Membrane cleaning solution and membrane cleaning method

Abstract

A film cleaning solution which contains a solvent and a metal removing agent, wherein: two or more kinds of solvents are contained; and the distance between the Hansen solubility parameter of this film cleaning solution and the Hansen solubility parameter of dimethylacetamide is 1.0 or less.

Description

[Technical Field]

[0001] The present invention relates to a membrane cleaning solution and a method for cleaning a membrane. This application claims priority based on Japanese Patent Application No. 2020-190859, filed on November 17, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] Conventionally, various membranes have been used for applications such as filters. For cleaning the membrane, various cleaning solutions are selected depending on the type of dirt. For example, metal impurities as contaminants on the membrane are generally removed by washing with an acid such as hydrochloric acid. For organic contaminants, a cleaning solution containing a solvent capable of removing the organic matter is selected.

[0003] For example, Patent Document 1 discloses a cleaning liquid for polyimide resin membranes, which is used to remove dirt (organic residues) derived from the membrane material, and which contains at least one solvent selected from the group consisting of hydroxyaliphatic carboxylic acid esters, aliphatic carboxylic acid esters, linear or cyclic ketones, alkylene glycol monoalkyl ethers, alkylene glycol monoalkyl ether acetates, and aprotic polar solvents other than these solvents. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-202479 Summary of the Invention [Problem to be solved by the invention]

[0005] When cleaning organic residues derived from membrane materials, such as the polyimide resin membrane cleaning solution shown in Patent Document 1, it is common to use different membrane cleaning solutions depending on the membrane material. For example, membranes made of polar resins such as polyimide are generally cleaned using a cleaning solution containing a polar solvent such as dimethylacetamide (DMAc), while membranes made of non-polar resins such as polyethylene are generally cleaned using a cleaning solution containing a non-polar solvent such as a hydrocarbon solvent.

[0006] On the other hand, as the requirements for the membranes to be cleaned increase, the cleaning performance required for the membrane cleaning solution also increases. Specifically, there is a need for a membrane cleaning solution that can remove organic residues derived from membrane materials and metal impurities derived from metal catalysts used in resin synthesis, regardless of the membrane material. Regarding metal impurities, there is also a need for a membrane cleaning solution that is highly effective in removing calcium, which causes membrane blockage (clogging).

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a membrane cleaning solution and a membrane cleaning method that can remove both organic residues and metal impurities regardless of the membrane material. [Means for solving the problem]

[0008] In order to solve the above problems, the present inventors have conducted extensive research focusing on the Hansen solubility parameter of membrane cleaning solutions and metal removers. As a result, they have discovered that by bringing the Hansen solubility parameter of a membrane cleaning solution closer to that of DMAc, which is commonly used to clean polyimide membranes, and by adding a metal remover, the solution has good cleaning properties not only for polyimide membranes, but also for polyethylene membranes, which have properties significantly different from those of polyimide membranes, and have thus completed the present invention. More specifically, the present invention employs the following:

[0009] A first aspect of the present invention is a membrane cleaning solution containing a solvent and a metal remover, wherein the membrane cleaning solution contains two or more solvents, and the distance between the Hansen solubility parameter of the membrane cleaning solution and the Hansen solubility parameter of dimethylacetamide (hereinafter simply referred to as "HSP distance") is 1.0 or less.

[0010] A second aspect of the present invention is a method for cleaning a membrane, comprising bringing the membrane cleaning solution according to the first aspect into contact with the membrane to clean the membrane. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a membrane cleaning solution and a membrane cleaning method that can remove both organic residues and metal impurities regardless of the membrane material. DETAILED DESCRIPTION OF THE INVENTION

[0012] (membrane cleaning solution) The membrane cleaning solution of this embodiment contains two or more solvents and a metal remover.

[0013] <Solvent> The membrane cleaning solution of this embodiment contains two or more solvents. The solvent can be appropriately selected from known organic solvents so that the HSP distance of the membrane cleaning solution of this embodiment is 1.0 or less. Specific examples of the solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, nitrile solvents, amide solvents, ether solvents, sulfoxide solvents, and sulfone solvents; and nonpolar solvents such as hydrocarbon solvents. As will be described later, some organic solvents contain multiple types of functional groups that characterize the above-mentioned solvents in their structure, and in such cases, the term "solvent" refers to any solvent containing the functional groups contained in the organic solvent. For example, diethylene glycol monomethyl ether is considered to be both an alcohol solvent and an ether solvent in the above classification.

[0014] <Ketone solvents> Ketone solvents are organic solvents that contain the C—C(═O)—C structure. Specific examples of ketone solvents include 1-octanone, 2-octanone, 1-nonanone, 2-nonanone, acetone, 4-heptanone, 1-hexanone, 2-hexanone, diisobutyl ketone, phenylacetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetonylacetone, ionone, diacetonyl alcohol, acetylcarbinol, acetophenone, methyl naphthyl ketone, and methyl amyl ketone (2-heptanone). The ketone solvent may also be a cyclic ketone solvent, specific examples of which include cyclohexanone (CH), methylcyclohexanone, isophorone, propylene carbonate, ethylene carbonate, and dihydrolevoglucosenone (silene).

[0015] <Ester-based solvents> Ester solvents are organic solvents that contain the C—C(═O)—O—C structure. Specific examples of ester solvents include methyl acetate, butyl acetate, ethyl acetate, isopropyl acetate, amyl acetate, isoamyl acetate, ethyl methoxyacetate, ethyl ethoxyacetate, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monopropyl ether acetate, diethylene glycol monophenyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, 2-methoxybutyl acetate, 3-methoxybutyl acetate, 4-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutyl acetate, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, 2 -Ethoxybutyl acetate, 4-ethoxybutyl acetate, 4-propoxybutyl acetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate, 4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate, 3-methyl-3-methoxypentyl acetate, 3-methyl-4-methoxypentyl acetate, 4-methyl-4-methoxypentyl acetate, propylene glycol diacetate, methyl formate, ethyl formate, butyl formate, propyl formate, ethyl lactate, butyl lactate, lactic acid Propyl, ethyl carbonate, propyl carbonate, butyl carbonate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, butyl pyruvate, methyl acetoacetate, ethyl acetoacetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl 2-hydroxypropionate, ethyl 2-hydroxypropionate, methyl-3-methoxypropionate, ethyl-3-methoxypropionate, ethyl-3-ethoxypropionate, propyl-3-methoxypropionate, and the like. The ester solvent may also be a cyclic ester solvent (lactone solvent). Specific examples of the lactone solvent include γ-butyrolactone (GBL), ε-caprolactone, γ-valerolactone, and δ-valerolactone.

[0016] <Alcohol-based solvents> Alcohol-based solvents are organic solvents that contain an alcoholic hydroxy group in their structure. An "alcoholic hydroxy group" means a hydroxy group bonded to a carbon atom of an aliphatic hydrocarbon group. Specific examples of alcohol solvents include 2-propanol (isopropyl alcohol), 1-butanol (n-butanol), 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol, 2-octanol, 3-hexanol, 3-heptanol, 3-octanol, 4-octanol, benzyl alcohol, ethylene glycol, diethylene glycol, propylene glycol (PG), and dipropylene glycol.

[0017] <Nitrile solvents> Nitrile solvents are organic solvents that contain a nitrile group in their structure. Specific examples of the nitrile solvent include acetonitrile, propionitrile, valeronitrile, and butyronitrile.

[0018] <Amide-based solvents> An amide solvent is an organic solvent that contains an amide group in its structure. Specific examples of amide solvents include chain amide solvents such as dimethylacetamide (DMAc), dimethylformamide, and tetramethylurea; and cyclic amide (lactam) solvents such as dimethylimidazolidinone, N-methylpyrrolidone, 1-ethyl-2-pyrrolidone, and 1-butyl-2-pyrrolidone.

[0019] ≪Ether solvents≫ Ether solvents are organic solvents that contain COC in their structure. Specific examples of ether solvents include ethylene glycol monomethyl ether (EGME), ethylene glycol isopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether (PGEE), propylene glycol monopropyl ether, propylene glycol monobutyl ether, and diisopropylene glycol monomethyl ether.

[0020] <Sulfoxide solvents> Sulfoxide solvents are organic solvents that contain a sulfinyl group -S(=O)- in their structure. Specific examples of sulfoxide solvents include dimethyl sulfoxide (DMSO).

[0021] <Sulfone solvents> Sulfone-based solvents are organic solvents that contain a sulfonyl group -S(=O)2- in their structure. Specific examples of sulfone solvents include sulfolane.

[0022] <Hydrocarbon solvents> The hydrocarbon solvent is a hydrocarbon solvent that is composed of an optionally halogenated hydrocarbon and has no substituents other than halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, with fluorine atoms being preferred. Specific examples of hydrocarbon solvents include n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, and n-hexadecane.

[0023] The two or more solvents in the membrane cleaning solution of the present embodiment are preferably a mixed solvent of two or more solvents selected from the group consisting of ketone-based solvents, ester-based solvents, alcohol-based solvents, and ether-based solvents, among the above. In this specification, the two or more solvents may be those containing two types of compounds and may be two or more solvents of the same classification, i.e., the two or more solvents may be a mixed solvent of 1-octanone and cyclohexanone, both of which are classified as ketone solvents.

[0024] <Metal remover> Specific examples of the metal remover in the membrane cleaning solution of this embodiment include metal chelating agents and organic acids.

[0025] <Metal chelating agents> Specific examples of the metal chelating agent in the membrane cleaning solution of the present embodiment include aminocarboxylic acid chelating agents such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, and diethylenetriaminepentaacetic acid; phosphonic acid chelating agents such as 1-hydroxyethane-1,1-diphosphonic acid and nitrilotris(methylenephosphonic acid); and compound (A1) represented by the following general formula (a-1) (hereinafter, also simply referred to as "compound (A1)"). Among the above, the metal chelating agent in this embodiment is preferably a compound (A1) represented by the following general formula (a-1).

[0026] ·Compound (A1) The compound (A1) in the membrane cleaning solution of this embodiment is a compound represented by the following general formula (a-1).

[0027] [ka] [In the formula, Ra 1 and Ra 2 are each independently an alkyl group having 1 to 3 carbon atoms. 3 and Ra 4 are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. 1 and Ya 2 are each independently a single bond, -O-, -S- or -N(Ra 5 )-. Ra 5 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 0 to 3.

[0028] In the formula (a-1), Ra 1 ~Ra 5 Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. In the formula (a-1), Ra 1 and Ra 2 are each independently preferably a methyl group or an ethyl group, more preferably a methyl group. Ra 3 and Ra 4 are each preferably a hydrogen atom. Ya 1 is preferably a single bond or —O—, more preferably a single bond. Ya 2 is preferably a single bond or —O—, more preferably a single bond. n is preferably 1 or 2, and more preferably 1.

[0029] Of the above, acetylacetone (AcAc) is preferred as the compound (A1).

[0030] The metal chelating agents may be used alone or in combination of two or more.

[0031] ≪Organic acid≫ Examples of organic acids in the membrane cleaning solution of this embodiment include carboxylic acids such as lactic acid (LA), citric acid, malic acid, formic acid, acetic acid, oxalic acid, 2-nitrophenylacetic acid, 2-ethylhexanoic acid, and dodecanoic acid; sugar acids such as ascorbic acid and glucuronic acid; sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid; and phosphoric acid and phosphate esters such as bis(2-ethylhexyl)phosphate.

[0032] Of the above, the organic acid in the membrane cleaning solution of this embodiment is preferably a carboxylic acid, more preferably a hydroxy acid such as lactic acid, citric acid, or malic acid, and even more preferably lactic acid.

[0033] The organic acids may be used alone or in combination of two or more.

[0034] The membrane cleaning solution of the present embodiment preferably contains two or more types of metal removers. More specifically, the membrane cleaning solution of the present embodiment preferably contains two or more metal removers selected from the group consisting of the above-mentioned metal chelating agents and organic acids, more preferably contains two or more metal removers selected from the group consisting of the above-mentioned compound (A1) and organic acids, and even more preferably contains two or more metal removers selected from the group consisting of the above-mentioned compound (A1) and carboxylic acids.

[0035] The membrane cleaning solution of the present embodiment preferably contains, among the above, the metal chelating agent and the organic acid described above, more preferably contains the compound (A1) and the organic acid described above, and further preferably contains the compound (A1) and the carboxylic acid described above.

[0036] The membrane cleaning solution of the present embodiment may contain optional components other than the above-mentioned solvent and metal remover, as long as the effects of the present invention are not impaired. Examples of the optional components include a pH adjuster and a surfactant.

[0037] [Hansen solubility parameters of membrane cleaning solution] The membrane cleaning solution of this embodiment contains the above-mentioned two or more solvents and a metal remover, and the distance between the Hansen solubility parameter of the membrane cleaning solution and the Hansen solubility parameter of dimethylacetamide is 1.0 or less.

[0038] The membrane cleaning solution of the present embodiment has a distance (HSP distance) between the Hansen solubility parameter of the membrane cleaning solution of the present embodiment and the Hansen solubility parameter of dimethylacetamide of 1.0 or less, preferably 0.8 or less, and more preferably 0.5 or less.

[0039] The membrane cleaning solution of this embodiment can remove both organic residues and metal impurities more effectively regardless of the membrane material, provided that the HSP distance of the membrane cleaning solution of this embodiment is equal to or less than the above-mentioned preferred value.

[0040] Here, the "Hansen solubility parameter" is a theoretically calculated numerical constant that is a useful tool for predicting the ability of a solvent material to dissolve a particular solute. Hansen solubility parameters are the following three experimentally and theoretically derived Hansen solubility parameters (δ d (dispersion force term), δ p (polar term) and δ h The Hansen solubility parameter (HSP) is a measure of the overall strength and selectivity of a material. The unit of the Hansen solubility parameter is MPa. 0.5 or (J / cc) 0.5 It is granted at. δ d : Energy derived from intermolecular dispersion forces δ p : Energy derived from intermolecular polar forces δ h : Energy derived from hydrogen bonding forces between molecules

[0041] "Hansen solubility parameters" can be calculated, for example, by "Molecular Modeling Pro" software, version 5.1.9 (ChemSW, Fairfield Calif., www.chemsw.com) or Hansen Solubility from Dynacomp Software.

[0042] Since the membrane cleaning solution of this embodiment is a mixture, the Hansen solubility parameter of the membrane cleaning solution of this embodiment can be determined as follows. For example, solvent S 1 (δ ds1 , δ ps1 , δ hs1 ), solvent S 2 (δ ds2 , δ ps2 , δ hs2 ), Metal Remover B 1 (δ dB1 , δ pB1 , δ hB1 ), and Metal Remover B 2 (δ dB2 , δ pB2 , δ hB2 ) a membrane cleaning solution CS consisting of solvent S 1 The amount of the compounded solvent is a, and the solvent S 2 The compounding amount of b, metal remover B 1 The compounding amount of c and metal remover B 2 When the blending amount of is d, the δ of the membrane cleaning solution CS dcs (dispersion force term), δ pcs (polar term) and δ hcs (Hydrogen bond term) is calculated using the following formula, where a+b+c+d=100. δ dcs =(δ ds1 ×a+δ ds2 ×b+δ dB1 ×c+δ dB2 ×d) / 100 δ pcs =(δ ps1 ×a+δ ps2 ×b+δ pB1 ×c+δ pB2 ×d) / 100 δ hcs =(δ hs1 ×a+δ hs2 ×b+δ hB1 ×c+δ hB2 ×d) / 100

[0043] The distance (HSP distance) between the Hansen solubility parameter of the membrane cleaning solution CS (membrane cleaning solution of this embodiment) and the Hansen solubility parameter of dimethylacetamide is calculated by the following formula (1). HSP distance={4(δ dcs -δ dDMAc ) 2 +(δ pcs -δ pDMAc ) 2 +(δ hcs -δ hDMAc ) 2} 0.5 ···(1) In addition, the dispersion force term of dimethylacetamide (δ dDMAc ) is 16.8, and the polar term (δ pDMAc ) is 11.5, and the hydrogen bond term (δ hDMAc ) uses the value 9.4.

[0044] The HSP distance in the membrane cleaning solution of this embodiment is, for example, the dispersion force term (δ dDMAc ), polarity term (δ pDMAc ), and the hydrogen bond term (δ hDMAc ) can be controlled by employing a solvent or metal removal agent close to the value of the respective components.

[0045] <First membrane cleaning solution> The membrane cleaning solution of the first embodiment contains a mixed solvent of two or more solvents selected from the group consisting of ketone-based solvents, ester-based solvents, alcohol-based solvents, and ether-based solvents, and a metal-removing agent.

[0046] The mixed solvent is more preferably a mixed solvent of one or more solvents selected from the group consisting of ketone solvents and ester solvents (hereinafter also referred to as "solvent S1") and one or more solvents selected from the group consisting of alcohol solvents and ether solvents (hereinafter also referred to as "solvent S2"), even more preferably a mixed solvent of an ester solvent and an ether solvent, and particularly preferably a mixed solvent of a lactone solvent and an ether solvent.

[0047] For example, when the two or more solvents in the membrane cleaning solution of this embodiment are a mixed solvent of solvent S1 and solvent S2, the mixing ratio of solvent S1 to solvent S2 (solvent S1:solvent S2) is preferably 20:80 to 80:20 by mass, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40.

[0048] Suitable combinations of two or more solvents in the membrane cleaning solution of this embodiment include a mixed solvent of one or more solvents selected from the group consisting of γ-butyrolactone, ε-caprolactone, and γ-valerolactone with one or more solvents selected from the group consisting of EGME, PGME, and PGEE; a mixed solvent of dihydrolevoglucosenone (silene) and PG; and the like. Among these, the solvent is preferably a mixed solvent of one or more solvents selected from the group consisting of γ-butyrolactone, ε-caprolactone, and γ-valerolactone, and one or more solvents selected from the group consisting of EGME, PGME, and PGEE, and more preferably a mixed solvent of γ-butyrolactone and PGME.

[0049] Specific examples of the metal remover in the membrane cleaning solution of the present embodiment include metal chelating agents and organic acids, and any one of these may be used alone or two or more of them may be used in combination.

[0050] The contents of the mixed solvent and the metal remover in the membrane cleaning solution of this embodiment are appropriately selected so that the above-mentioned HSP distance is 1.0 or less. The content of the mixed solvent in the membrane cleaning liquid of this embodiment is preferably 90 to 99.5 mass %, more preferably 95 to 99 mass %, relative to 100 mass % of the total amount of the membrane cleaning liquid. Furthermore, the content of the metal remover in the membrane cleaning solution of this embodiment is preferably 0.1 to 10 mass%, more preferably 0.5 to 10 mass%, even more preferably 0.5 to 5 mass%, and particularly preferably 1 to 5 mass%, relative to 100 mass% of the total amount of the membrane cleaning solution.

[0051] <Second membrane cleaning solution> The membrane cleaning solution of the second embodiment contains a mixed solvent of two or more solvents selected from the group consisting of ketone-based solvents, ester-based solvents, alcohol-based solvents, and ether-based solvents, the metal chelating agent described above, and the organic acid described above.

[0052] Suitable combinations of two or more solvents in the membrane cleaning liquid of this embodiment are the same as the suitable combinations of two or more solvents in the membrane cleaning liquid of the first embodiment described above.

[0053] The metal chelating agent in the membrane cleaning solution of this embodiment is preferably the compound (A1), and more preferably acetylacetone (AcAc).

[0054] The organic acid in the membrane cleaning solution of this embodiment is preferably a carboxylic acid, more preferably a hydroxy acid such as lactic acid, citric acid, or malic acid, and even more preferably lactic acid.

[0055] The contents of the mixed solvent, metal chelating agent, and organic acid are appropriately selected so that the above-mentioned HSP distance is 1.0 or less. The content of the mixed solvent in the membrane cleaning liquid of this embodiment is preferably 90 to 99.5 mass %, more preferably 95 to 99 mass %, relative to 100 mass % of the total amount of the membrane cleaning liquid.

[0056] The content of the metal chelating agent in the membrane cleaning solution of this embodiment is preferably 0.1 to 9 mass %, more preferably 0.5 to 9 mass %, and even more preferably 0.5 to 5 mass %, based on the total amount of the membrane cleaning solution.

[0057] The proportion of the compound (A1) in the metal chelating agent is preferably 50% by mass or more, more preferably 75% by mass or more, and may be 100% by mass, based on the total mass of the metal chelating agent.

[0058] The content of the organic acid in the membrane cleaning solution of this embodiment is preferably 0.1 to 9 mass %, more preferably 0.5 to 9 mass %, and even more preferably 0.5 to 5 mass %, relative to 100 mass % of the total amount of the membrane cleaning solution.

[0059] The proportion of carboxylic acid in the organic acid is preferably 50% by mass or more, more preferably 75% by mass or more, and may be 100% by mass, based on the total mass of the organic acid.

[0060] The membrane cleaning solution of the first embodiment and the membrane cleaning solution of the second embodiment may further contain the above-mentioned optional line segment as necessary.

[0061] The membrane cleaning solution of this embodiment is a cleaning solution that is useful for cleaning membranes. The form and shape of the membrane are not particularly limited, and examples thereof include flat membranes, hollow fiber membranes, tubular membranes, spiral membranes, thin films, and the like. The material of the membrane is not particularly limited, and examples thereof include polyolefins (polyethylene, polypropylene, etc.), polysulfones, polyacrylonitrile, polyamides, polyimides, polyvinyl alcohols, cellulose acetates, fluoropolymers, and ceramics. The membrane cleaning solution of this embodiment is a cleaning solution particularly useful for cleaning membranes containing polyolefin (particularly, polyethylene) and polyimide. That is, the membrane cleaning solution of this embodiment is preferably a polyolefin resin membrane cleaning solution (particularly, a polyethylene resin membrane cleaning solution) or a polyimide resin membrane cleaning solution. Here, the polyimide resin membrane means a membrane containing one or more resins selected from the group consisting of polyamic acid and polyimide.

[0062] The membrane cleaning solution of the present embodiment described above contains two or more solvents and a metal remover, and the distance between the Hansen solubility parameter of the membrane cleaning solution and the Hansen solubility parameter of dimethylacetamide is 1.0 or less. The membrane cleaning solution of this embodiment has a Hansen solubility parameter adjusted to be close to that of DMAc, which is generally used for cleaning polyimide membranes, and therefore has good cleaning properties for polyimide membranes. Furthermore, although the reason is unclear, the membrane cleaning solution of this embodiment has an excellent cleaning ability for non-polar polyethylene-based membranes, which have properties significantly different from those of polar polyimide-based membranes, by adjusting the Hansen solubility parameter of the entire membrane cleaning solution to approach that of DMAc and by containing a metal remover. In addition, the presence of a metal remover provides excellent removal of metal impurities. Therefore, the membrane cleaning solution of this embodiment can remove both organic residues and metal impurities regardless of the membrane material, such as polyimide-based membranes or polyethylene-based membranes whose properties are significantly different from polyimide-based membranes.

[0063] (Membrane cleaning method) The membrane cleaning method of this embodiment is a membrane cleaning method in which the membrane is cleaned by bringing the above-mentioned membrane cleaning solution into contact with the membrane. The membrane may be the same as the membrane described above in relation to the membrane cleaning solution.

[0064] More specifically, examples of the cleaning process for cleaning the membrane by bringing the above-mentioned membrane cleaning solution into contact with the membrane include a method of immersing the membrane in the above-mentioned membrane cleaning solution and a method of spraying the above-mentioned membrane cleaning solution onto the membrane. The washing step may be carried out only once or may be carried out multiple times. In the washing step, the above-mentioned membrane washing solution may be heated, or washing may be carried out at room temperature (for example, 23° C.).

[0065] The membrane cleaning method of this embodiment may include a drying step of drying the membrane cleaned in the above-mentioned cleaning step. Specific examples of the drying step include air drying at room temperature, placing the cleaned membrane in a thermostatic chamber and heating it, and vacuum drying, and other known methods can be applied without limitation.

[0066] According to the membrane cleaning method of the present embodiment described above, the above-mentioned membrane cleaning solution is used, so that both organic residues and metal impurities can be easily removed regardless of the membrane material.

[0067] Furthermore, the membrane cleaning method of the present embodiment may include a step of cleaning the membrane by bringing the membrane into contact with a membrane cleaning solution different from the membrane cleaning solution (hereinafter also referred to as "cleaning step B") before or after a step of cleaning the membrane by bringing the above-mentioned membrane cleaning solution into contact with the membrane (hereinafter also referred to as "cleaning step A"). That is, the method for cleaning a membrane of this embodiment may include (i) a step of cleaning the membrane by bringing a membrane cleaning liquid different from the above-mentioned membrane cleaning liquid into contact with the membrane, and a step of cleaning the membrane by bringing the cleaned membrane into contact with the above-mentioned membrane cleaning liquid; (ii) a step of cleaning the membrane by bringing the above-mentioned membrane cleaning liquid into contact with the membrane, and a step of cleaning the membrane by bringing the cleaned membrane into contact with a membrane cleaning liquid different from the above-mentioned membrane cleaning liquid; or (iii) a step of cleaning the membrane by bringing a membrane cleaning liquid different from the above-mentioned membrane cleaning liquid into contact with the membrane, and a step of cleaning the membrane by contacting the cleaned membrane with the above-mentioned membrane cleaning liquid; and a further step of cleaning the membrane by bringing the cleaned membrane into contact with a membrane cleaning liquid different from the above-mentioned membrane cleaning liquid into contact with the membrane. In (iii), the membrane cleaning liquids different from the membrane cleaning liquid described above in the cleaning steps before and after the step of cleaning the membrane by bringing the membrane into contact with the membrane may be the same or different.

[0068] Cleaning process B Examples of a method for cleaning the membrane by bringing a membrane cleaning liquid different from the membrane cleaning liquid described above in the cleaning step B into contact with the membrane include the same method as the method described in the cleaning step A. The washing step B may be carried out only once or multiple times before or after the washing step A.

[0069] -Membrane cleaning solution different from the above-mentioned membrane cleaning solution A membrane cleaning solution (hereinafter also referred to as "membrane cleaning solution B") different from the above-mentioned membrane cleaning solution in cleaning step B of the membrane cleaning method of this embodiment specifically includes a membrane cleaning solution containing a solvent but not containing a gold removing agent. Furthermore, a typical example of membrane cleaning solution B is a membrane cleaning solution consisting of only a solvent.

[0070] Membrane cleaning solution B Specific examples of the solvent in the membrane cleaning solution B include polar solvents such as ketone-based solvents, ester-based solvents, alcohol-based solvents, nitrile-based solvents, amide-based solvents, ether-based solvents, sulfoxide-based solvents, and sulfone-based solvents; and non-polar solvents such as hydrocarbon-based solvents. Specific examples of the solvent include the same solvents as those in the membrane cleaning solution described above.

[0071] Among the above, the membrane cleaning solution B preferably contains an alcohol-based solvent, more preferably contains an alcohol-based solvent having 1 to 5 carbon atoms, and further preferably contains 2-propanol (isopropyl alcohol). That is, one embodiment is a membrane cleaning method comprising: a step of cleaning the membrane by bringing the above-mentioned membrane cleaning solution into contact with the membrane; and a step of cleaning the membrane by bringing the membrane into contact with an alcohol-based solvent (preferably, 2-propanol) before or after the step of cleaning the membrane by bringing the above-mentioned membrane cleaning solution into contact with the membrane.

[0072] The membrane cleaning method of this embodiment may include a drying step of drying the membrane cleaned in the above-mentioned cleaning step A or cleaning step B. Specific examples of the drying step that can be applied include known methods such as air drying at room temperature, placing the cleaned membrane in a thermostatic chamber and heating it, and vacuum drying, without any limitations.

[0073] The membrane cleaning method of the present embodiment described above is a membrane cleaning method that includes the cleaning step B in addition to the cleaning step A described above, and therefore can remove more organic residues and metal impurities attached to the membrane than the membrane cleaning method that includes only the cleaning step A described above. [Example]

[0074] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0075] (Preparation of membrane cleaning solution) The components were mixed in the composition ratios shown in Table 1 to obtain the membrane cleaning solutions of each example. The abbreviations in the table represent the following compounds. n-BA: n-butanol PGME: Propylene glycol monomethyl ether PGMEA: Propylene glycol monomethyl ether acetate DMAc: dimethylacetamide DMSO: dimethyl sulfoxide CH: Cyclohexanone GBL: gamma-butyrolactone LA: Lactic acid AcAc: acetylacetone

[0076] The values ​​in parentheses in Table 1 are the blending amounts (mass %).

[0077] [Table 1]

[0078] [Calculating HSP distance] Example 1 The Hansen solubility parameters of each component of the membrane cleaning solution in Example 1 were calculated using "Molecular Modeling Pro" software, version 5.1.9 (ChemSW, Fairfield, CA, www.chemsw.com). The Hansen solubility parameters of each component are shown below.

[0079] GBL dispersion force term (δ dGBL ) is 18, and the polar term (δ pGBL ) is 16.6, and the hydrogen bond term (δ hGBL ) was set to a value of 7.4. PGME dispersion term (δ dPGME ) is 15.6, and the polar term (δ pPGME ) is 6.3, and the hydrogen bond term (δ hPGME ) used a value of 11.6. Dispersion force term of LA (δ dLA ) is 17, and the polar term (δ pLA ) is 8.3, and the hydrogen bond term (δ hLA ) used a value of 28.4. Dispersion force term of AcAc (δ dAcAc ) is 16.1, and the polar term (δ pAcAc ) is 10, and the hydrogen bond term (δ hAcAc ) used a value of 6.2.

[0080] The dispersion force term (δ dt ), polarity term (δ pt ), and the hydrogen bond term (δ ht ) was calculated as follows: δ dt =(δ dGBL ×47.04+δ dPGME ×50.96+δ dLA ×1+δ dAcAc ×1) / 100 δ pt =(δ pGBL ×47.04+δ pPGME ×50.96+δ pLA ×1+δ pAcAc ×1)) / 100 δ ht =(δ hGBL ×47.04+δ hPGME ×50.96+δ hLA ×1+δ hAcAc ×1) / 100

[0081] In addition, the distance (HSP distance) between the Hansen solubility parameter of the membrane cleaning solution in Example 1 and the Hansen solubility parameter of dimethylacetamide was calculated by the following formula (1t). HSP distance={4(δ dt -δ dDMAc ) 2 +(δ pt -δ pDMAc ) 2 +(δ ht -δ hDMAc )2} 0.5 ···(1t) In addition, the dispersion force term of dimethylacetamide (δ dDMAc ) is 16.8, and the polar term (δ pDMAc ) is 11.5, and the hydrogen bond term (δ hDMAc ) used a value of 9.4.

[0082] (Comparative Examples 1 to 7) Using the same method as in Example 1 above, the Hansen solubility parameters of the membrane cleaning solutions of Comparative Examples 1 to 7 and the distance between the Hansen solubility parameters of the membrane cleaning solutions of Comparative Examples 1 to 7 and the Hansen solubility parameter of dimethylacetamide were determined.

[0083] Table 2 shows the Hansen solubility parameters of the membrane cleaning solutions in each example, and the distance (HSP distance) between the Hansen solubility parameters of the membrane cleaning solutions in each example and the Hansen solubility parameter of dimethylacetamide.

[0084] [Evaluation of membrane cleaning ability] The membrane cleaning ability of each membrane cleaning solution was evaluated by measuring the non-volatile residue (NVR) of a polyimide-based porous membrane (PI film) and a polyethylene-based porous membrane (PE film) after cleaning with each membrane cleaning solution. The smaller the mass of non-volatile residue (NVR), the higher the cleaning ability of the membrane cleaning solution for organic residues. The specific steps are as follows:

[0085] Cleaning of PI film A PI film was produced by the method described in "<Reference Example> Formation of Porous Polyimide Film" in JP 2017-202479 A. The PI film (600 cm 2 The PI film was immersed in 800 g of each membrane cleaning solution, stirred, and then removed. This procedure was repeated three times. 3 Then, isopropyl alcohol was added to the sample at a rate of 100 cm 3 It was heated until it evaporated. 3The evaporated isopropyl alcohol was transferred to a platinum dish that had been weighed in advance on an electronic balance, and heated until the isopropyl alcohol was completely evaporated. After the evaporation process, the platinum dish was weighed, and the mass of the non-volatile residue (NVR) was measured from the weight difference with the pre-weighed platinum dish. The results were expressed as "PI NVR (mg / 600 cm)." 2 )" in Table 2.

[0086] Cleaning of PE film PE film (Teijin, product name: Miraim, 600cm) 2 The mass of non-volatile residue (NVR) was measured in the same manner as in the above-mentioned PI film cleaning, except that PE NVR (mg / 600 cm) was used. The results are reported as "PE NVR (mg / 600 cm)." 2 )" in Table 2.

[0087] About Reference Example 1 As Reference Example 1, the PI film and the PE film were washed in the same manner as the above-mentioned PI film washing and PE film washing, respectively, without washing them with the membrane washing solution, and the "PI NVR (mg / 600 cm 2 ) and PE NVR (mg / 600cm 2 The results are shown in Table 2.

[0088] [Table 2]

[0089] As shown in Table 2, the membrane cleaning solution of the example had a higher PI NVR (mg / 600cm) than the membrane cleaning solution of the comparative example. 2 ) and PE NVR (mg / 600cm 2 )" values ​​were all low. From this, it was confirmed that the membrane cleaning solution of the example can remove organic residues regardless of the membrane material.

[0090] [Evaluation of calcium removal] PI films were prepared using the method described in "<Reference Example> Formation of Porous Polyimide Film" in JP 2017-202479 A. The PI films were immersed in the membrane cleaning solutions of each example (Example 1, Comparative Examples 1-3, and 5-7), and the amount of calcium before and after immersion was measured using an inductively coupled plasma mass spectrometer (Agilent Technologies, product name: ICP-MS 8900). The higher the amount of calcium, the higher the calcium removal ability of the membrane cleaning solution. The specific steps are as follows:

[0091] 30 g of each membrane cleaning solution was prepared, and the amount of calcium in each membrane cleaning solution (before immersion in the PI film) was measured using the inductively coupled plasma mass spectrometer.

[0092] Next, the PI film was immersed in 800 g of each of the membrane cleaning solutions of the above examples for one day. Next, each PI film was taken out, and the amount of calcium in the membrane cleaning solution of each example was measured in the same manner as above.

[0093] The calcium content in the membrane cleaning solution before the PI film was removed from the calcium content in the membrane cleaning solution after the PI film was removed was calculated as the "calcium content (ppb)" and is shown in Table 3.

[0094] About Reference Example 2 In Reference Example 2, the "calcium content (ppb)" was measured in the same manner as above, except that hydrochloric acid (10% HCl) was used. The results are shown in Table 3.

[0095] About Reference Example 3 In Reference Example 3, the "calcium amount (ppb)" was measured in the same manner as above, except that isopropyl alcohol (IPA) was used. The results are shown in Table 3.

[0096] [Table 3]

[0097] As shown in Table 3, the membrane cleaning solution of the example contains a larger amount of calcium than the membrane cleaning solution of the comparative example, and it was confirmed that more calcium attached to the PI film can be absorbed into the membrane cleaning solution, i.e., it can be removed from the PI film. It was also confirmed that the membrane cleaning solution of the example was superior in removing calcium to hydrochloric acid, which is generally used as a membrane metal remover.

[0098] <Evaluation of metal removal ability> A PI film was produced by the method described in "<Reference Example> Formation of Porous Polyimide Film" in JP 2017-202479 A. The PI film was cleaned using the membrane cleaning solution of Example 1 described above, and the metal removability of the cleaned PI film was evaluated. The specific steps are as follows:

[0099] [Metal Extraction Measurement (1)] 0.1m of PI film 2 100 cm of the membrane cleaning solution of Example 1 3 The membrane was then immersed in the solution at room temperature (23°C) for one day. Then, the membrane cleaning solution was completely removed, and the solvent was replaced twice with OK73 thinner (manufactured by Tokyo Ohka Kogyo Co., Ltd.). After that, the membrane was immersed in 100 cm 3 The PI film was immersed in OK73 thinner for one day at room temperature. The PI film was then removed, and the metal content of the OK73 thinner was measured using an inductively coupled plasma mass spectrometer (Agilent Technologies, product name: ICP-MS 8900). The metals measured were Li, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, As, Sr, Zr, Mo, Ag, Cd, Sn, Sb, Ba, W, Au, and Pb. The process of contacting the PI film with OK73 thinner is necessary for measuring the amount of metal extraction, but is not intended to clean the PI film. As a blank, 0.1 mm of the PI film was not washed with the membrane cleaning solution. 2 After washing the film twice with OK73 thinner (Tokyo Ohka Kogyo Co., Ltd.), the PI film was soaked in 100 cm 3The metal content was also measured after immersion in the solution at room temperature for one day. In this case, the smaller the measured metal amount compared to the metal amount of the blank, the smaller the amount of metal remaining in the film, which means that the metal removal efficiency is higher. Among these results, the calcium content and total metal content are shown in Table 4.

[0100] [Table 4]

[0101] As shown in Table 4, the membrane cleaning solution of the example had a small total amount of calcium and metals, and it was confirmed that it was able to remove more metals adhering to the PI film.

[0102] [Metal Extraction Measurement (2)] The metal removal ability was evaluated for a membrane cleaning method that included a step of cleaning the PI film with the membrane cleaning solution of Example 1 described above, as well as a step of cleaning with isopropyl alcohol. The specific steps are as follows:

[0103] Evaluation of metal removal performance of membrane cleaning method X The membrane cleaning method X includes a step of cleaning a PI film with the membrane cleaning solution of Example 1, and a step of further cleaning the PI film that has been cleaned with the membrane cleaning solution of Example 1 with isopropyl alcohol. Specifically, 0.1 m of the PI film 2 100 cm of the membrane cleaning solution of Example 1 3 The membrane was then immersed in the cleaning solution of Example 1 at room temperature (23°C) for one day. 3 The process of immersing the sample in water, stirring, and removing it was repeated four times. Then, all the isopropyl alcohol was removed, and the sample was placed in 100 cm of OK73 thinner. 3 The PI film was then removed and the amount of metal in the OK73 thinner was measured in the same manner as in [Measurement of the amount of extracted metal (1)] above. The results of the calcium content and total metal content are shown in Table 5 under "Membrane Cleaning Method X."

[0104] Evaluation of metal removal ability of membrane cleaning method Y Membrane cleaning method Y includes a step of cleaning a PI film with isopropyl alcohol, a step of further cleaning the PI film cleaned with isopropyl alcohol with the membrane cleaning solution of Example 1, and a step of further cleaning the PI film cleaned with the membrane cleaning solution of Example 1 with isopropyl alcohol. Specifically, 0.1 m of the PI film 2 100cm of isopropyl alcohol 3 The PI film was then immersed in 100 cm of the membrane cleaning solution of Example 1, stirred, and removed, and this procedure was repeated four times. 3 The membrane was then immersed in the cleaning solution of Example 1 at room temperature (23°C) for one day. 3 The process of immersing the sample in water, stirring, and removing it was repeated four times. Then, all the isopropyl alcohol was removed, and the sample was placed in 100 cm of OK73 thinner. 3 The PI film was then removed and the amount of metal in the OK73 thinner was measured in the same manner as in [Measurement of the amount of extracted metal (1)] above. The results of the calcium content and total metal content are shown in Table 5 under "Membrane cleaning method Y."

[0105] [Table 5]

[0106] As shown in Tables 4 and 5, in the membrane cleaning method using the membrane cleaning solution of Example 1, it was confirmed that by further including a step of cleaning the PI film with isopropyl alcohol before, before, or after the membrane cleaning step using the membrane cleaning solution of Example 1, metals adhering to the PI film can be further removed.

[0107] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Addition, omission, substitution, and other modifications of the configuration are possible within the scope of the spirit of the present invention. The present invention is not limited by the above description, but is limited only by the scope of the appended claims.

Claims

1. A membrane cleaning solution containing a solvent and a metal removing agent, containing two or more solvents, The distance between the Hansen solubility parameter of the membrane cleaning solution and the Hansen solubility parameter of dimethylacetamide is 1.0 or less; the solvent is two or more solvents selected from the group consisting of ketone-based solvents, ester-based solvents, alcohol-based solvents, nitrile-based solvents, ether-based solvents, sulfoxide-based solvents, sulfone-based solvents, and hydrocarbon-based solvents; the total content of the two or more solvents is 90 to 99.5% by mass with respect to 100% by mass of the total amount of the membrane cleaning solution, The membrane cleaning solution, wherein the content of the metal remover is 0.1 to 10 mass % relative to 100 mass % of the total amount of the membrane cleaning solution.

2. The membrane cleaning solution described in claim 1, wherein the solvent is two or more solvents selected from the group consisting of ketone-based solvents, ester-based solvents, alcohol-based solvents, and ether-based solvents.

3. The membrane cleaning solution according to claim 1 or 2, comprising two or more types of the metal remover.

4. The membrane cleaning solution according to any one of claims 1 to 3, wherein the metal remover comprises a compound (A1) represented by the following general formula (a-1): 【Chemistry 1】 [In the formula, Ra １ and Ra ２ are each independently an alkyl group having 1 to 3 carbon atoms. ３ and Ra ４ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. １ and Ya ２ are each independently a single bond, —O—, —S— or —N(Ra ５ )-. Ra ５ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is an integer of 0 to 3.

5. The membrane cleaning solution according to any one of claims 1 to 4, wherein the metal remover comprises an organic acid.

6. The membrane cleaning solution according to claim 5 , wherein the organic acid is a carboxylic acid.

7. A method for cleaning a membrane, comprising contacting the membrane with the membrane cleaning solution according to any one of claims 1 to 6 to clean the membrane.

8. The method for cleaning a membrane according to claim 7 , wherein the membrane contains polyimide or polyethylene.

9. The membrane cleaning method according to claim 7, comprising a step of cleaning the membrane by contacting the membrane with a membrane cleaning solution different from the membrane cleaning solution according to any one of claims 1 to 6 before or after the step of cleaning the membrane by contacting the membrane with the membrane cleaning solution.

10. The method for cleaning a membrane according to claim 9 , wherein the membrane cleaning solution different from the membrane cleaning solution contains an alcohol-based solvent.

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