisha, Ltd.

[0054] Also, it can be manufactured according to the method described in "Office of Saline Water Research and Development Progress Report" No. 359 (1968). In addition, a known method as a method for forming the microporous support layer is preferably used.

[0055] (2-2) Method for manufacturing separation functional layer Next, the formation step of the separation functional layer constituting the composite semipermeable membrane will be described.

[0056] The formation step of the separation functional layer is (a) A step of bringing an aqueous solution containing a polyfunctional amine into contact with the microporous support layer; (b) A step of bringing an organic solvent solution containing a polyfunctional acid halide into contact with the microporous support layer contacted with the aqueous solution containing a polyfunctional amine; (c) A step of heating the microporous support layer contacted with the organic solvent solution containing a polyfunctional acid halide; (d) A step of washing the composite semipermeable membrane from which the organic solvent solution has been drained; (e) A step of treating the washed composite semipermeable membrane with a chemical dissolved in an appropriate solvent to impart the partial structure represented by (1), (2), (3) or (4) to the polyamide preferably has.

[0057] Examples of the microporous support layer, polyfunctional amine, and polyfunctional acid halide include those described above, and preferred examples are the same.

[0058] In step (a), the concentration of the polyfunctional amine in the aqueous polyfunctional amine solution is preferably in the range of 0.1% by mass or more and 20% by mass or less, more preferably in the range of 0.5% by mass or more and 15% by mass or less. When the concentration of the polyfunctional amine is within this range, sufficient solute removal performance and water permeability can be obtained.

[0059] The aqueous polyfunctional amine solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, etc., as long as they do not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effect of improving the wettability of the surface of the support membrane and reducing the interfacial tension between the aqueous polyfunctional amine solution and the nonpolar solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and in some cases, the interfacial polycondensation reaction can be carried out efficiently by adding it.

[0060] The contact of the aqueous polyfunctional amine solution is preferably carried out uniformly and continuously on the microporous support layer. Specifically, for example, a method of coating the microporous support layer with the aqueous polyfunctional amine solution or a method of immersing the microporous support layer in the aqueous polyfunctional amine solution can be mentioned. The contact time between the microporous support layer and the aqueous polyfunctional amine solution is preferably 1 second or more and 10 minutes or less, and more preferably 10 seconds or more and 3 minutes or less.

[0061] After bringing the aqueous solution of the polyfunctional amine into contact with the microporous support layer, sufficient liquid drainage is performed so that no droplets remain on the membrane. By performing sufficient liquid drainage, it is possible to prevent the remaining droplet portion from becoming a membrane defect and reducing the removal performance after the formation of the microporous support layer. As a method of liquid drainage, for example, as described in JP-A-2-78428, a method of holding the support membrane vertically after contact with the aqueous solution of the polyfunctional amine and allowing the excess aqueous solution to flow down naturally, or a method of forcibly draining the liquid by blowing an air stream such as nitrogen from an air nozzle can be used. Further, after liquid drainage, the membrane surface can be dried to partially remove the moisture of the aqueous solution.

[0062] In step (b), the concentration of the polyfunctional acid halide in the organic solvent solution is preferably in the range of 0.01% by mass or more and 10% by mass or less, and more preferably in the range of 0.02% by mass or more and 2.0% by mass or less. This is because a sufficient reaction rate can be obtained when the concentration is 0.01% by mass or more, and the occurrence of side reactions can be suppressed when the concentration is 10% by mass or less. Further, it is more preferable to contain an acylation catalyst in this organic solvent solution because interfacial polycondensation is promoted.

[0063] The organic solvent is preferably immiscible with water, dissolves the polyfunctional acid halide, and does not destroy the support membrane, and may be any one that is inert to the polyfunctional amine compound and the polyfunctional acid halide. Preferred examples include hydrocarbon compounds such as n-hexane, n-octane, n-decane, and isooctane.

[0064] The method of bringing the organic solvent solution of the polyfunctional acid halide into contact with the microporous support layer that has been brought into contact with the aqueous solution of the polyfunctional amine compound may be performed in the same manner as the method of coating the microporous support layer with the aqueous solution of the polyfunctional amine.

[0065] In step (c), it is preferable to heat the microporous support layer contacted with the organic solvent solution of the polyfunctional acid halide. The heat treatment temperature is, for example, preferably 50°C or higher and 180°C or lower, more preferably 60°C or higher and 160°C or lower. In order to obtain a high-density polyamide functional layer, 80°C or higher and 160°C or lower is even more preferable. The heating time varies depending on the temperature of the membrane surface which is the reaction field, but it is preferably 10 seconds or longer, more preferably 20 seconds or longer.

[0066] In step (d), it is preferable to wash the composite semipermeable membrane from which the organic solvent has been removed with hot water. The temperature of the hot water is preferably 40 to 95°C, more preferably 60 to 95°C. When the temperature of the hot water is 40°C or higher, unreacted substances and oligomers remaining in the membrane can be sufficiently removed. On the other hand, when the temperature of the hot water is 95°C or lower, the shrinkage degree of the composite semipermeable membrane does not increase, and good permeation performance can be maintained. Note that the preferable range of the temperature of the hot water can be appropriately adjusted according to the types and amounts used of the polyfunctional amine and polyfunctional acid halide.

[0067] In step (e), the partial structure represented by the above general formula (1), (2), (3) or (4) is imparted to the polyamide. As the method, a method (method A) of allowing an electrophilic reagent having the partial structure represented by the following (1) to act on the amino terminus of the polyamide using an appropriate condensing agent (or directly) can be mentioned. Thereby, a polyamide containing the partial structure represented by the general formula (2) is obtained.

[0068] Alternatively, the structure represented by (1) may be imparted to the polyamide by a multi-step reaction. In this case, the structure represented by (1) does not necessarily have to be included in the structure of the reaction reagent (method B). As a specific technique of method B, for example, a technique of allowing an electrophilic reagent having a vinyl group (reagent B1) to act on the amino terminus and then allowing a reagent having a sulfanyl group (reagent B2) to further act in the presence of an appropriate radical initiator can be mentioned. Thereby, a polyamide containing the partial structure represented by the general formula (3) is obtained.

[0069] Examples of the electrophilic reagent (Reagent A) used in Method A include 3-sulfanylpropionic acid, 4-sulfanylbutyric acid, 3-(methylsulfanyl)propionic acid, 4-(methylsulfanyl)butyric acid, and the like. These reagents may be used in the form of salts such as sodium salts and potassium salts. Examples of suitable condensing agents for use in the first step of Method A or Method B include 1-hydroxybenzotriazole, 1-hydroxy-7-azabenzotriazole, ethyl (hydroxyimino)cyanoacetate, (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate, (1-cyano-2-ethoxy-2-oxoethylideneaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride, and the like.

[0070] Examples of the electrophilic reagent (Reagent B1) used in the first-stage reaction of Method B include ω-unsaturated aliphatic carboxylic acids such as acrylic acid, 3-butenoic acid, 2-methyl-3-butenoic acid, 4-pentenoic acid, 5-hexenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-nonenoic acid, and aromatic carboxylic acids such as 4-vinylbenzoic acid. Reagent B1 is preferably an ω-unsaturated aliphatic carboxylic acid, more preferably acrylic acid. Examples of the reagent (Reagent B2) having a sulfanyl group used in the second-stage reaction of Method B include monothiols such as methanethiol, ethanethiol, 1-propanethiol, 2-propanethiol, 2-propen-1-thiol, thioacetic acid, 2-aminoethanethiol, thioglycol, thioglycolic acid, thiophenol, and polyfunctional thiols such as 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, bis(2-mercaptoethyl) ether, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, dithiothreitol, dithioerythritol, hexa(ethylene glycol) dithiol, 1,4-butanediol bis(thioglycolate), 1,3,5-benzenetrithiol, thiocyanuric acid, ethylene glycol bis(3-mercaptopropionate), isocyanuric acid tris[2-(3-mercaptopropionyloxy)ethyl], dipentaerythritol hexakis(3-mercaptopropionate). Reagent B2 is preferably a polyfunctional thiol, and thus can have a structure represented by the following general formula (3’) in which a plurality of amino groups are crosslinked.

[0071] [Chemical formula]

[0072] (R1 to R4 are hydrogen atoms or aliphatic chains having 1 to 10 carbon atoms, Ar1 to Ar3 are aromatic rings having 6 to 14 carbon atoms which may have substituents, L2 is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain heteroatoms, and X is a structure represented by the above general formula (4).) 3. Use of the composite semipermeable membrane The composite semipermeable membrane of the present invention is wound around a cylindrical water collecting pipe having a large number of holes together with a supply water flow path material such as a plastic net, a permeating water flow path material such as a tricot, and a film for enhancing pressure resistance as necessary, and is preferably used as a spiral-type composite semipermeable membrane element. Further, a composite semipermeable membrane module can be formed by connecting these elements in series or in parallel and housing them in a pressure vessel.

[0073] In addition, the above-mentioned composite semipermeable membrane, its element, and module can be combined with a pump for supplying supply water thereto, a device for pre-treating the supply water, etc. to constitute a fluid separation device. By using this separation device, supply water can be separated into permeated water such as drinking water and concentrated water that did not permeate through the membrane, and water suitable for the purpose can be obtained.

[0074] Examples of the supply water to be treated by the composite semipermeable membrane according to the present invention include liquid mixtures containing 500 mg / L or more and 100 g / L or less of TDS (Total Dissolved Solids) such as seawater, brackish water, and wastewater. Generally, TDS refers to the total amount of dissolved solids and is expressed as "mass ÷ volume" or "mass ratio". According to the definition, it can be calculated from the weight of the residue after evaporating the solution filtered through a 0.45-micron filter at a temperature of 39.5°C or higher and 40.5°C or lower, but more simply, it can be converted from the practical salinity (S).

[0075] Although the solute rejection rate improves with a higher operating pressure of the fluid separation device, the energy required for operation also increases. Also, considering the durability of the composite semipermeable membrane, the operating pressure when the water to be treated permeates through the composite semipermeable membrane is preferably 0.5 MPa or more and 10 MPa or less. Since the membrane permeation flux decreases as the supply water temperature decreases, it is preferably 5°C or higher. Also, since the solute rejection rate decreases as the temperature increases, it is preferably 28°C or lower. Further, when the supply water pH increases, in the case of supply water with a high solute concentration such as seawater, there is a risk of scale formation such as magnesium, and there is also concern about membrane deterioration due to high pH operation, so operation in the neutral range is preferred.

Example

[0076] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples at all.

[0077] The analysis of functional groups and composition and the residual rate of water in the examples and comparative examples were measured as follows. Unless otherwise specified, the operations were carried out at 25°C below.

[0078] (Zeta potential) The composite semipermeable membrane was cut into a 10 cm × 10 cm square and washed with distilled water. The washed composite semipermeable membrane was set in a cell for flat plate samples, and using the separation functional layer as the measurement surface, it was measured with an electrophoretic light scattering photometer (manufactured by Otsuka Electronics Co., Ltd.; ELS-8000) to obtain the zeta potential at pH 3 of the separation functional layer. Five measurement points were randomly selected, and their average was taken as the zeta potential (mV). The specific measurement conditions were as follows.

[0079] Monitoring particle: Polystyrene latex (hydroxypropyl cellulose coated) Measurement solution: Aqueous NaCl solution (10 mM) pH: 3 Temperature: 25°C Light source: He-Ne laser (Weight average molecular weight) The weight average molecular weight (polystyrene conversion) of PSf was measured using gel permeation chromatography (manufactured by Tosoh Corporation; HLC-8022). The specific measurement conditions were as follows.

[0080] Column: Two TSK gel SuperHM-H (manufactured by Tosoh Corporation; inner diameter 6.0 mm, length 15 cm) Eluent: LiBr / N-methylpyrrolidone solution (10 mM) Sample concentration: 0.1 mass% Flow rate: 0.5 mL / min Temperature: 40°C (NaCl removal rate) For the composite semipermeable membrane, evaluation water prepared at a NaCl concentration of 35,000 ppm, a boron concentration of 5 ppm, 25 °C, and pH 7 was supplied at an operating pressure of 5.5 MPa, and a membrane filtration test was conducted. The electrical conductivities of the evaluation water and the permeated water were measured with a multi-water quality meter (manufactured by Toa DKK Corporation; MM-60R) to obtain the respective NaCl concentrations (practical salinity). From the NaCl concentrations thus obtained, the NaCl rejection rate (%) was calculated based on the following formula (3).

[0081] NaCl rejection rate (%) = 100 × {1 - (NaCl concentration in permeated water / NaCl concentration in evaluation water)} ··· (Formula 3) (Boron rejection rate) In the membrane filtration test of "NaCl rejection rate", the boron concentrations in the evaluation water and the permeated water were measured with an ICP emission spectrometer (manufactured by Agilent Technologies; Agilent 5110), and the boron rejection rate (%) was calculated based on the following formula (4).

[0082] Boron rejection rate (%) = 100 × {1 - (boron concentration in permeated water / boron concentration in evaluation water)} ··· (Formula 4) (Membrane permeation flux) In the membrane filtration test of "NaCl rejection rate", the permeated water volume (m 3 ) was measured and converted to a value per unit membrane area (m 2 ) and per unit time (day), and the membrane permeation flux (m 3 / m 2 / day) was obtained.

[0083] (Chlorine resistance test) The composite semipermeable membrane was immersed in an aqueous solution of 25 mg / L sodium hypochlorite adjusted to pH 7.0 for 24 hours in an atmosphere of 25 °C. Then it was immersed in an aqueous solution of 1000 mg / L sodium bisulfite for 10 minutes and subsequently washed thoroughly with water.

[0084] The chemical resistance was determined from the membrane permeation flux ratio, SP ratio, and boron SP ratio before and after immersion.

[0085] Membrane permeation flux ratio = membrane permeation flux after immersion / membrane permeation flux before immersion SP ratio = (100 - salt removal rate after immersion) / (100 - salt removal rate before immersion) Boron SP ratio = (100 - boron removal rate after immersion) / (100 - boron removal rate before immersion) (Quantification of moisture content) Composite semipermeable membrane: 5 m 2 The substrate was physically peeled off, and the microporous support layer and the separation functional layer were recovered. While maintaining the wet state, they were added little by little to a beaker containing dichloromethane and stirred to dissolve the polymer constituting the microporous support layer. The insoluble matter in the beaker was recovered with filter paper. This insoluble matter was put into a beaker containing dichloromethane and stirred, and the insoluble matter in the beaker was recovered. This operation was repeated until the elution of the polymer forming the microporous support layer could not be detected in the dichloromethane solution. The recovered separation functional layer was dried with a vacuum dryer to remove the remaining dichloromethane. The obtained separation functional layer was made into a powdery sample by cryogenic grinding, and the mass was repeatedly measured in a glove box controlled at a relative humidity of 95% and a temperature of 25 °C until it became stable. The stable value of the mass was designated as y. Further, the separation functional layer sample was vacuum dried at 110 °C, and the dried sample was left standing in a glove box controlled at a relative humidity of 0% and a temperature of 25 °C. The mass of the separation functional layer was repeatedly measured until it became stable. The stable value of the mass was designated as z. At this time, the moisture content of the separation functional layer was determined by (y - z) / y.

[0086] The raw materials of the composite semipermeable membranes used in the examples and comparative examples are summarized below.

[0087] PSf (manufactured by Solvay Specialty Polymers; Udel P-3500, M w 80000) DMF (manufactured by Fujifilm Wako Pure Chemical Corporation) Polyester long fiber nonwoven fabric (thickness 90 μm, density 0.42 g / cm 3 ) m-PDA (manufactured by Fujifilm Wako Pure Chemical Corporation) TMC (manufactured by Fujifilm Wako Pure Chemical Corporation) Decane (manufactured by Fujifilm Wako Pure Chemical Corporation) Sodium bisulfite (manufactured by Fujifilm Wako Pure Chemical Corporation) Sodium acrylate (manufactured by FUJIFILM Wako Pure Chemical Corporation) Sodium 2-methyl-3-butenoate (manufactured by FUJIFILM Wako Pure Chemical Corporation) Sodium 4-vinylbenzoate (manufactured by FUJIFILM Wako Pure Chemical Corporation) 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (manufactured by FUJIFILM Wako Pure Chemical Corporation) Tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate (manufactured by FUJIFILM Wako Pure Chemical Corporation) Ethanethiol (manufactured by FUJIFILM Wako Pure Chemical Corporation) 2-Bromoethanethiol (manufactured by FUJIFILM Wako Pure Chemical Corporation) Ammonium persulfate (manufactured by FUJIFILM Wako Pure Chemical Corporation) Sodium thioglycolate (manufactured by FUJIFILM Wako Pure Chemical Corporation) (Preparation of the support membrane) A 16.0 mass% DMF solution of polysulfone (PSf) was cast at a thickness of 200 μm onto a polyester nonwoven fabric (air permeability 2.0 cc / cm 2 / sec), and immediately immersed in pure water and left for 5 minutes to prepare a support membrane.

[0088] (Comparative Example 1) The porous support membrane obtained by the above operation was immersed in a 3.0 mass% aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes, the support membrane was slowly pulled up in the vertical direction, nitrogen was blown from an air nozzle to remove the excess aqueous solution from the surface of the support membrane, and then a 25°C decane solution containing 0.165 mass% of trimesoyl chloride (TMC) was applied so that the surface was completely wetted and left standing for 1 minute. Then, the membrane was made vertical and the excess solution was drained off and removed to obtain a composite semipermeable membrane having a crosslinked aromatic polyamide separation functional layer. Thereafter, the composite semipermeable membrane was washed with hot water at 80°C for 2 minutes. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0089] (Comparative Example 2) The support film obtained by the above operation was immersed in a 3.0 mass% aqueous solution of m-phenylenediamine as a polyfunctional aromatic amine solution for 2 minutes, the support film was slowly pulled up in the vertical direction, and nitrogen was blown from an air nozzle to remove the excess aqueous solution from the surface of the support film. In an environment controlled at 45°C, a 45°C decane solution containing 0.2 mass% of TMC was applied so that the surface was completely wetted and allowed to stand for 10 seconds, then heated in an oven at 120°C for 10 minutes, and then the support film was made vertical to drain and remove the excess solution. Thus, a layer containing crosslinked aromatic polyamide was formed on the support film to obtain a composite semipermeable membrane. Thereafter, the composite semipermeable membrane was washed with hot water at 80°C for 2 minutes. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0090] (Example 1) For the composite semipermeable membrane obtained in Comparative Example 1, a mixed aqueous solution of 0.90 mass% sodium acrylate and 0.28 mass% 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride at 25°C was applied so that the surface was completely wetted and allowed to stand for 24 hours, and then immersed in distilled water at 25°C for 1 hour. Further, a mixed aqueous solution of 0.26 mass% tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, 0.11 mass% ammonium persulfate, and 0.17 mass% sodium thioglycolate adjusted to 70°C was applied so that the surface was completely wetted, and allowed to stand at 25°C for 1 hour. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0091] (Example 2) To the composite semipermeable membrane obtained in Comparative Example 1, an aqueous mixed solution of 1.22% by mass of sodium 2-methyl-3-butenoate and 0.28% by mass of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride at 25°C was applied so that the surface was completely wetted, and after standing for 24 hours, it was immersed in distilled water at 25°C for 1 hour. Further, an aqueous mixed solution of 0.26% by mass of tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, 0.11% by mass of ammonium persulfate, and 0.17% by mass of sodium thioglycolate adjusted to 70°C was applied so that the surface was completely wetted, and it was allowed to stand at 25°C for 1 hour. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0092] (Example 3) To the composite semipermeable membrane obtained in Comparative Example 1, an aqueous mixed solution of 1.70% by mass of sodium 4-vinylbenzoate and 0.28% by mass of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride at 25°C was applied so that the surface was completely wetted, and after standing for 24 hours, it was immersed in distilled water at 25°C for 1 hour. Further, an aqueous mixed solution of 0.26% by mass of tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, 0.11% by mass of ammonium persulfate, and 0.17% by mass of sodium thioglycolate adjusted to 70°C was applied so that the surface was completely wetted, and it was allowed to stand at 25°C for 1 hour. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0093] (Example 4) To the composite semipermeable membrane obtained in Comparative Example 1, an aqueous mixed solution of 0.90% by mass of sodium acrylate and 0.28% by mass of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride at 25°C was applied so that the surface was completely wetted, and after standing for 24 hours, it was immersed in distilled water at 25°C for 1 hour. Further, an aqueous mixed solution of 0.09% by mass of ethanethiol, 0.11% by mass of ammonium persulfate, and 0.17% by mass of sodium thioglycolate adjusted to 70°C was applied so that the surface was completely wetted, and it was allowed to stand at 25°C for 1 hour. Finally, it was immersed in distilled water at 25°C for 1 hour.

[0094] (Example 5) For the composite semipermeable membrane obtained in Comparative Example 1, an aqueous solution of 0.21% by mass of 2-bromoethanethiol at 80 °C was applied so that the surface was completely wetted, allowed to stand at 25 °C for 24 hours, and then immersed in distilled water at 25 °C for 1 hour.

[0095] (Example 6) For the composite semipermeable membrane obtained in Comparative Example 2, an aqueous mixed solution of 0.90% by mass of sodium acrylate and 0.28% by mass of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride at 25 °C was applied so that the surface was completely wetted, allowed to stand for 24 hours, and then immersed in distilled water at 25 °C for 1 hour. Further, an aqueous mixed solution of 0.26% by mass of tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, 0.11% by mass of ammonium persulfate, and 0.17% by mass of sodium thioglycolate adjusted to 70 °C was applied so that the surface was completely wetted, allowed to stand at 25 °C for 1 hour. Finally, it was immersed in distilled water at 25 °C for 1 hour.

[0096] The structures and performances of the above membranes are shown in Table 1 and Table 2. As shown in the examples, it can be seen that the composite semipermeable membrane of the present invention has high water permeation performance, removal performance, and high chlorine resistance.

[0097] [Table 1]

[0098] [Table 2] [Industrial Applicability]

[0099] The composite semipermeable membrane of the present invention can be suitably used for desalination of seawater, brackish water, wastewater, and the like. [Explanation of Symbols]

[0100] 1 Composite semipermeable membrane 2 Substrate 3 Microporous support layer 4 Separation functional layer 41 Thin film 42 Protrusion 43 Recess

Claims

1. A composite semipermeable membrane having a microporous support layer and a separation functional layer provided on the microporous support layer, wherein the separation functional layer contains a crosslinked aromatic polyamide as a main component, and the crosslinked aromatic polyamide has a partial structure represented by (2), the composite semipermeable membrane. 【Chemical 1】 (R １ ~R ４ is a hydrogen atom or an aliphatic chain having 1 to 10 carbon atoms, and Ar １ ~Ar ３ is an aromatic ring having 6 to 14 carbon atoms which may have a substituent, and L １ is a single bond or an aliphatic chain or an aromatic ring having 1 to 8 atoms which may contain a hetero atom, and X is an arbitrary atomic group which may contain a cross-linked structure.)

2. The composite semipermeable membrane according to claim 1, wherein the crosslinked aromatic polyamide has a partial structure represented by (3).

3. [Chemical Formula 2] (R １ ~R ４ is a hydrogen atom or an aliphatic chain having 1 to 10 carbon atoms, and Ar １ ~Ar ３ is an aromatic ring having 6 to 14 carbon atoms which may have a substituent, L ２ is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain a hetero atom, and X is an arbitrary atomic group which may contain a cross-linked structure.) The composite semipermeable membrane according to claim 1 or 2, wherein X in the structure is represented by (4).

4. The composite semipermeable membrane according to claim 2 or 3. 【Chemical Formula 3】 (R １ ~ R ４ is a hydrogen atom or an aliphatic chain having 1 to 10 carbon atoms, and Ar １ ~ Ar ３ is an aromatic ring having 6 to 14 carbon atoms which may have a substituent, L ３ is a single bond or an aliphatic chain or aromatic ring having 1 to 6 atoms which may contain a hetero atom, and Y is an arbitrary atomic group.)

5. The L of the structure (3) ２ and the L of (4) ３ is a single bond or an aliphatic chain having 1 to 6 carbon atoms which may contain a hetero atom The composite semipermeable membrane according to any one of claims 2 to 4.

6. The L of the said structure (3) ２ and the L of (4) ３ is a single bond The composite semipermeable membrane according to any one of claims 1 to 5, wherein the zeta potential at pH 3 is 0 mV or less.

7. The composite semipermeable membrane according to any one of claims 1 to 6, wherein the following value x for the separation functional layer extracted from the composite semipermeable membrane satisfies x ≦ 0.

80. x = z / y y: mass at a relative humidity of 95% and a temperature of 25°C z: mass at a relative humidity of 0% and a temperature of 25°C ​ ​ ​ ​

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