Semipermeable membrane treatment method, semipermeable membrane production method, and semipermeable membrane element production method

Abstract

To provide a treatment method having simplicity and long-lasting effectiveness, enabling improvement of the removal rate of a semipermeable membrane not reaching a desired removal performance or having decreased removal performance.SOLUTION: A semipermeable membrane treatment method comprising a step of bringing a semipermeable membrane having a separation functional layer comprising polyamide into contact with a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensation agent.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for treating and producing a semipermeable membrane having a separating functional layer containing a polyamide, and a method for producing a semipermeable membrane element. [Background technology]

[0002] Semipermeable membranes used for separating liquid mixtures include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes are used, for example, in producing drinking water from water containing salt or harmful substances, producing industrial ultrapure water, treating wastewater, or recovering valuable resources.

[0003] The majority of currently commercially available reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes. A typical composite semipermeable membrane is a polyamide semipermeable membrane having a microporous support membrane and a separation functional layer covering the microporous support membrane, the separation functional layer being made of a crosslinked aromatic polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide, and having high water permeability and selective separation properties.

[0004] However, during use, the semipermeable membrane's permeability can be reduced by organic fouling, inorganic fouling (scaling), biofouling, and other factors caused by organic substances, inorganic substances, and microorganisms present in the liquid mixture. To restore the permeability of a semipermeable membrane that has been reduced by fouling, it is cleaned with chemicals containing acids and alkalis. Furthermore, oxidizing agents such as chlorine are sometimes supplied to clean pipes, and if these oxidizing agents are mixed into the liquid supplied to the semipermeable membrane, they may come into contact with the semipermeable membrane. Even if the substances that cause fouling are removed by cleaning with acids or alkalis, restoring the permeability of the semipermeable membrane, the semipermeable membrane may be deteriorated and its removal performance may be reduced as a result of contact with chemicals such as oxidizing agents.

[0005] Patent Document 1 discloses a method for regenerating a reverse osmosis membrane of a reverse osmosis membrane element with deteriorated performance, by carrying out the following steps: (i) removing the active layer of the composite reverse osmosis membrane; (ii) treating the support membrane surface from which the active layer has been removed with a polyfunctional amine solution to retain the polyfunctional amine on the support membrane surface; and (iii) treating the membrane surface with a non-aqueous organic solution containing a polyfunctional acid halide to form an active layer.

[0006] Patent Document 2 cites that degradation of polyamide membranes by oxidizing agents is caused by the cleavage of C-N bonds (amide bonds), which leads to the collapse of the sieving structure. It also discloses a method for improving rejection, which includes passing a first organic compound with a molecular weight of less than 200, a second organic compound with a molecular weight of 200 to less than 500, and a third organic compound with a molecular weight of 500 or more through a polyamide membrane. Patent Document 2 states that the low-molecular-weight first and second organic compounds are highly soluble in water and react with the carboxyl groups of the membrane to bond to the reverse osmosis membrane, forming an insoluble salt that plugs holes caused by membrane degradation, while the third organic compound plugs areas of severe degradation in the membrane, thereby increasing the membrane's rejection. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-156168 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-187469 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method of Patent Document 1, although an attempt is made to remove the active layer using a cleaning agent in step (i), there is a possibility that the active layer may not be sufficiently removed. In such a case, the support layer becomes non-uniform, and the polyamide remaining on the support layer may prevent the desired removal performance from being obtained even in subsequent steps (ii) and (iii). Furthermore, including the drying step of the composite reverse osmosis membrane element, at least four steps are required, making the operation complicated.

[0009] Furthermore, it is known that simply dissolving an organic compound having an amino group and an organic compound having a carboxy group, or an organic compound having both an amino group and a carboxy group, in water at room temperature generally does not produce an amide bond, and even if it does form, the reaction rate is 0.1% or less. In other words, the bonds formed between each organic compound and polyamide in the treatment method described in Patent Document 2 are non-covalent bonds such as hydrogen bonds and van der Waals forces, and these bonds are easily dissociated by changes in temperature or pH, causing the organic compound to be removed from the deteriorated area, potentially restoring the performance to that before the rejection improvement method was implemented.

[0010] Therefore, the present invention aims to provide a simple and highly effective treatment method that can improve the removal rate of semipermeable membranes that do not achieve the desired removal performance or have reduced removal performance. [Means for solving the problem]

[0011] In order to solve the above problems, the semipermeable membrane treatment method, the manufacturing method and treatment device for a semipermeable membrane element, and the liquid treatment method and fluid treatment device using a semipermeable membrane element of the present invention include the following configurations. [1] A method for treating a semipermeable membrane, comprising a step of contacting a semipermeable membrane having a separating functional layer containing a polyamide with a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent. [2] The treatment method according to the above [1], wherein the ratio of the total number of carboxyl groups of the polyfunctional carboxylic acid to the total number of amino groups of the polyfunctional amine in the solution is 0.5 or more and 2.0 or less. [3] The treatment method according to [1] or [2] above, wherein the concentration of the condensing agent in the solution is 0.03% by mass or more and 0.3% by mass or less. [4] The treatment method according to any one of the above [1] to [3], wherein the total number of moles of the condensing agent relative to the total number of carboxy groups of the polyfunctional carboxylic acids in the solution is 0.5 or more and 1.5 or less. [5] The treatment method according to any one of the above [1] to [4], wherein the concentration of the polyfunctional amine in the solution is 0.001% by mass or more and 0.010% by mass or less. [6] The treatment method according to any one of the above [1] to [5], wherein the condensing agent is a carbodiimide-based condensing agent or a triazine-based condensing agent. [7] The method according to any one of the above [1] to [6], wherein the polyfunctional amine has a molecular weight of 50 or more and 200 or less. [8] The method according to any one of the above [1] to [7], wherein the polyfunctional carboxylic acid has a molecular weight of 150 or more and 300 or less. [9] The treatment method according to any one of the above [1] to [8], wherein the time for which the solution is brought into contact with the semipermeable membrane is from 10 minutes to 72 hours.

[10] The treatment method according to any one of [1] to [9] above, wherein the semipermeable membrane is incorporated into a semipermeable membrane element, and the treatment method is performed on the semipermeable membrane element that exhibits at least one of a salt permeability that is 10% or more higher than the initial value and a neutral molecule permeability that is 10% or more higher than the initial value.

[11] The treatment method according to any one of the above [1] to

[10] , which is carried out on a semipermeable membrane that has been contacted with at least one selected from the group consisting of an acid with a pH of 4 or less, an alkali with a pH of 10 or more, and an oxidizing agent.

[12] A method for producing a semipermeable membrane having a separating functional layer containing a polyamide, the method comprising the treatment method according to any one of [1] to

[11] above.

[13] A method for producing a semipermeable membrane element, comprising subjecting the semipermeable membrane incorporated in the semipermeable membrane element to the treatment method according to any one of the above [1] to

[11] . [Effects of the Invention]

[0012] According to the present invention, it is possible to improve the removal performance of a semipermeable membrane whose removal performance does not reach a desired level or whose removal performance has deteriorated. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in further detail below. In this specification, "mass" has the same meaning as "weight".

[0014] <Processing method> (1) Overview Below, we will explain a method for treating a semipermeable membrane, which includes a step of contacting a semipermeable membrane having a separation functional layer containing polyamide (hereinafter also referred to as a "polyamide-based semipermeable membrane") with a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent.

[0015] The treatment method of the present invention can improve the performance of a polyamide-based semipermeable membrane that does not achieve the desired removal performance or whose performance has deteriorated due to contact with a chemical solution.

[0016] The polyamide contained in the separation functional layer of the semipermeable membrane of the present invention can be hydrolyzed by contact with an oxidizing agent mixed in raw water supplied to the semipermeable membrane. The hydrolyzed portions become coarse pores, allowing the substances to be removed to pass through. Furthermore, in the coarse pores, carboxyl groups are exposed by the hydrolysis of the polyamide.

[0017] The large pores can be reduced by bonding the polyfunctional amine to functional groups such as carboxyl groups in the polyamide separation layer. Here, bonding refers to bonding by ionic bonds, covalent bonds, or intermolecular forces (van der Waals forces or hydrogen bonds).

[0018] Furthermore, the coarse pores can also be reduced by bonding a polyfunctional carboxylic acid to a functional group such as an amino group in the polyamide separating functional layer.

[0019] In the method for treating a semipermeable membrane of the present invention, at least one of a polyfunctional amine and a polyfunctional carboxylic acid is bonded to a polyamide to reduce the size of the coarse pores, thereby improving the performance of the semipermeable membrane. More specifically, an amide bond is formed between the polyfunctional amine and a terminal carboxyl group in the polyamide separating functional layer, or between the polyfunctional carboxylic acid and a terminal amino group in the polyamide separating functional layer.

[0020] Furthermore, the semipermeable membrane treatment method of the present invention uses a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent, and the polyfunctional amine and polyfunctional carboxylic acid themselves, or oligomers formed by the combination of the polyfunctional amine and polyfunctional carboxylic acid in the solution, are expected to reduce coarse pores of various sizes by binding to the terminal carboxy groups or terminal amino groups in the polyamide separation function layer, thereby enabling the efficient reduction of coarse pores with fewer steps.

[0021] (2) Solution contact process The method for treating a semipermeable membrane of the present invention includes a step of contacting a polyamide-based semipermeable membrane with a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent. Hereinafter, this step will also be referred to as a "solution contact step."

[0022] Examples of polyfunctional amines include polyfunctional aromatic amines and polyfunctional aliphatic amines.

[0023] The term "polyfunctional aromatic amine" refers to an aromatic amine having two or more primary and / or secondary amino groups in one molecule, at least one of which is a primary amino group. Examples of polyfunctional aromatic amines include compounds in which two amino groups are bonded to an aromatic ring at the ortho-, meta-, or para-positions, such as o-phenylenediamine, m-phenylenediamine (hereinafter referred to as "m-PDA", p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, and p-diaminopyridine; 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. In particular, from the viewpoint of obtaining a semipermeable membrane having excellent selectivity, permeability, and heat resistance, m-PDA, p-phenylenediamine, or 1,3,5-triaminobenzene is preferably used.

[0024] The term "polyfunctional aliphatic amine" refers to an aliphatic amine having two or more amino groups in one molecule. Examples of polyfunctional aliphatic amines include piperazine derivatives represented by the following general formula (I) and ethylenediamine.

[0025] [ka]

[0026] In general formula (I), R 1 , R 2 are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0027] Specific examples of piperazine derivatives include piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,5-diethylpiperazine, 2-n-propylpiperazine, 2,5-di-n-butylpiperazine, etc. In particular, piperazine or dimethylpiperazine is preferably used.

[0028] In the above step, at least one polyfunctional amine may be used, and two or more compounds may be selected from polyfunctional aromatic amines and polyfunctional aliphatic amines. Among these, it is preferable to use a polyfunctional aromatic amine as the polyfunctional amine, from the viewpoint of easily improving the performance of the semipermeable membrane.

[0029] In the treatment method according to the present embodiment, from the viewpoint of facilitating contact with functional groups inside the coarse pores through which the substance to be removed passes and shrinking the coarse pores, the molecular weight of the polyfunctional amine is preferably from 50 to 200, and more preferably from 80 to 120. For example, m-PDA can be preferably used as a polyfunctional aromatic amine that satisfies the above molecular weight range.

[0030] A "polyfunctional carboxylic acid" is a carboxylic acid having two or more carboxy groups in one molecule. Examples of polyfunctional carboxylic acids include oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3,5-benzenetricarboxylic acid (hereinafter referred to as "trimesic acid"), 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, and 1,4-benzenedicarboxylic acid. Among polyfunctional carboxylic acids, 1,3,5-benzenetricarboxylic acid is preferred.

[0031] In the above step, only one type of compound may be used as the polyfunctional carboxylic acid, or two or more types of compounds may be used in combination.

[0032] In the treatment method according to this embodiment, from the viewpoint of facilitating contact with the functional groups inside the coarse pores through which the substance to be removed passes and shrinking the coarse pores, the molecular weight of the polyfunctional carboxylic acid is preferably 300 or less, and more preferably 150 or more and 250 or less.

[0033] The term "condensing agent" refers to a compound that has the effect of activating an amino group, a carboxy group, or a hydroxy group, and promoting the formation of an amide group or an ester group.

[0034] Examples of the condensing agent include carbodiimide-based condensing agents, imidazole-based condensing agents, triazine-based condensing agents, phosphonium-based condensing agents, and uronium-based condensing agents.

[0035] Examples of carbodiimide condensing agents include N,N'-diisopropylcarbodiimide, N,N'-dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (hereinafter referred to as "EDC-HCl").

[0036] Examples of the imidazole-based condensing agent include N,N'-carbonyldiimidazole and 1,1'-carbonyldi(1,2,4-triazole).

[0037] Examples of triazine-based condensing agents include 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (hereinafter referred to as "DMT-MM"), 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one, O-(benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(3,4-dihydro-4-oxo-1,2,3-benzotriazin-3-yl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, and (4,6-dimethoxy-1,3,5-triazin-2-yl)-(2-octoxy-2-oxoethyl)dimethylammonium trifluoromethanesulfonate.

[0038] Examples of phosphonium-based condensing agents include 1H-benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate, (7-azabenzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate, bromotris(dimethylamino)phosphonium hexafluorophosphate, and chlorotripyrrolidinophosphonium hexafluorophosphate.

[0039] Examples of uronium condensing agents include O-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-(N-succinimidyl)-N,N,N',N'-tetramethyluronium tetrafluoroborate, O-(N-succinimidyl)-N,N,N',N'-tetramethyluronium hexafluorophosphate, S-(1-oxido-2-pyridyl)-N,N,N',N'-tetramethylthiuronium tetrafluoroborate, and O-[2-oxo-1(2H)-pyridyl]-N,N,N',N'-tetramethyluronium tetrafluoroborate.

[0040] In addition to the above, condensing agents such as {{[(1-cyano-2-ethoxy-2-oxoethylidene)amino]oxy}-4-morpholinomethylene}dimethylammonium hexafluorophosphate, 2-chloro-1,3-dimethylimidazolinium hexafluorophosphate, 1-(chloro-1-pyrrolidinylmethylene)pyrrolidinium hexafluorophosphate, 2-fluoro-1,3-dimethylimidazolinium hexafluorophosphate, fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate, and sulfuric acid can be used.

[0041] Among these, it is preferable to use a carbodiimide-based condensing agent or a triazine-based condensing agent. Furthermore, from the viewpoint of enabling condensation in an aqueous system, it is preferable to use EDC-HCl as a carbodiimide-based condensing agent or DMT-MM as a triazine-based condensing agent.

[0042] In the treatment method according to this embodiment, the time for which the polyamide-based semipermeable membrane is contacted with the solution containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent is preferably 10 minutes to 72 hours, more preferably 16 hours to 72 hours, and even more preferably 24 hours to 72 hours. When the semipermeable membrane is contacted with the solution for 10 minutes or longer, the carboxyl groups at the terminals of the polyamide in the separating functional layer are sufficiently activated, and the reaction with the polyfunctional amine proceeds. On the other hand, when the semipermeable membrane is contacted with the solution for 72 hours or less, the reagent is less likely to be deactivated by the atmosphere, and a decrease in the water permeability of the semipermeable membrane due to excessive reaction can be suppressed.

[0043] In the treatment method according to this embodiment, the ratio of the sum of the number of carboxyl groups in the polyfunctional carboxylic acid to the sum of the number of amino groups in the polyfunctional amine in a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent is preferably 0.5 or more and 2.0 or less. When the ratio of the sum of the number of carboxyl groups in the polyfunctional carboxylic acid to the sum of the number of amino groups in the polyfunctional amine falls within the above range, the degree of polymerization of the polyfunctional amine and the polyfunctional carboxylic acid is likely to be 2 or more, and coarse pores can be efficiently reduced. From the above viewpoints, the ratio of the sum of the number of carboxyl groups in the polyfunctional carboxylic acid to the sum of the number of amino groups in the polyfunctional amine in the contact solution is more preferably 0.8 or more and 1.2 or less, even more preferably 0.9 or more and 1.1 or less, and most preferably 1.0. When the ratio of the sum of the number of carboxyl groups in the polyfunctional carboxylic acid to the sum of the number of amino groups in the polyfunctional amine is 1.0, the molecular weight can be increased most, and coarse pores through which various sizes of target substances to be removed can be reduced.

[0044] In the method for treating a semipermeable membrane according to this embodiment, the polyfunctional amine concentration of the solution containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent is preferably 0.001% by mass to 0.050% by mass, more preferably 0.001% by mass to 0.010% by mass, and even more preferably 0.005% by mass to 0.010% by mass. The polyfunctional carboxylic acid concentration is preferably 0.005% by mass to 0.1% by mass, and more preferably 0.005% by mass to 0.010% by mass.

[0045] In the method for treating a semipermeable membrane according to this embodiment, the concentration of the condensing agent in the solution containing the polyfunctional amine, the polyfunctional carboxylic acid, and the condensing agent is preferably 0.03% by mass or more and 0.3% by mass or less, more preferably 0.03% by mass or more and 0.05% by mass or less.

[0046] The higher the concentrations of the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent in the solution containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent, the more improved the removal performance can be in a short reaction time. Furthermore, by setting the concentrations of the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent within the above ranges, the precipitation of polyamide produced by the reaction of the polyfunctional amine and the polyfunctional carboxylic acid in the solution can be suppressed.

[0047] In the method for treating a semipermeable membrane according to the present embodiment, from the viewpoint of sufficiently activating the carboxy groups of the polyfunctional carboxylic acid, the total number of moles of the condensing agent relative to the total number of moles of the carboxy groups of the polyfunctional carboxylic acid in the solution containing the polyfunctional amine, the polyfunctional carboxylic acid, and the condensing agent is preferably 0.1 or more and 1.5 or less, more preferably 0.5 or more and 1.5 or less, and even more preferably 1.0 or more and 1.5 or less.

[0048] Furthermore, the temperature of the solution containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent when brought into contact with the semipermeable membrane is preferably 10° C. or higher and 50° C. or lower, more preferably 20° C. or higher and 45° C. or lower. When the solution temperature is 10° C. or higher, the reaction is promoted, and when it is 50° C. or lower, deterioration of the semipermeable membrane is unlikely to occur.

[0049] Furthermore, in order to promote bonding between the carboxy group of the polyamide-based semipermeable membrane and the polyfunctional amine in the solution, or between the amino group of the polyamide-based semipermeable membrane and the polyfunctional carboxylic acid in the solution, the pH of the solution containing the polyfunctional amine, the polyfunctional carboxylic acid, and the condensing agent may be 10 or more and 13 or less.

[0050] The solution containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent can be brought into contact with the polyamide-containing separation functional layer of the semipermeable membrane in a state where the polyamide-based semipermeable membrane is incorporated into a semipermeable membrane element (hereinafter also referred to as "element"). For example, the semipermeable membrane may be immersed in the solution by supplying the solution to the element and then leaving it to stand, or the element may be immersed in the solution. Alternatively, the solution can be brought into contact with the separation functional layer by flowing it through the supply side flow path of the semipermeable membrane in the element.

[0051] In this embodiment, the semipermeable membrane is incorporated into a semipermeable membrane element, and it is preferable to perform the test on a semipermeable membrane element that exhibits at least one of a salt permeability that is 10% or more higher than the initial value and a neutral molecule permeability that is 10% or more higher than the initial value.

[0052] Here, the "initial value" refers to the salt permeability or neutral molecule permeability calculated by the following formula from the standard salt rejection rate or standard neutral molecule rejection rate listed on the element specification sheet. Salt penetration rate (%) = 100 - salt rejection rate (%) Neutral molecule permeability (%) = 100-neutral molecule removal rate (%).

[0053] (3) Other factors The solutions containing the polyfunctional amine, polyfunctional carboxylic acid and condensing agent may each contain compounds such as an acylation catalyst, a polar solvent, an acid scavenger, an antioxidant, etc., as necessary.

[0054] <Cleaning> Before contacting the semipermeable membrane with the solution containing the polyfunctional amine, the polyfunctional carboxylic acid, and the condensing agent, the polyamide-based semipermeable membrane may be washed with a chemical solution. By washing, fouling-causing substances deposited on the membrane surface can be removed.

[0055] Acids are mainly used to clean inorganic fouling (scale). Examples of acids used for cleaning include hydrochloric acid, nitric acid, sulfuric acid, citric acid, and oxalic acid. The lower the pH of the acid used for cleaning, the greater the cleaning effect, but the greater the deterioration of the semipermeable membrane. Therefore, the pH of the acid used for cleaning is preferably between 0 and 4, and more preferably between 1 and 3.

[0056] Alkali is mainly used to clean organic fouling. Examples of alkalis used for cleaning include sodium hydroxide and potassium hydroxide. The higher the pH of the alkali used for cleaning, the greater the cleaning effect. Therefore, the pH of the alkali used for cleaning is preferably 10 to 14, and more preferably 11 to 13.

[0057] Oxidizing agents are mainly used to clean biofouling, including hypochlorite, chlorinated isocyanurate, percarbonate, ozone, and potassium permanganate.

[0058] The cleaning agent may be one kind or a plurality of kinds.

[0059] <Semi-permeable membrane> The treatment method according to this embodiment can be widely applied to semipermeable membranes having a separation functional layer containing polyamide (polyamide-based semipermeable membranes). In particular, it is preferable to apply the treatment method to semipermeable membranes having the separation performance of reverse osmosis membranes or nanofiltration membranes.

[0060] The semipermeable membrane may be used in the form of a composite semipermeable membrane further comprising a support. The support may comprise a substrate and a porous support layer, or may consist of only a porous support layer.

[0061] The porous support layer is a porous layer having a denser structure than the substrate. The separation function layer is formed on the porous support layer, and the pore size of the surface of the porous support layer facing the separation function layer is, for example, 0.1 nm or more and 100 nm or less.

[0062] Materials that can be used to form the porous support layer include polysulfone, polyethersulfone, polyamide, polyester, cellulose-based polymers, vinyl polymers, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide. Examples of cellulose-based polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile.

[0063] The separating functional layer of the polyamide-based semipermeable membrane preferably contains a crosslinked polyamide as a main component. The main component means a component that accounts for 50% by mass or more of the components of the separating functional layer. The content of crosslinked polyamide in the separating functional layer is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0064] The term "crosslinked polyamide" refers to a polymer of a polyfunctional amine and a polyfunctional acid halide. In particular, the crosslinked polyamide is preferably a crosslinked aromatic polyamide, which is a polymer of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide.

[0065] As the polyfunctional aromatic amine, the compounds listed in the above "(2) Solution contact step" are preferably used, and as the polyfunctional aromatic acid halide, the compounds listed below are preferably used.

[0066] The term "polyfunctional acid halide" refers to an acid halide having two or more halocarbonyl groups in one molecule. The polyfunctional acid halide can form an amide bond by reacting with a terminal amino group.

[0067] Examples of polyfunctional acid halides that can be used include halides of oxalic acid, malonic acid, maleic acid, fumaric acid, glutaric acid, 1,3,5-cyclohexanetricarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, trimesic acid, 1,2,4-benzenetricarboxylic acid, 1,3-benzenedicarboxylic acid, and 1,4-benzenedicarboxylic acid. Among the acid halides, acid chlorides are preferred.

[0068] The polyfunctional acid halide is preferably a polyfunctional aromatic acid halide. Specifically, the term "polyfunctional aromatic acid halide" refers to an aromatic acid halide having at least two, preferably 2 to 4, carbonyl chloride groups in one molecule (i.e., a polyfunctional aromatic acid chloride). For example, a trifunctional acid halide may be trimesic acid chloride, and a bifunctional acid chloride may be biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, or naphthalenedicarboxylic acid chloride. These polyfunctional aromatic acid halides may be used alone or in combination of two or more.

[0069] The separation functional layer of the semipermeable membrane according to this embodiment is preferably formed by interfacial polymerization using an aqueous solution containing a polyfunctional aromatic amine and an organic solvent solution containing a polyfunctional aromatic acid halide. The interfacial polymerization process includes (i) applying an aqueous solution containing a polyfunctional aromatic amine to a support (or to the porous support layer if the support has a substrate and a porous support layer), and (ii) applying an organic solvent solution containing a polyfunctional aromatic acid halide to the support after the process (i) (or to the porous support layer if the support has a substrate and a porous support layer).

[0070] In steps (i) and (ii), the means for applying the solution include, for example, immersion, showering, and coating.

[0071] The organic solvent in which the polyfunctional aromatic acid halide is dissolved in step (ii) is immiscible with water and has a solubility parameter of 15.2 (MPa) or less. 1 / 2 It is preferable to use an organic solvent having an octanol / water partition coefficient of 3.2 or more. It is also preferable that the organic solvent does not destroy the support, particularly the porous support layer. Representative examples of organic solvents that satisfy the above conditions include octane, nonane, decane, undecane, dodecane, isododecane, tridecane, tetradecane, heptadecane, hexadecane, isodecane, cyclooctane, isooctane, ethylcyclohexane, 1-octene, 1-decene, and the like, either alone or in combination.

[0072] <Semipermeable membrane element> The semipermeable membrane is preferably used as a spiral-type semipermeable membrane element, which is wound around a cylindrical water collection pipe having many holes, together with a feed-side passage material such as a plastic net, a permeate-side passage material such as a tricot, and, if necessary, a film for increasing pressure resistance. Furthermore, this element can be connected in series or in parallel and housed in a pressure vessel to form a semipermeable membrane module.

[0073] Furthermore, semipermeable membranes, semipermeable membrane elements, and semipermeable membrane modules can be combined with a pump that supplies feed water to them, a device that pretreats the feed water, etc. to form a fluid separation device. By using this separation device, feed water can be separated into permeated water such as drinking water and concentrated water that has not permeated the membrane, thereby obtaining water that meets the intended purpose.

[0074] <Processing equipment> The semipermeable membrane element treatment device according to this embodiment, in order to perform the semipermeable membrane treatment method described above, includes a first tank for storing an aqueous solution containing a polyfunctional amine, a second tank for storing an aqueous solution containing a condensing agent, an element mounting section for mounting a semipermeable membrane element incorporating a semipermeable membrane having a separation functional layer containing at least one polyamide, piping connecting the first tank and the element mounting section, piping connecting the second tank and the element mounting section, a first pump between the first tank and the element mounting section, and a second pump between the second tank and the element mounting section. In this case, the polyfunctional carboxylic acid may be stored in the first tank together with the polyfunctional amine, or in the second tank together with the condensing agent. A third pump may be provided between a third tank and the element mounting section, and the aqueous solution containing the carboxylic acid may be stored in the third tank.

[0075] Specifically, the treatment device for semipermeable membrane elements according to this embodiment is configured to include a semipermeable membrane unit including a container in which a semipermeable membrane element is loaded as an element mounting part, piping connecting the semipermeable membrane unit to each tank, and a pump connected to the piping.

[0076] The pipes connecting the first tank and the second tank with the semipermeable membrane element are preferably connected so that each solution is supplied from the separating function layer side of the semipermeable membrane.

[0077] The treatment device may further include a tank for a cleaning solution, a pump, piping, etc. The polyamide-based semipermeable membrane to be treated by the treatment method of the present invention is a semipermeable membrane whose removal performance does not reach the desired level or whose removal performance has decreased. For example, the removal performance can be improved by carrying out the above-mentioned process on a semipermeable membrane that has been subjected to the above-mentioned cleaning treatment, specifically, a semipermeable membrane that has been contacted with at least one chemical selected from the group consisting of an acid having a pH of 4 or less, an alkali having a pH of 10 or more, and an oxidizing agent.

[0078] The present invention also provides a method for producing a semipermeable membrane element, which comprises a step of treating a polyamide-based semipermeable membrane with a treatment method comprising the steps described above.

[0079] <Supply method> The polyfunctional amine, polyfunctional carboxylic acid, and condensing agent may be supplied simultaneously from separate pipes, or a solution in which two of them have been mixed in advance and the remaining solution may be supplied simultaneously from separate pipes, or a solution in which all three of them have been mixed in advance may be supplied. Among these, a method in which solutions containing the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent are supplied simultaneously from separate pipes, or a solution in which two of them have been mixed in advance and the remaining solution may be supplied simultaneously from separate pipes, is preferred. When a solution in which all three of them have been mixed in advance is used, it is preferable to mix them immediately before supplying them to the separation membrane element. In a solution in which all three of them have been mixed in advance, the polyfunctional amine, polyfunctional carboxylic acid, and condensing agent coexist, and the polyfunctional amine and polyfunctional carboxylic acid react in the solution to produce high molecular weight substances such as oligomers, which may reduce the efficiency of improving the performance of the semipermeable membrane. [Example]

[0080] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0081] (membrane flux) Evaluation water (TDS concentration 3.5%, boron concentration approximately 5 ppm) adjusted to pH 6.5 was supplied to the element at an operating pressure of 5.5 MPa and a recovery rate of 8%, and the amount of water passing through the membrane after 24 hours of membrane filtration treatment was measured. The membrane permeation flux (m ) was calculated as the amount of water passing through (cubic meters) per day per square meter of membrane surface. 3 / m 2 "TDS" stands for total dissolved solids, and according to its definition expressed as "mass / volume" or "mass ratio," it can be calculated from the mass of the residue obtained by evaporating a solution filtered through a 0.45 μm filter at a temperature of 39.5°C to 40.5°C, but the value converted from the practical salinity (S) was used.

[0082] (Salt removal rate, boron removal rate) Evaluation water adjusted to pH 6.5 (TDS concentration 3.5%, boron concentration approximately 5 ppm) was supplied to the element at an operating pressure of 5.5 MPa and a recovery rate of 8%. After 24 hours of membrane filtration, the salt concentration of the supply water and permeate was determined by conductivity measurement, and the boron concentration was determined using an ICP optical emission spectrometer (Agilent Technologies 5110 ICP-OES). The salt rejection rate and boron rejection rate were calculated using the following formula. Salt rejection rate (%) = 100 x {1 - (salt concentration of permeate water / salt concentration of evaluation water)} Boron removal rate (%) = 100 × {1 - (boron concentration in permeate water / boron concentration in evaluation water)}.

[0083] (Accelerated aging treatment) Evaluation water adjusted to pH 6.5 (TDS concentration 3.5%, boron concentration approximately 5 ppm) was supplied to the element at an operating pressure of 5.5 MPa and a recovery rate of 8%, and after membrane filtration for 24 hours, a sodium hypochlorite solution (100 ppm) was supplied to the element at 25°C and allowed to stand for 24 hours. The contents of the element were then replaced with pure water. Next, a sodium hydroxide aqueous solution at pH 13.0 was supplied at 25°C and allowed to stand for 24 hours. The contents of the element were then replaced with pure water. Furthermore, a solution containing sulfuric acid at pH 1.0 was supplied at 25°C and allowed to stand for 24 hours. The contents of the element were then replaced with pure water.

[0084] (Membrane permeation flux ratio, salt permeation ratio, boron permeation ratio) The membrane permeation flux ratio, salt permeability ratio, and boron permeability ratio were calculated from the following formulas. Membrane permeation flux ratio = (membrane permeation flux after accelerated aging treatment or after solution contact step) / (membrane permeation flux before accelerated aging treatment) Salt permeability ratio = {100 - (salt removal rate after accelerated aging treatment or solution contact step)} / {100 - (salt removal rate before accelerated aging treatment)} Boron transmittance ratio = {100 - (boron removal rate after accelerated aging treatment or solution contact step)} / {100 - (boron removal rate before accelerated aging treatment)}.

[0085] [Reference example 1] The performance of the TM810V reverse osmosis membrane element for seawater desalination, manufactured by Toray Industries, Inc., equipped with a polyamide semipermeable membrane, was evaluated (membrane permeation flux, salt rejection rate, and boron rejection rate). The performance evaluation results are shown in Table 3.

[0086] [Reference example 2] Accelerated aging treatment was performed on a TM810V reverse osmosis membrane element for seawater desalination manufactured by Toray Industries, Inc. The performance evaluation results of the element after accelerated aging treatment are shown in Table 3.

[0087] [Example 1] A solution contact step was carried out in which an aqueous solution containing 0.050% by mass of m-PDA, 0.063% by mass of trimesic acid, and 0.250% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 for 2 hours at 40° C. The performance evaluation results are shown in Table 3.

[0088] [Example 2] The solution contact step was carried out in the same manner as in Example 1, except that the treatment time was changed to 16 hours. The performance evaluation results are shown in Table 3. By changing the treatment time to 16 hours, the performance of the semipermeable membrane element was improved compared to Example 1, and was improved to nearly the performance of Reference Example 1 before the accelerated aging treatment. Furthermore, deposition of a precipitate that was thought to be polyamide formed by the reaction of the polyfunctional amine and polyfunctional carboxylic acid in the solution was observed on the membrane surface.

[0089] [Example 3] The solution contact step was carried out in the same manner as in Example 1, except that the treatment time was changed to 24 hours. The performance evaluation results are shown in Table 3. By changing the treatment time to 24 hours, the removal performance of the semipermeable membrane element was improved compared to Example 1, but the permeation flux was lower than in Example 2. Note that, as in Example 2, significant deposition of precipitates was observed on the membrane surface.

[0090] [Example 4] The solution contact step was carried out in the same manner as in Example 2, except that the condensing agent concentration was set to 0.5% by mass. The performance evaluation results are shown in Table 3. Even when the condensing agent concentration was increased, the performance was almost the same as in Example 2. Note that, as in Example 2, significant deposition of precipitates was observed on the membrane surface.

[0091] [Example 5] A solution contact step treatment was carried out in the same manner as in Example 2, except that the condensing agent concentration was set to 0.05% by mass. The performance evaluation results are shown in Table 3. Although an improvement in the performance of the element was observed, the performance did not reach that of Example 2 due to the low condensing agent concentration.

[0092] [Example 6] A solution contact step was carried out in which an aqueous solution containing 0.013 mass % m-PDA, 0.016 mass % trimesic acid, and 0.063 mass % DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40°C for 24 hours. The performance evaluation results are shown in Table 3. Since the concentrations of each reagent were one-fourth of those in Example 2, the treatment time had to be extended, but the performance of the semipermeable membrane element was equivalent to that in Example 2 and improved to nearly the performance of Reference Example 1 before the accelerated aging treatment. In addition, slight precipitation of precipitates was observed.

[0093] [Example 7] A solution contact step was carried out in which an aqueous solution containing 0.008% by mass of m-PDA, 0.010% by mass of trimesic acid, and 0.042% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40°C for 24 hours. The performance evaluation results are shown in Table 3. The performance of the semipermeable membrane element was sufficiently improved, but due to the low concentrations of each reagent, it did not reach the performance of Examples 3 and 6, which had the same treatment time of 24 hours. On the other hand, no precipitation was observed.

[0094] [Example 8] The solution contact step was carried out in the same manner as in Example 7, except that the treatment time was changed to 48 hours. The performance evaluation results are shown in Table 3. By extending the treatment time, the performance of the semipermeable membrane element was improved compared to Example 7, and was improved to nearly the performance of Reference Example 1 before the accelerated aging treatment. No precipitation was observed.

[0095] [Example 9] The solution contact step was carried out in the same manner as in Example 7, except that the treatment time was changed to 72 hours. The performance evaluation results are shown in Table 3. By extending the treatment time, the performance of the semipermeable membrane element was further improved compared to Example 8. Furthermore, no precipitation of precipitates was observed.

[0096] [Example 10] The solution contact step was carried out in the same manner as in Example 9, except that the treatment temperature was changed to 25°C. The performance evaluation results are shown in Table 3. The performance of the semipermeable membrane element was sufficiently improved, but did not reach the performance of Example 9 due to the low treatment temperature. No precipitation was observed.

[0097] [Example 11] The solution contact step was carried out in the same manner as in Example 9, except that the concentration of m-PDA was changed to 0.004% by mass. The performance evaluation results are shown in Table 3. The performance of the semipermeable membrane element was improved to the same level as in Example 10, but the removal rate did not reach that of Example 7 because the sum of the numbers of carboxyl groups relative to the sum of the numbers of amino groups was greater than 1.

[0098] [Example 12] The solution contact step was carried out in the same manner as in Example 9, except that the concentration of m-PDA was changed to 0.014% by mass. The performance evaluation results are shown in Table 3. The performance of the semipermeable membrane element was inferior to that of Example 9.

[0099] [Example 13] A solution contact step was carried out in which an aqueous solution containing 0.006% by mass of m-PDA, 0.008% by mass of trimesic acid, and 0.031% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40°C for 24 hours. The performance evaluation results are shown in Table 3. An improvement in the performance of the semipermeable membrane element was observed, but because the concentrations of each reagent were reduced to one-eighth of those in Example 1, it did not reach that of Example 7.

[0100] [Example 14] A solution contact step was carried out in which an aqueous solution containing 0.010% by mass of m-PDA, 0.031% by mass of trimesic acid, and 0.125% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40° C. for 72 hours. The performance evaluation results are shown in Table 3.

[0101] [Example 15] A solution contact step was carried out in which an aqueous solution containing 0.017% by mass of m-PDA, 0.008% by mass of trimesic acid, and 0.031% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40° C. for 72 hours. The performance evaluation results are shown in Table 3.

[0102] [Example 16] A solution contact step was carried out in which an aqueous solution containing 0.03% by mass of piperazine, 0.006% by mass of trimesic acid, and 0.250% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40° C. for 24 hours. The performance evaluation results are shown in Table 3.

[0103] [Example 17] A solution contact step was carried out in which an aqueous solution containing 0.010% by mass of piperazine, 0.002% by mass of trimesic acid, and 0.080% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 at 40° C. for 72 hours. The performance evaluation results are shown in Table 3.

[0104] [Comparative Example 1] A solution contact step was carried out in which an aqueous solution containing 0.050% by mass of m-PDA and 0.100% by mass of DMT-MM was supplied to the semipermeable membrane element obtained in Reference Example 2 for 1.5 hours at 25° C. The performance evaluation results are shown in Table 3.

[0105] Comparative Example 2 A solution contact step was carried out in which an aqueous solution containing 0.050% by mass of trimesic acid and 0.100% by mass of DMT-MM was supplied to the semipermeable membrane element described in Reference Example 2 for 1.5 hours at 25° C. The performance evaluation results are shown in Table 3.

[0106] Comparative Example 3 A solution contact step was carried out in which an aqueous solution containing 0.050% by mass of m-PDA and 0.050% by mass of trimesic acid was supplied to the semipermeable membrane element described in Reference Example 2 for 2 hours at 40° C. The performance evaluation results are shown in Table 3.

[0107] In Comparative Example 1, the solution did not contain a polyfunctional carboxylic acid, in Comparative Example 2, a polyfunctional amine, and in Comparative Example 3, the solution did not contain a condensing agent, so the reaction with the polyamide in the separation functional layer did not proceed, and the performance of the semipermeable membrane element did not improve.

[0108] [Table 1]

[0109] [Table 2]

[0110] [Table 3] [Industrial Applicability]

[0111] The treatment method of the present invention can be used as a method for improving the removal performance of semipermeable membranes for treating, for example, water containing salt or harmful substances, industrial wastewater, domestic wastewater, and the like.

Claims

1. A method for treating a semipermeable membrane, comprising the step of contacting a semipermeable membrane having a separating functional layer containing a polyamide with a solution containing a polyfunctional amine, a polyfunctional carboxylic acid, and a condensing agent.

2. 2. The treatment method according to claim 1, wherein the ratio of the total number of carboxyl groups of the polyfunctional carboxylic acid to the total number of amino groups of the polyfunctional amine in the solution is 0.5 or more and 2.0 or less.

3. The treatment method according to claim 1 or 2, wherein the concentration of the condensing agent in the solution is 0.03% by mass or more and 0.3% by mass or less.

4. 3. The treatment method according to claim 1, wherein the ratio of the total number of moles of the condensing agent to the total number of carboxy groups of the polyfunctional carboxylic acids in the solution is 0.5 or more and 1.5 or less.

5. The treatment method according to claim 1 or 2, wherein the concentration of the polyfunctional amine in the solution is 0.001% by mass or more and 0.010% by mass or less.

6. 3. The treatment method according to claim 1, wherein the condensing agent is a carbodiimide-based condensing agent or a triazine-based condensing agent.

7. 3. The treatment method according to claim 1, wherein the polyfunctional amine has a molecular weight of 50 or more and 200 or less.

8. 3. The treatment method according to claim 1, wherein the polyfunctional carboxylic acid has a molecular weight of 150 or more and 300 or less.

9. 3. The treatment method according to claim 1, wherein the time for which the solution is in contact with the semipermeable membrane is from 10 minutes to 72 hours.

10. The semipermeable membrane is incorporated into a semipermeable membrane element, The treatment method according to claim 1 or 2, wherein the treatment is performed on the semipermeable membrane element that exhibits at least one of a salt permeability that is 10% or more higher than the initial value and a neutral molecule permeability that is 10% or more higher than the initial value.

11. 3. The treatment method according to claim 1, wherein the treatment is carried out on a semipermeable membrane that has been contacted with at least one selected from the group consisting of an acid having a pH of 4 or less, an alkali having a pH of 10 or more, and an oxidizing agent.

12. A method for producing a semipermeable membrane having a separating functional layer containing a polyamide, the method comprising the treatment method according to claim 1 or 2.

13. A method for manufacturing a semipermeable membrane element, comprising subjecting the semipermeable membrane incorporated in the semipermeable membrane element to the treatment method according to claim 1 or 2.

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