Method for storing composite semipermeable membrane, storage solution, and spiral-wound membrane element

Abstract

To provide a method for preserving a composite semipermeable membrane which is less likely to cause a decrease in the water permeability of the composite semipermeable membrane even in a high-temperature environment, a preservation solution used for the method, and a spiral membrane element including the preservation solution.SOLUTION: The present invention provides a method for preserving a composite semipermeable membrane that allows monovalent ions to selectively permeate therethrough. The method uses an aqueous solution containing an inorganic salt and / or an organic salt composed only of monovalent cations and monovalent anions as a preservation solution to be brought into contact with the composite semipermeable membrane.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for preserving a composite semipermeable membrane using a preservation solution, the preservation solution, and a spiral-wound membrane element (hereinafter sometimes abbreviated as "membrane element") having the preservation solution. [Background technology]

[0002] Composite semipermeable membranes are called RO (reverse osmosis) membranes, NF (nanofiltration) membranes, or FO (forward osmosis) membranes depending on their filtration performance and treatment method, and can be used for ultrapure water production, seawater desalination, desalination of brackish water, wastewater recycling, etc. In particular, composite semipermeable membranes that selectively allow monovalent ions to pass through are used as NF membranes to separate and remove divalent ion salts such as magnesium sulfate.

[0003] When a typical composite semipermeable membrane is dried after passing water through it, its water permeability may drop significantly compared to before drying, and its blocking performance may change. For this reason, the spiral-wound membrane element has been transported and stored with a storage liquid such as pure water or an aqueous solution containing propylene glycol sealed in the element.

[0004] However, composite semipermeable membranes with a separation functional layer made of polyamide resins containing piperazine-derived components tend to have a tendency to lose water permeability during transportation or storage in high-temperature environments (e.g., above 40°C). For this reason, membrane elements are transported and stored in refrigerated (reefer) containers, which poses problems such as high transportation and storage costs and increased environmental impact.

[0005] On the other hand, Patent Document 1 proposes a preservation solution consisting of an aqueous solution mainly composed of an inorganic salt for use in microfiltration (MF) membranes or ultrafiltration (UF) membranes. It is also stated that the inorganic salt is preferably one that not only prevents the membrane from drying out but also exhibits antifreeze, antibacterial, and antifungal properties. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-142191 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in Patent Document 1, it was unclear whether the aqueous solution proposed as a storage solution to be used for microfiltration (MF) membranes or ultrafiltration (UF) membranes would have the effect of suppressing the deterioration of water permeability when composite semipermeable membranes with significantly different pore sizes are transported or stored in a high-temperature environment, because the pore sizes differ greatly.

[0008] Therefore, an object of the present invention is to provide a method for storing a composite semipermeable membrane, which is less likely to cause a decrease in the water permeability of the composite semipermeable membrane even in a high-temperature environment, and a storage solution to be used therefor.

[0009] Another object of the present invention is to provide a spiral membrane element in which the water permeability of the composite semipermeable membrane is unlikely to decrease even when transported, stored, etc. in a high-temperature environment. [Means for solving the problem]

[0010] As a result of extensive research to solve the above-mentioned problems, the inventors discovered that in order to maintain water permeability in a high-temperature environment, the relationship between the ion size of the components contained in the storage solution and the permeating ion size of the separation functional layer of the composite semipermeable membrane is important, and that the above-mentioned object can be achieved by selecting an appropriate ion size for the former, thereby completing the present invention.

[0011] That is, the present invention includes the following.

[0012] [1] A method for storing a composite semipermeable membrane that selectively allows monovalent ions to pass through, comprising: A method for preserving a composite semipermeable membrane, wherein an aqueous solution containing an inorganic salt and / or an organic salt consisting only of monovalent cations and monovalent anions is used as a preservation solution to be brought into contact with the composite semipermeable membrane.

[0013] According to the above-mentioned storage method, the composite semipermeable membrane is less likely to experience a decrease in water permeability, even in a high-temperature environment. While the details of the reason for this are unclear, it is thought to be as follows: A composite semipermeable membrane that selectively allows monovalent ions to pass through it easily diffuses monovalent cations and monovalent anions into the separation functional layer when in contact with a storage solution. Even if the membrane is placed in a high-temperature environment (e.g., 40°C or higher) in this state, the separation functional layer is less likely to shrink or undergo microstructural changes, making it less likely to experience a decrease in water permeability. In contrast, when a salt containing divalent ions is used, the divalent ions are localized on the surface of the separation functional layer, enhancing the effect of draining water from the separation functional layer by forward osmosis, which is thought to promote a decrease in water permeability.

[0014] [2] The composite semipermeable membrane according to [1], wherein the composite semipermeable membrane comprises a porous support and a separation functional layer formed on the porous support from a polyamide resin, and the polyamide resin contains a component derived from piperazine.

[0015] In the case of a separation functional layer formed of a polyamide resin containing a component derived from piperazine, the effects of the present invention tend to be particularly pronounced in relation to the storage stability of the composite semipermeable membrane in a high-temperature environment and the permeable ion size of the separation functional layer.

[0016] [3] The monovalent cation is NH4 + ,Na + , and K + and the monovalent anion is one or more cations selected from the group consisting of Cl. - ,HCOO - ,CH3COO - ,HCO3 - , and NO3 - The method for preserving a composite semipermeable membrane according to [1] or [2], wherein the inorganic salt and / or the organic salt is one or more anions selected from the group consisting of:

[0017] In particular, the inorganic salt and / or the organic salt is HCOO as described above. - ,CH3COO - In the case of a salt containing ions, the effect of the present invention can be more easily obtained while suppressing the corrosiveness of the freshwater production facility.

[0018] [4] The method for preserving a composite semipermeable membrane according to any one of [1] to [3], wherein the concentration of the inorganic salt and / or the organic salt in the preservation solution is 0.5% by mass or more.

[0019] At such a concentration, the water permeability of the composite semipermeable membrane is more reliably prevented from decreasing.

[0020] [5] The method for preserving a composite semipermeable membrane according to any one of [1] to [4], wherein the preservation solution further contains a chemical having a bacteriostatic or bactericidal effect.

[0021] By using a preservative solution that further contains the above-mentioned chemicals, bacterial growth can be suppressed during storage.

[0022] [6] The preservation solution used in the method for preserving the composite semipermeable membrane according to any one of [1] to [5].

[0023] By using such a storage solution, the water permeability of the composite semipermeable membrane is less likely to decrease even when the membrane is transported or stored in a high-temperature environment.

[0024] [7] A spiral membrane element having a composite semipermeable membrane and a storage solution in contact with the composite semipermeable membrane, The composite semipermeable membrane is a composite semipermeable membrane that selectively allows monovalent ions to pass through, The storage solution is an aqueous solution containing an inorganic salt and / or an organic salt consisting of only monovalent cations and monovalent anions.

[0025] According to the spiral-wound membrane element, the use of the storage solution makes it difficult for the composite semipermeable membrane to lose its water permeability even in a high-temperature environment. The reason for this is as described in [1]. Furthermore, the effects of the following items [8] to

[11] are as described in [2] to [5].

[0026] [8] The spiral membrane element according to [7], wherein the composite semipermeable membrane comprises a porous support and a separation functional layer formed on the porous support and made of a polyamide resin, and the polyamide resin contains a component derived from piperazine.

[0027] [9] The monovalent cation is NH4 + ,Na + , and K + and the monovalent anion is one or more cations selected from the group consisting of Cl. - ,HCOO - ,CH3COO - ,HCO3 - , and NO3 - The spiral membrane element according to [7] or [8], wherein the inorganic salt and / or the organic salt is one or more anions selected from the group consisting of:

[0028]

[10] The spiral membrane element according to any one of [7] to [9], wherein the concentration of the inorganic salt and / or the organic salt in the storage solution is 0.5% by mass or more.

[0029]

[11] The spiral membrane element according to any one of [7] to

[10] , wherein the preservative solution further contains a chemical having a bacteriostatic or bactericidal effect. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a method for storing a composite semipermeable membrane, in which the water permeability of the composite semipermeable membrane is unlikely to decrease even in a high-temperature environment, and a storage solution used therefor, and it is also possible to provide a spiral-wound membrane element, in which the water permeability of the composite semipermeable membrane is unlikely to decrease even when transported, stored, etc. in a high-temperature environment. [Brief explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a partially cutaway perspective view showing an example of a spiral membrane element. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, an embodiment of the present invention will be described.

[0033] (Storage method for composite semipermeable membrane) The method for preserving a composite semipermeable membrane of the present invention is directed to a composite semipermeable membrane that selectively permeates monovalent ions. Here, "selectively permeating monovalent ions" refers to selectively permeating monovalent ions over divalent ions, and can be specifically determined as follows.

[0034] That is, according to the evaluation method of "(1) Rejection rate of various ions using simulated seawater" in the examples, the monovalent ions (Na + , K. + , and Cl - ) are all less than 50% and divalent ions (Mg 2+ , and SO4 2- ) is equivalent to a composite semipermeable membrane that selectively allows the passage of monovalent ions.

[0035] Such a composite semipermeable membrane preferably comprises a porous support and a separation functional layer formed on the porous support from a polyamide resin, the polyamide resin preferably containing a component derived from piperazine. The composite semipermeable membrane will be described in detail later.

[0036] The method for preserving a composite semipermeable membrane of the present invention involves contacting the composite semipermeable membrane with a specific preservation solution, and examples of the method for contacting the composite semipermeable membrane with a preservation solution include a method for contacting the composite semipermeable membrane in the state of a spiral membrane element and a method for contacting the composite semipermeable membrane in the state of a composite semipermeable membrane. However, from the viewpoint of being able to maintain a good contact state by a simple process, the method for contacting the membrane with a preservation solution in the state of a membrane element is preferred.

[0037] Methods for contacting the membrane element with the storage solution include immersing the membrane element in the storage solution, supplying the storage solution to the supply-side flow path of the membrane element, and allowing part of the storage solution to permeate during this process. After contacting the membrane element with the storage solution, part of the storage solution may be removed from the membrane element, or the storage solution may be sealed inside the membrane element with the storage solution present in part or all of the flow path. In this case, the membrane element may be vacuum-suctioned and packaged.

[0038] In addition, examples of a method for contacting a composite semipermeable membrane with a preservation solution include a method in which the composite semipermeable membrane is formed, then continuously immersed in the preservation solution, and then wound up; a method in which the composite semipermeable membrane formed in a roll shape is continuously immersed in the preservation solution while being unwound; and a method in which the preservation solution is sprayed or allowed to flow down onto the composite semipermeable membrane.

[0039] It is preferable that the contact state between the composite semipermeable membrane and the storage solution is maintained until membrane separation is performed. From this viewpoint, a method of packaging or sealing the membrane element in a state in which the composite semipermeable membrane and the storage solution are in contact with each other is preferred, and a method of packaging or sealing the membrane element in a vacuum suction state is particularly preferred.

[0040] Note that storage of a composite semipermeable membrane is a concept that includes maintaining the state of the composite semipermeable membrane during transportation, storage, movement, standby operation, etc. of the composite semipermeable membrane or a membrane element having the same. Furthermore, the present invention enables storage of the composite semipermeable membrane or membrane element in a high-temperature environment, for example, at 40°C or higher, particularly at 45 to 55°C.

[0041] The preservation solution to be brought into contact with the composite semipermeable membrane may be any of the preservation solutions described below. That is, the preservation solution of the present invention is used in the method for preserving a composite semipermeable membrane of the present invention.

[0042] (preservation solution) In the present invention, it is preferable to use an aqueous solution containing an inorganic salt and / or an organic salt consisting of only monovalent cations and monovalent anions as the storage solution to be brought into contact with the composite semipermeable membrane.

[0043] Examples of monovalent cations constituting inorganic salts and / or organic salts include monovalent metal ions such as alkali metal ions and ammonium ions, and NH4 + ,Li + ,Na + , and K + Preferably, one or more cations selected from the group consisting of: + , and K + is more preferred.

[0044] Examples of monovalent anions constituting the inorganic salt and / or the organic salt include monovalent inorganic ions such as halogen ions, hydrogen carbonate ions, nitrate ions, and hydrogen sulfite ions, and monovalent organic acid ions such as organic carboxylate ions. - ,HCOO - ,CH3COO - ,HCO3 - , and NO3 - Preferably, one or more anions selected from the group consisting of CH3COO - ,HCOO - is more preferred.

[0045] As the inorganic salt and / or the organic salt, NaCl, NH4Cl, NaNO3, HCOONa, and CH3COONa are particularly preferred from the viewpoint of maintaining the water permeability while maintaining the rejection rate of MgSO4.

[0046] From the viewpoint of maintaining the water permeability of the composite semipermeable membrane in a high-temperature environment, the molecular weight of the inorganic salt and / or organic salt is preferably 101 or less, more preferably 98 or less, and even more preferably 84 or less. The lower limit of the molecular weight of the inorganic salt and / or organic salt is preferably 20 or more, more preferably 40 or more.

[0047] Furthermore, the molecular weight (g / mol ion) of the monovalent cations constituting the inorganic salt and / or organic salt is preferably 40 or less, more preferably 25 or less, from the viewpoint of maintaining the water permeability of the composite semipermeable membrane in a high-temperature environment. The molecular weight (g / mol ion) of the monovalent anions constituting the inorganic salt and / or organic salt is preferably 65 or less, more preferably 45 or less, from the viewpoint of maintaining the water permeability of the composite semipermeable membrane in a high-temperature environment.

[0048] The preservative solution contains water, but may contain a solvent other than water, and examples of such solvents include alcohols such as ethylene glycol, glycerin, and propylene glycol.

[0049] The concentration of the inorganic salt and / or organic salt in the storage solution is preferably 0.5% by mass or more, more preferably 1% by mass or more, from the viewpoint of maintaining the water permeability of the composite semipermeable membrane in a high-temperature environment, and from the viewpoint of cost, the concentration of the inorganic salt and / or organic salt in the storage solution is preferably 5% by mass or less, more preferably 4% by mass or less, particularly preferably 2% by mass or less.

[0050] Furthermore, the preservative solution preferably contains a chemical with a bacteriostatic or bactericidal effect, such as SBS (sodium bisulfite), formaldehyde, hypochlorous acid compounds or hydrogen peroxide, or benzoic acid.

[0051] The content of the chemical in the preservative solution is preferably 0.1 to 2.0% by mass, more preferably 0.5 to 1.0% by mass, from the viewpoint of bacteriostatic or bactericidal effect.

[0052] (composite semipermeable membrane) The composite semipermeable membrane is a composite semipermeable membrane that selectively allows monovalent ions to pass through. It comprises a porous support and a separation functional layer formed on the porous support from a polyamide resin, and the polyamide resin preferably contains a component derived from piperazine. More preferably, the polyamide resin contains a component derived from piperazine and a component derived from trimesic acid trichloride.

[0053] The separation functional layer is composed of a polyamide formed by the reaction of a compound group containing, for example, an aliphatic polyfunctional amine (B), or an aromatic polyfunctional amine (A) and an aliphatic polyfunctional amine (B), and a polyfunctional acid halide. Here, in the compound group, the proportion of the aromatic polyfunctional amine (A) in the polyfunctional amine is preferably less than 5 mol%, more preferably less than 1 mol%, and particularly preferably 0 mol%.

[0054] This polyamide has structural units formed by the reaction, more specifically, polymerization (polycondensation) of polyfunctional amines (A) and (B) with polyfunctional acid halides. Of these, structural unit (C) formed by the reaction of aliphatic polyfunctional amine (B) with polyfunctional acid halides and structural unit (D) formed by the reaction of aromatic polyfunctional amine (A) with polyfunctional acid halides tend to be more flexible and more rigid than structural unit (D).

[0055] The proportion of the aliphatic polyfunctional amine (B) in the polyfunctional amines in the compound group is preferably 95 mol% or more, more preferably 99 mol% or more, and particularly preferably 100 mol%, from the viewpoint of making it easier to obtain a composite semipermeable membrane that selectively permeates monovalent ions.

[0056] The polyfunctional amine is an amine having two or more reactive amino groups, such as a diamine having two reactive amino groups. The compound group may contain two or more aromatic polyfunctional amines (A) or two or more aliphatic polyfunctional amines (B).

[0057] The aromatic polyfunctional amine (A) is not particularly limited and may be, for example, at least one selected from m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, N,N'-dimethyl-m-phenylenediamine, 2,4-diaminoanisole, amideol, and xylylenediamine. The aromatic polyfunctional amine (A) is preferably at least one selected from m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine, with m-phenylenediamine being more preferred. Furthermore, when the compound group includes two or more aromatic polyfunctional amines (A), it is preferred that the polyfunctional amine (A) includes m-phenylenediamine.

[0058] The aliphatic polyfunctional amine (B) is, for example, an alicyclic polyfunctional amine. In this case, the permeation flux can be improved to a higher level by combining it with the aromatic polyfunctional amine (A).

[0059] The alicyclic polyfunctional amine (B) is not particularly limited and may be, for example, at least one selected from 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, and piperazine and its derivatives. The alicyclic polyfunctional amine (B) is preferably piperazine or a piperazine derivative. Here, the piperazine derivative refers to a compound in which at least one hydrogen atom bonded to a carbon atom or nitrogen atom of piperazine is substituted with a substituent. Examples of the substituent include an alkyl group having 1 to 4 carbon atoms, an amino group, and a hydroxyl group. Since this is a polyfunctional amine, if a hydrogen atom bonded to a nitrogen atom is substituted, the substituent is an amino group. Examples of the piperazine derivative include at least one selected from 2,5-dimethylpiperazine and 4-aminomethylpiperazine.

[0060] The polyfunctional acid halide is an acid halide having two or more reactive carbonyl groups. The polyfunctional acid halide may be an aromatic polyfunctional acid halide or an aliphatic polyfunctional acid halide. The aliphatic polyfunctional acid halide may be an alicyclic polyfunctional acid halide. The compound group may contain two or more polyfunctional acid halides. When the compound group contains a polyfunctional acid halide having a valence of three or more, a separation functional layer composed of a polyamide having a crosslinked structure can be formed.

[0061] The aromatic polyfunctional acid halide is not particularly limited, and is, for example, at least one selected from trimesic acid trichloride, terephthalic acid dichloride, isophthalic acid dichloride, biphenyldicarboxylic acid dichloride, naphthalenedicarboxylic acid dichloride, benzenetrisulfonic acid trichloride, benzenedisulfonic acid dichloride, and chlorosulfonylbenzenedicarboxylic acid dichloride.

[0062] The aliphatic polyfunctional acid halide is not particularly limited, and is, for example, at least one selected from propanedicarboxylic acid dichloride, butanedicarboxylic acid dichloride, pentanedicarboxylic acid dichloride, propanetricarboxylic acid trichloride, butanetricarboxylic acid trichloride, pentanetricarboxylic acid trichloride, glutaryl halide, adipoyl halide, and the alicyclic polyfunctional acid halides described below.

[0063] The alicyclic polyfunctional acid halide is not particularly limited, and examples thereof include at least one selected from cyclopropanetricarboxylic acid trichloride, cyclobutanetetracarboxylic acid tetrachloride, cyclopentanetricarboxylic acid trichloride, cyclopentanetetracarboxylic acid tetrachloride, cyclohexanetricarboxylic acid trichloride, tetrahydrofurantetracarboxylic acid tetrachloride, cyclopentanedicarboxylic acid dichloride, cyclobutanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride.

[0064] The configuration of the porous support is not limited as long as a separation functional layer can be formed thereon. The porous support is, for example, an ultrafiltration membrane in which a microporous layer is formed on a nonwoven fabric. The average pore size of the microporous layer is, for example, approximately 0.01 to 0.4 μm. Materials for the microporous layer include, for example, polyarylethersulfones such as polysulfone and polyethersulfone; polyimides; and polyvinylidene fluoride. Among these, polysulfones and polyarylethersulfones are preferred due to their high chemical, mechanical, and thermal stability. The porous support may be a self-supporting support made of a thermosetting resin such as an epoxy resin. In this case, the porous support has an average pore size of, for example, 0.01 to 0.4 μm. The thickness of the porous support is not particularly limited and is, for example, 10 to 200 μm, preferably 20 to 75 μm.

[0065] The method for forming the separation functional layer on the porous support is not particularly limited, and known methods can be used. Examples of methods for forming the separation functional layer include interfacial condensation, phase separation, and thin film coating. The interfacial condensation method involves contacting an aqueous amine solution containing a polyfunctional amine with an organic acid halide solution containing a polyfunctional acid halide, thereby promoting a reaction (polycondensation) between the polyfunctional amine and the polyfunctional acid halide at the contact surface (interface) to form a separation functional layer composed of polyamide. The formation of the separation functional layer by this interfacial condensation can be carried out on the porous support, in which case the separation functional layer is formed directly on the porous support. Of course, a separation functional layer formed on a location other than the porous support, such as a transfer substrate, can also be placed on the porous support. Details of the interfacial condensation method are described, for example, in JP-A-58-24303 and JP-A-1-180208, and the conditions described in these known documents can be appropriately adopted. In the phase separation method and thin film coating method, methods described in known literature can also be used.

[0066] The separation functional layer is preferably formed by applying an aqueous amine solution containing a polyfunctional amine component onto a porous support to form an aqueous solution coating layer, and then applying an organic acid halide solution containing a polyfunctional acid halide to the porous support to bring it into contact with the coating layer, thereby allowing interfacial polymerization to proceed.

[0067] In this method, the concentration of the polyfunctional amine in the aqueous amine solution is not particularly limited, and is, for example, 0.1 to 10% by mass, preferably 1 to 4% by mass. In addition, the concentration of the polyfunctional acid halide in the organic acid halide solution is not particularly limited, and is, for example, 0.01 to 5% by mass, preferably 0.05 to 3% by mass.

[0068] The organic solvent used in the acid halide organic solution is not particularly limited as long as it has low solubility in water, does not deteriorate the porous support, and dissolves the polyfunctional acid halide, and examples thereof include saturated hydrocarbons such as cyclohexane, heptane, octane, and nonane; and halogen-substituted hydrocarbons such as 1,1,2-trichlorotrifluoroethane. The organic solvent is preferably a saturated hydrocarbon having a boiling point of 300°C or less, more preferably a saturated hydrocarbon having a boiling point of 200°C or less.

[0069] The time between applying the aqueous amine solution to the porous support and applying the organic acid halide solution varies depending on the composition and viscosity of the aqueous amine solution and the pore size of the surface of the porous support, but is typically about 1 to 180 seconds, preferably 2 to 120 seconds, more preferably 2 to 40 seconds, and particularly preferably 2 to 10 seconds. If the application interval between the two solutions is too long, the aqueous amine solution may penetrate and diffuse deep into the porous support before the organic acid halide solution is applied, resulting in a large amount of unreacted polyfunctional amine remaining in the porous support. Furthermore, unreacted polyfunctional amine that has penetrated deep into the porous support tends to be difficult to remove even by subsequent washing. On the other hand, if the application interval between the two solutions is too short, the aqueous amine solution may barely penetrate the porous support before the organic acid halide solution is applied, resulting in the presence of excess aqueous amine solution on the porous support, which may result in a deterioration in the properties of the resulting separation functional layer.

[0070] In this method, it is preferable to contact the coating layer of the aqueous amine solution formed on the porous support with the organic acid halide solution, remove excess organic solution present on the porous support, and heat-dry the film formed on the porous support to form a separation functional layer. Heat-drying can improve the mechanical strength and heat resistance of the separation functional layer. The heat-drying temperature is, for example, 70 to 200°C, preferably 80 to 130°C. The heating time is, for example, about 30 seconds to 10 minutes, preferably about 40 seconds to 7 minutes.

[0071] In addition to the polyfunctional amines (A) and (B) and polyfunctional acid halides, the compounds may contain various additives to facilitate the formation of the separation functional layer or to improve the properties of the resulting composite semipermeable membrane. The additives may be added, for example, to the aqueous amine solution and / or the organic acid halide solution used in the interfacial condensation method. Some additives remain in the formed separation functional layer, contributing to, for example, improving the properties of the composite semipermeable membrane.

[0072] The additive is, for example, a hydrophilic polymer. That is, the compound group may further include a hydrophilic polymer. The hydrophilic polymer is, for example, at least one selected from polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid, with polyvinyl alcohol being preferred. When the separation functional layer is formed by the interfacial condensation method, the polyfunctional amine aqueous solution may contain a hydrophilic polymer such as polyvinyl alcohol. The hydrophilic polymer improves the hydrophilicity of the surface and interior of the formed separation functional layer by copolymerization with the polyfunctional amine and the polyfunctional acid halide. This further improves the permeation flux of the composite semipermeable membrane. The amount of the additive added is preferably about 0.01 to 20% by mass, more preferably 0.05 to 5% by mass.

[0073] Other additives include, for example, surfactants such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium lauryl sulfate that improve the wettability of the solution to the porous support; basic compounds such as sodium hydroxide, trisodium phosphate, and triethylamine that remove hydrogen halides produced by the reaction of polyfunctional amines with polyfunctional acid halides; acylation catalysts that catalyze the reaction; and cellulose acetates having a solubility parameter of 8 to 14 (cal / cm), as described in JP-A-8-224452. 3 ) 1 / 2 These compounds may be added to the aqueous amine solution as needed.

[0074] The additive may be, for example, a salt of a tetraalkylammonium halide or trialkylammonium with an organic acid. This salt has the effects of facilitating the formation of a separation functional layer, improving the absorbability of an amine aqueous solution into the porous support, and promoting the reaction between a polyfunctional amine and a polyfunctional acid halide. This salt may be added to the amine aqueous solution as needed.

[0075] The thickness of the separation functional layer is not particularly limited, and is usually about 0.05 to 2 μm, preferably 0.1 to 1 μm. It is preferable that the thickness of the separation functional layer is uniform.

[0076] The shape of the separation functional layer is not particularly limited, and may be a single layer formed on a porous support, or may be a separation functional layer having a "double pleat structure" as described in JP 2011-189340 A.

[0077] The separation functional layer is a layer made of polyamide. As long as the effects of the present invention are obtained, the separation functional layer may contain materials other than polyamide. In this case, the separation functional layer is a layer whose main component is polyamide. The main component refers to the component with the highest content, and the content is usually 50% by mass or more, and more preferably 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more in that order. The separation functional layer may be a layer made of polyamide.

[0078] The composite semipermeable membrane of the present invention may be a membrane that has been further subjected to chlorine treatment. Chlorine treatment may further improve the permeation flux of the composite semipermeable membrane by, for example, removing portions of the polyamide with unstable bonds.

[0079] A coating layer may be provided on the surface of the composite semipermeable membrane of the present invention. The coating layer is, for example, a nonionic hydrophilic layer, and is a layer composed of a polymer. When a hydrophilic coating layer is provided, the hydrophilicity of the composite semipermeable membrane surface is improved, thereby further improving the permeation flux of the composite semipermeable membrane. The coating layer is preferably provided on the surface of the composite semipermeable membrane on the separating functional layer side.

[0080] The polymer used for the coating layer is not particularly limited as long as it does not dissolve the separating functional layer and the porous support and does not leach out when the composite semipermeable membrane is used (for example, during water treatment). The polymer is, for example, at least one selected from polyvinyl alcohol, polyvinylpyrrolidone, hydroxypropyl cellulose, polyethylene glycol, and saponified ethylene-vinyl acetate copolymer. The polymer is preferably polyvinyl alcohol, and particularly preferably polyvinyl alcohol with a saponification degree of 99% or more. The coating layer can be formed on the surface of the composite semipermeable membrane, for example, by immersing the composite semipermeable membrane in a solution in which the polymer is dissolved and then drying.

[0081] The coating layer may have a crosslinked structure with the polyamide constituting the separating functional layer. In this case, elution of the coating layer during use of the composite semipermeable membrane can be suppressed. The coating layer having a crosslinked structure with the polyamide is, for example, a layer containing polyvinyl alcohol having a degree of saponification of 90% or more. The method for crosslinking the polyvinyl alcohol and the polyamide is not particularly limited. For example, a composite semipermeable membrane having a polyvinyl alcohol layer formed on the surface of the separating functional layer may be immersed in a polyaldehyde solution acidified with hydrochloric acid. The polyaldehyde is, for example, a dialdehyde such as glutaraldehyde or terephthalaldehyde. Instead of or together with the polyaldehyde, organic crosslinking agents such as epoxy compounds and polycarboxylic acids, and / or inorganic crosslinking agents such as boron compounds may be used as crosslinking agents.

[0082] (Spiral membrane element) The spiral membrane element of the present invention is a spiral membrane element having a composite semipermeable membrane and a storage solution in contact with the composite semipermeable membrane, wherein the composite semipermeable membrane is a composite semipermeable membrane that selectively allows monovalent ions to pass therethrough, and the storage solution of the present invention is used as the storage solution. Therefore, with the exception of the use of the composite semipermeable membrane and storage solution as described above, any of the configurations of conventional membrane elements can be adopted.

[0083] 1, the spiral-wound membrane element comprises, for example, a perforated central tube 5 and a wound body R containing a separation membrane 1 (composite semipermeable membrane) wound around the central tube 5. In the present invention, in the membrane element, the separation membrane 1 is in contact with a storage solution, and the membrane element can be stored (transported, stored, etc.) in this state.

[0084] Such contact between the separation membrane 1 and the storage liquid can be achieved by the method described above as a method for contacting the storage liquid in the state of a membrane element. For example, even if the membrane element is immersed in the storage liquid and then the storage liquid is allowed to naturally flow down from the end, the storage liquid is retained in the separation membrane 1, the feed-side channel material 2 between the membrane leaves L, or the permeate-side channel material 3 within the membrane leaves L, and the separation membrane 1 can maintain a state of contact with the storage liquid.

[0085] The membrane element containing the storage solution may further include a packaging bag, a packaging container, caps for sealing the ends, end covering materials, and the like.

[0086] 1 includes a plurality of membrane leaves L, each having a permeate-side channel material 3 interposed between opposing separation membranes 1, a feed-side channel material 2 interposed between the membrane leaves L, a perforated central tube 5 around which the membrane leaves L and the feed-side channel material 2 are wound, and a sealing portion 12 that prevents mixing of the feed-side channel and the permeate-side channel. In this case, the permeate-side channel in the membrane leaf L can be formed by the permeate-side channel material 3 (also referred to as the permeate-side spacer).

[0087] It is also possible to form the feed-side flow path and / or the permeation-side flow path in the separation membrane 1 itself by providing irregularities or grooves on the surface of the separation membrane 1, in which case the feed-side flow path material 2 and / or the permeation-side flow path material 3 can be omitted.

[0088] 1 shows an example in which the sealed portion includes both end sealed portions and an outer peripheral sealed portion 12. Of the sealed portions, the both end sealed portions are formed by sealing two edge portions on both sides of the membrane leaf L in the axial direction A1 with an adhesive. The outer peripheral sealed portion 12 is formed by sealing the edge portion at the outer peripheral tip of the membrane leaf L with an adhesive. The area surrounded by the opposing separation membrane 1, the both end sealed portions, and the outer peripheral sealed portion 12 forms a permeate flow path, which is structured to communicate with the opening 5a of the central tube 5.

[0089] It is also preferable to have a central sealing portion in which the perforated central tube 5 and the base end sides of both end sealing portions of the membrane leaf L are sealed with an adhesive. The membrane leaf L and the feed-side channel material 2 are wound around the central tube 5 via such a central sealing portion to form a wound body R. The adhesive is not particularly limited, and any conventionally known adhesive such as a urethane adhesive or an epoxy adhesive can be used.

[0090] A first end member 10 having a function such as a seal carrier may be provided on the upstream side of the membrane element wound body R, and a second end member 20 having a function such as an anti-telescope material may be provided on the downstream side.

[0091] In a typical 8-inch diameter spiral membrane element, about 15 to 30 sets of membrane leaves L are wound. When the membrane element is in use, it is housed in a pressure vessel, and a feed liquid 7 is supplied from one end face of the membrane element. The supplied feed liquid 7 flows along the feed-side flow path material 2 in a direction parallel to the axial direction A1 of the central tube 5 and is discharged from the other end face of the membrane element as a concentrated liquid 9. In addition, permeated liquid 8, which permeates the separation membrane 1 as the feed liquid 7 flows along the permeation-side flow path material 3, flows through the permeation-side flow path material 3, and then flows into the central tube 5 through the openings 5a and is discharged from the end of the central tube 5.

[0092] The feed-side channel material 2 generally serves to ensure gaps for uniformly supplying the fluid to the membrane surface. For example, nets, knitted fabrics, textured sheets, etc. can be used as this feed-side channel material 2, and materials with a maximum thickness of approximately 0.1 to 3 mm can be used as needed. Furthermore, when channel materials are placed on both sides of the separation membrane 1, different channel materials are generally used: the feed-side channel material 2 on the feed liquid side and the permeate-side channel material 3 on the permeate side. It is preferable to use a thick, coarse-mesh net-like channel material for the feed-side channel material 2, while using a fine-mesh woven or knitted channel material for the permeate-side channel material 3.

[0093] When RO membranes or NF membranes are used in applications such as seawater desalination and wastewater treatment, the permeate-side channel material 3 is provided so as to be interposed between opposing separation membranes 1 in the membrane leaf L. This permeate-side channel material 3 is required to support the pressure applied to the membrane from the backside of the membrane and to ensure a channel for the permeate 8.

[0094] In order to ensure such a function, the permeate-side channel material 3 is preferably formed of a tricot knit fabric, and more preferably, the tricot knit fabric is subjected to resin impregnation reinforcement or fusion treatment after the knit fabric is formed.

[0095] As the separation membrane 1, the above-mentioned composite semipermeable membrane that selectively allows monovalent ions to permeate is used.

[0096] In the case of a typical spiral membrane element, an outer periphery of the wound body R is provided with an exterior material 15. The exterior material 15 is not particularly limited, and examples thereof include various sheets, films, tapes, etc., and, if necessary, a fiber-reinforced resin (FRP) or the like is used for reinforcement. A preferred method for forming the fiber-reinforced resin is to use roving, in which fibers are impregnated with a curable resin, and wrap this around the outer periphery of the wound body R. [Example]

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

[0098] [Evaluation and measurement methods] (1) Rejection rates of various ions using simulated seawater Simulated seawater was prepared (pH was left as is) with the composition shown in Table 1. This simulated seawater was used as raw water and circulated for 10 minutes or more through the commercially available membrane element used in Example 1 etc. under conditions of a water temperature of 25°C ± 1°C, a membrane load of 15 GFD (gallons per foot per day), and a recovery rate (permeate volume / raw water flow rate) of 15%, after which the permeate was sampled and subjected to ion analysis using an ion concentration measuring device (ICS-6000 manufactured by Thermo Fisher Scientific), and the rejection rates of various ions were calculated using the following formula. Rejection rate (%) = {1 - (ion concentration in permeate [mg / L]) / (average ion concentration of feed and concentrate [mg / L])} x 100 As a result, the commercially available membrane element used in Example 1 etc. was evaluated by the above-mentioned method to measure the monovalent ion (Na + , K. + , Cl - ) The blocking rate was 50% or less (Na + =21%, K + =23%, Cl - =25% (catalog value)) and divalent ions (Mg 2+ , SO4 2- ) had a larger rejection rate. Therefore, the composite semipermeable membrane used was a composite semipermeable membrane that selectively allowed monovalent ions to pass through.

[0099] [Table 1]

[0100] (2) Rejection rate of MgSO4 The rejection (salt rejection) of the membrane element before and after storage was determined as follows. Using the membrane element before and after storage, a magnesium sulfate (MgSO4) aqueous solution (concentration 2000 ppm, temperature 25°C ± 1°C, pH 6.5-7.0) was circulated and permeated for at least 10 minutes at an operating pressure of 0.76 MPa and a recovery rate (permeate volume / raw water flow rate) of 15%. The conductivity of the membrane permeate and feed solution was measured using a conductivity measuring device (Yamagata Toa DKK, CM-41X). The MgSO4 rejection was calculated from the results and the calibration curve (concentration-conductivity) using the following formula: Rejection rate = (1 - (MgSO4 concentration in membrane permeate / (average of MgSO4 concentrations in feed and concentrate)) x 100 (%)

[0101] (3) Permeated water flow rate, permeated water flow rate ratio The flow rate (GPD (gallons per day)) of the membrane permeate after circulating for 10 minutes or more when measuring the above "(2) MgSO4 rejection rate" was measured. In addition, the permeate flow rate ratio of the membrane element before and after storage was calculated based on the following formula. Permeate flow rate ratio (-) = Permeate flow rate after storage (GPD) / Permeate flow rate before storage (GPD) The target value of the permeate flow rate ratio (-) is 0.95 or more.

[0102] Example 1 A commercially available spiral-wound membrane element (Nitto Denko Corporation, PRO-XS2) with a composite semipermeable membrane (NF membrane) that selectively permeates monovalent ions was used. It was immersed in an aqueous solution (storage solution) containing 3.5% by mass of NaCl for 60 seconds, then removed. The membrane element was then held upright and the excess storage solution was allowed to drip off. The membrane element was then placed in a bag, and the inside of the bag was vacuum-packed. This was then stored in an oven at 50°C for 27 days. The MgSO4 rejection, permeate flow rate, and permeate flow rate ratio were evaluated before and after storage. The results are shown in Table 2.

[0103] Examples 2 to 14 The membrane element was stored in the same manner as in Example 1, except that it was stored using the storage solution shown in Table 2 and at the storage temperature and for the number of days shown in Table 2, and the MgSO rejection, permeate flow rate, and permeate flow rate ratio were evaluated before and after storage. The results are shown in Table 2.

[0104] Example 15 In Example 1, a commercially available spiral-wound membrane element (PRO-XS1, manufactured by Nitto Denko Corporation) was used as the membrane element. The membrane element was stored in the same manner as in Example 1, and the MgSO rejection, permeate flow rate, and permeate flow rate ratio before and after storage were evaluated. The results are shown in Table 2. The composite semipermeable membrane used was a composite semipermeable membrane that selectively allowed monovalent ions to pass through, based on the evaluation results of the rejection rates of various ions using simulated seawater.

[0105] Comparative Example 1 The membrane element was stored in the same manner as in Example 1, except that an aqueous solution containing propylene glycol (2% by mass, manufactured by Kurita Water Industries Ltd.) was used as the storage solution and stored at the storage temperature and for the number of days shown in Table 2. The MgSO rejection, permeate flow rate, and permeate flow rate ratio were evaluated before and after storage. The results are shown in Table 2.

[0106] Comparative Examples 2 to 4 The membrane element was stored in the same manner as in Example 1, except that a storage solution containing divalent ions as shown in Table 2 was used and the storage temperature and number of days were shown in Table 2. The MgSO rejection, permeate flow rate, and permeate flow rate ratio were evaluated before and after storage. The results are shown in Table 2.

[0107] [Table 2]

[0108] As shown in the results in Table 2, in Examples 1 to 15, in which an aqueous solution containing an inorganic salt and / or an organic salt consisting only of monovalent cations and monovalent anions was used as the storage solution, the water permeability of the composite semipermeable membrane was less likely to decrease even in a high-temperature environment.

[0109] In contrast, in Comparative Examples 2 to 4, in which an aqueous solution containing divalent ions was used as the storage solution, a decrease in the water permeability of the composite semipermeable membrane occurred in a high-temperature environment. Also, in Comparative Example 1, in which a storage solution mainly made of propylene glycol was used, the decrease in the water permeability of the composite semipermeable membrane in a high-temperature environment was slightly suppressed, but the effect of suppressing the decrease in water permeability was not sufficient. [Industrial Applicability]

[0110] According to the method for storing a composite semipermeable membrane, the storage solution therefor, and the spiral membrane element containing the storage solution of the present invention, the permeability of the composite semipermeable membrane is unlikely to decrease even in a high-temperature environment, and there is no need to transport and store the membrane element in a refrigerated (reefer) container, which is industrially advantageous in terms of transportation and storage costs and environmental load. [Explanation of symbols]

[0111] 1: Separation membrane (composite semipermeable membrane) 5: Central tube A1: Axial direction R: Rolled body

Claims

1. A method for storing a composite semipermeable membrane that selectively allows monovalent ions to pass therethrough, comprising: As a storage solution to be brought into contact with the composite semipermeable membrane, an aqueous solution containing an inorganic salt and / or an organic salt consisting of only monovalent cations and monovalent anions is used, The monovalent cation is NH ４ ＋ , Na ＋ , and K ＋ and the monovalent anion is one or more cations selected from the group consisting of Cl － , HCOO － , CH ３ COO － , and NO ３ － and the inorganic salt and / or the organic salt has a molecular weight of 101 or less.

2. The composite semipermeable membrane according to claim 1, wherein the composite semipermeable membrane comprises a porous support and a separation functional layer formed on the porous support and made of a polyamide-based resin, and the polyamide-based resin contains a constituent component derived from piperazine.

3. The method for preserving a composite semipermeable membrane according to claim 1 , wherein the concentration of the inorganic salt and / or the organic salt in the preservation solution is 0.5% by mass or more.

4. The method for preserving a composite semipermeable membrane according to claim 1 , wherein the preservation solution further contains a chemical having a bacteriostatic or bactericidal effect.

5. The preservation solution used in the method for preserving the composite semipermeable membrane according to any one of claims 1 to 4.

6. A spiral membrane element having a composite semipermeable membrane and a storage solution in contact with the composite semipermeable membrane, The composite semipermeable membrane is a composite semipermeable membrane that selectively allows monovalent ions to pass through, the preservative solution is an aqueous solution containing an inorganic salt and / or an organic salt consisting of only monovalent cations and monovalent anions, The monovalent cation is NH ４ ＋ , Na ＋ , and K ＋ and the monovalent anion is one or more cations selected from the group consisting of Cl － , HCOO － , CH ３ COO － , and NO ３ － and the inorganic salt and / or the organic salt has a molecular weight of 101 or less.

7. 7. The spiral membrane element according to claim 6, wherein the composite semipermeable membrane comprises a porous support and a separation functional layer formed on the porous support and made of a polyamide-based resin, and the polyamide-based resin contains a constituent component derived from piperazine.

8. 7. The spiral membrane element according to claim 6, wherein the concentration of the inorganic salt and / or the organic salt in the storage solution is 0.5% by mass or more.

9. 7. The spiral membrane element according to claim 6, wherein the preservative solution further contains a chemical having a bacteriostatic or bactericidal effect.

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