Method for preserving composite semipermeable membrane, preservation solution, and spiral 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-type 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 in ultrapure water production, seawater desalination, brackish water desalination, wastewater reuse, 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, the water permeability may drop significantly or the blocking performance may change compared to before drying. For this reason, the spiral membrane element has been transported, stored, etc. in a state where pure water or an aqueous solution containing propylene glycol is enclosed as a storage liquid.

[0004] However, in the case of composite semipermeable membranes having a separation functional layer formed of polyamide resins containing components derived from piperazine, in particular, the water permeability tends to decrease during transportation or storage in high temperature environments (e.g., 40°C or higher).For this reason, membrane elements are transported and stored in refrigerated (reefer) containers, which causes problems such as high transportation and storage costs and increased environmental load.

[0005] On the other hand, as such a preservation solution, Patent Document 1 proposes a preservation solution consisting of an aqueous solution mainly composed of an inorganic salt for use in a microfiltration (MF) membrane or an ultrafiltration (UF) membrane. In addition, it is said that the inorganic salt is preferably one that exhibits anti-freezing, antibacterial and antifungal properties in addition to preventing the membrane from drying out. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-142191 A 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 for use in 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, stored in a high-temperature environment, etc., because the pore sizes differ greatly.

[0008] Therefore, an object of the present invention is 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, and a preservation solution used therefor.

[0009] Another object of the present invention is to provide a spiral membrane element in which the 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 into solving 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 therethrough, comprising: A method for preserving a composite semipermeable membrane, comprising using an aqueous solution containing an inorganic salt and / or an organic salt consisting of only monovalent cations and monovalent anions 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 unlikely to decrease in water permeability even in a high-temperature environment. The details of the reason are unclear, but it is thought to be as follows. In other words, a composite semipermeable membrane that selectively allows monovalent ions to pass through is likely to diffuse monovalent cations and monovalent anions in the separation functional layer when in contact with a storage solution, and even if it is placed in a high-temperature environment (e.g., 40°C or higher) in that state, it is thought that the separation functional layer is unlikely to shrink or undergo microstructural changes, and the water permeability is unlikely to decrease. In contrast, when a salt containing divalent ions is used, the divalent ions are localized on the surface of the separation functional layer, which enhances the effect of draining water from the separation functional layer by forward osmosis, and promotes the decrease in water permeability.

[0014] [2] The composite semipermeable membrane comprises a porous support and a separation functional layer formed of a polyamide-based resin on the porous support, and the polyamide-based resin contains a component derived from piperazine. The method for storing the composite semipermeable membrane described in [1].

[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 terms of the storage stability of the composite semipermeable membrane in a high-temperature environment and its relationship with the permeating ion size of the separation functional layer.

[0016] [3] The monovalent cation is NH4 + ,Na + , and K + and the monovalent anion is selected from the group consisting of Cl. - ,HCOO - ,CH3COO - ,HCO3 - , and NO3 - and the inorganic salt and / or the organic salt has a molecular weight of 101 or less.

[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 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, it is possible to more reliably prevent the water permeability of the composite semipermeable membrane 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 making the preservation solution further contain the above-mentioned chemicals, it is possible to inhibit the proliferation of bacteria during storage.

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

[0023] By using such a storage solution, the composite semipermeable membrane is less likely to experience a decrease in water permeability even during transportation, storage, etc. in a high-temperature environment.

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

[0025] According to the above spiral-wound membrane element, since the above storage solution is used, the permeability of the composite semipermeable membrane is unlikely to decrease even in a high-temperature environment. The reason is as described in [1]. In addition, the effects of the following [8] to

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

[0026] [8] The spiral membrane element described in [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-based resin, the polyamide-based resin containing a component derived from piperazine.

[0027] [9] The monovalent cation is NH4 + ,Na + , and K + and the monovalent anion is selected from the group consisting of Cl. - ,HCOO - ,CH3COO - ,HCO3 - , and NO3 - and the inorganic salt and / or the organic salt has a molecular weight of 101 or less.

[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 mass % or more.

[0029]

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

[10] , wherein the storage solution further contains a chemical having a bacteriostatic or bactericidal effect. Effect 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 permeability of the composite semipermeable membrane is unlikely to decrease even in a high-temperature environment, and a storage solution used therefor. It is also possible to provide a spiral-wound membrane element, in which the permeability of the composite semipermeable membrane is unlikely to decrease even when transported, stored, etc. in a high-temperature environment. [Brief description of the drawings]

[0031] [Figure 1] FIG. 2 is a partially cutaway perspective view showing an example of a spiral membrane element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 permeates 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 - ) were 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 is preferably provided with a porous support and a separation functional layer formed of a polyamide resin on the porous support, 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 is to bring the composite semipermeable membrane into contact with a specific preservation solution, and the method for bringing the composite semipermeable membrane into contact with the preservation solution includes a method for bringing the composite semipermeable membrane into contact in the state of a spiral-type membrane element and a method for bringing the composite semipermeable membrane into contact 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 bringing the membrane element into contact with the preservation solution is preferred.

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

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

[0039] The contact state between the composite semipermeable membrane and the storage solution is preferably 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] The storage of the composite semipermeable membrane is a concept including the maintenance of the state of the composite semipermeable membrane during transportation, storage, movement, standby of the composite semipermeable membrane or a membrane element having the same, etc. In addition, 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 + From the viewpoint of environmental load, one or more cations selected from the group consisting of Na + , 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 - From the viewpoint of low corrosivity, 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, from the viewpoint of maintaining the rejection rate of MgSO4 and water permeability, NaCl, NH4Cl, NaNO3, HCOONa, and CH3COONa are particularly preferable.

[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 the 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 the organic salt is preferably 20 or more, and more preferably 40 or more.

[0047] Moreover, the molecular weight (g / mol ion number) of the monovalent cation 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 number) of the monovalent anion 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 preservation solution contains water, but may contain a solvent other than water, and examples of such a solvent 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. Also, 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, from the viewpoint of cost.

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

[0051] The content of the chemical in the preservation solution is preferably 0.1 to 2.0% by mass, and 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. The composite semipermeable membrane is provided with a porous support and a separation functional layer formed of a polyamide resin on the porous support, 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 including, 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 reacting, more specifically polymerizing (polycondensing), polyfunctional amines (A) and (B) with polyfunctional acid halides. Of these, structural unit (C) formed by reacting aliphatic polyfunctional amine (B) with polyfunctional acid halides and structural unit (D) formed by reacting aromatic polyfunctional amine (A) with polyfunctional acid halides, the former tends to be more flexible and the latter tends to be more rigid.

[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 easily obtaining a composite semipermeable membrane that selectively permeates monovalent ions.

[0056] The polyfunctional amine is an amine having two or more reactive amino groups, for example, 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, and more preferably m-phenylenediamine. In addition, when the compound group includes two or more aromatic polyfunctional amines (A), it is preferable 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 is, 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 a nitrogen atom of piperazine is substituted with a substituent. The substituent is, for example, an alkyl group having 1 to 4 carbon atoms, an amino group, or a hydroxyl group. Since it is a polyfunctional amine, when a hydrogen atom bonded to a nitrogen atom is substituted, the substituent is an amino group. The piperazine derivative is, for example, 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 an alicyclic polyfunctional acid halide described below.

[0063] The alicyclic polyfunctional acid halide is not particularly limited, and is, for example, 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, about 0.01 to 0.4 μm. The material of the microporous layer is, for example, polyarylethersulfone such as polysulfone and polyethersulfone; polyimide; and polyvinylidene fluoride. Among them, polysulfone and polyarylethersulfone are preferred because of 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, and 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, and preferably 20 to 75 μm.

[0065] The method of forming the separation functional layer on the porous support is not particularly limited, and known methods can be adopted. The method of forming the separation functional layer is, for example, an interfacial condensation method, a phase separation method, and a thin film coating method. The interfacial condensation method is a method of forming a separation functional layer composed of polyamide by contacting an amine aqueous solution containing a polyfunctional amine with an organic acid halide solution containing a polyfunctional acid halide, and proceeding with a reaction (polycondensation) between the polyfunctional amine and the polyfunctional acid halide at the contact surface (interface). The formation of the separation functional layer by this interfacial condensation can be performed on the porous support, and in this case, the separation functional layer is formed directly on the porous support. Of course, the separation functional layer formed at a place other than the porous support, for example, on a transfer substrate, may 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 publicly known publications 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 onto the porous support to bring it into contact with the coating layer and 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 mass%, preferably 1 to 4 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 mass%, preferably 0.05 to 3 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 of the organic solvent 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, and more preferably a saturated hydrocarbon having a boiling point of 200° C. or less.

[0069] The time from coating the amine aqueous solution on the porous support to coating the acid halide organic solution is about 1 to 180 seconds, preferably 2 to 120 seconds, more preferably 2 to 40 seconds, and particularly preferably 2 to 10 seconds, depending on the composition and viscosity of the amine aqueous solution and the pore size on the surface of the porous support. If the coating interval between the two is excessively long, the amine aqueous solution may penetrate and diffuse deep into the porous support before the acid halide organic solution is coated, and a large amount of unreacted polyfunctional amine may remain in the porous support. In addition, the unreacted polyfunctional amine that has penetrated deep into the porous support tends to be difficult to remove even by a subsequent cleaning treatment. On the other hand, if the coating interval between the two is excessively short, the amine aqueous solution hardly penetrates into the porous support before the acid halide organic solution is coated, and the excess amine aqueous solution exists on the porous support, which may deteriorate the characteristics of the formed separation functional layer.

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

[0071] In addition to the polyfunctional amines (A) and (B) and polyfunctional acid halides, the compound group may contain various additives for the purpose of facilitating the formation of the separation functional layer and improving the properties of the composite semipermeable membrane obtained. The additives may be added, for example, to the amine aqueous solution and / or the acid halide organic solution in the interfacial condensation method. Some types of additives remain in the formed separation functional layer and contribute, for example, to 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, and polyvinyl alcohol is 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 the inside of the formed separation functional layer by copolymerization with the polyfunctional amine and the polyfunctional acid halide. This can further improve 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 cation exchange catalysts 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 required.

[0074] For example, the additive is a salt of a tetraalkylammonium halide or trialkylammonium with an organic acid. This salt has the effect of facilitating the formation of a separation functional layer, improving the absorbency of an amine aqueous solution into a 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 necessary.

[0075] The thickness of the separation functional layer is not particularly limited, and is usually about 0.05 to 2 μm, and 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. It may be a single layer of separation functional 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 effect of the present invention can be obtained, the separation functional layer may contain a material other than polyamide. In this case, the separation functional layer is a layer mainly composed of polyamide. The main component is 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 further subjected to chlorine treatment. The chlorine treatment may further improve the permeation flux of the composite semipermeable membrane by removing parts 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, which is a layer composed of a polymer. When a coating layer that is a hydrophilic layer is provided, the hydrophilicity of the composite semipermeable membrane surface is improved, and the permeation flux of the composite semipermeable membrane is further improved. The coating layer is preferably provided on the surface of the composite semipermeable membrane on the separation functional layer side.

[0080] The polymer used in the coating layer is not particularly limited as long as it does not dissolve the separation functional layer and the porous support and does not dissolve during use of the composite semipermeable membrane (e.g., 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 having 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 above polymer is dissolved and drying it.

[0081] The coating layer may have a crosslinked structure with the polyamide constituting the separation functional layer. In this case, the 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, and for example, the composite semipermeable membrane having a polyvinyl alcohol layer formed on the surface of the separation 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, an organic crosslinking agent such as an epoxy compound and a polycarboxylic acid, and / or an inorganic crosslinking agent such as a boron compound may be used as a crosslinking agent.

[0082] (Spiral type 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, the composite semipermeable membrane being a composite semipermeable membrane that selectively allows monovalent ions to pass therethrough, and characterized in that 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 explained above, any of the configurations of conventional membrane elements can be adopted.

[0083] 1, the spiral-type membrane element includes a perforated central tube 5 and a wound body R including 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 liquid, and the membrane element can be preserved (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 the membrane element. For example, even if the membrane element is immersed in the storage liquid and then the storage liquid is allowed to flow naturally 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 liquid may further include a packaging bag, a packaging container, a cap for sealing the ends, an end covering material, and the like.

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

[0087] It is also possible to form the supply side flow path and / or the permeate 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 supply side flow path material 2 and / or the permeate 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 side ends on both sides in the axial direction A1 of the membrane leaf L with an adhesive. The outer peripheral sealed portion 12 is formed by sealing the end of 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 becomes a permeate side 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 part in which the perforated central tube 5 and the base end sides of both end sealing parts of the membrane leaf L are sealed with an adhesive. The membrane leaf L and the supply side flow path material 2 are wound around the central tube 5 via such a central sealing part 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 spiral-type membrane element with a diameter of 8 inches, about 15 to 30 sets of membrane leaves L are wound. When the membrane element is used, it is housed in a pressure container (vessel), and a feed liquid 7 is supplied from one end face side 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 as a concentrated liquid 9 from the other end face side of the membrane element. In addition, the permeated liquid 8 that permeates the separation membrane 1 while the feed liquid 7 flows along the feed-side flow path material 2 flows along the permeation-side flow path material 3, then flows into the central tube 5 from the opening 5a, and is discharged from the end of the central tube 5.

[0092] The feed-side flow passage material 2 generally has a role of securing gaps for uniformly supplying the fluid to the membrane surface. For example, a net, a knitted material, or an unevenly processed sheet can be used as the feed-side flow passage material 2, and a material having a maximum thickness of about 0.1 to 3 mm can be used as needed. When flow passage materials are provided on both sides of the separation membrane 1, it is common to use different flow passage materials as the feed-side flow passage material 2 on the feed liquid side and the permeate-side flow passage material 3 on the permeate side. It is preferable to use a thick, coarse-meshed net-like flow passage material for the feed-side flow passage material 2, while using a fine-meshed woven or knitted flow passage material for the permeate-side flow passage material 3.

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

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

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

[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 rate 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 the conditions of a water temperature of 25°C ± 1°C, a membrane load of 15 GFD (gallons / ft / day), and a recovery rate (permeate volume / raw water flow rate) of 15%, and then the permeate was sampled and subjected to ion analysis using an ion concentration measuring device (ICS-6000 manufactured by Thermo Fisher Scientific Co., Ltd.) and the rejection rates of various ions were calculated using the following formula. Rejection rate (%) = {1 - (ion concentration in permeate [mg / L]) / (average of ion concentrations in feed and concentrate [mg / L])} x 100 As a result, the commercially available membrane element used in Example 1 etc. had a low concentration of monovalent ions (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 higher rejection rate. Therefore, the composite semipermeable membrane used was a composite semipermeable membrane that selectively allowed the passage of monovalent ions.

[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 10 minutes or more 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 liquid was measured using a conductivity measuring device (manufactured by Yamagata Toa DKK, CM-41X), and the rejection of MgSO4 was calculated from the results and the calibration curve (concentration-conductivity) based on 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 circulation 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 for the permeate flow rate ratio (-) is 0.95 or more.

[0102] Example 1 A commercially available spiral-wound membrane element (PRO-XS2, manufactured by Nitto Denko Corporation) with a composite semipermeable membrane (NF membrane) that selectively allows monovalent ions to pass through was used, and after immersion for 60 seconds in an aqueous solution (storage solution) containing 3.5% by mass of NaCl, the membrane element was removed, and excess storage solution was allowed to drip from the membrane element while the membrane element was in an upright position. The membrane element was then bagged, and the inside of the bag was suctioned to vacuum pack it. This was placed in an oven at a temperature of 50°C and stored for 27 days, and the MgSO4 rejection rate, permeate flow rate, and permeate flow rate ratio before and after storage were evaluated. 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 the storage solution shown in Table 2 was used and the storage temperature and number of days shown in Table 2 were used, and the MgSO4 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-type membrane element (PRO-XS1, manufactured by Nitto Denko Corporation) was used as the membrane element, and the membrane element was stored in the same manner as in Example 1, and the MgSO4 rejection rate, permeate flow rate, and permeate flow rate ratio were evaluated before and after storage. 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 mass%) as the main raw material (Safeguard 100, manufactured by Kurita Water Industries Ltd.) was used as the storage solution and the membrane element was stored at the storage temperature and for the number of days shown in Table 2. The MgSO4 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 membrane element was stored at the storage temperature and for the storage period shown in Table 2. The MgSO4 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 composite semipermeable membrane was less likely to experience a decrease in water permeability 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, the composite semipermeable membrane experienced a decrease in water permeability in a high-temperature environment. In Comparative Example 1 in which a storage solution mainly made of propylene glycol was used, the decrease in 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 preserving a composite semipermeable membrane, the preservation solution thereof, and the spiral-type membrane element having the preservation 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, A method for storing a composite semipermeable membrane, wherein the monovalent cation is one or more cations selected from the group consisting of NH 4 + , Na + , and K + , the monovalent anion is one or more anions selected from the group consisting of Cl − , HCOO − , CH 3 COO − , HCO 3 − , 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. A preservation solution used in a method for preserving a composite semipermeable membrane described in 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, A spiral membrane element, wherein the monovalent cation is one or more cations selected from the group consisting of NH 4 + , Na + , and K + , the monovalent anion is one or more anions selected from the group consisting of Cl − , HCOO − , CH 3 COO − , HCO 3 − , 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, the polyamide-based resin containing 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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