Composite separation membrane and production method therefor

Abstract

The purpose of the present invention is to provide: a composite separation membrane which has excellent resistance to organic solvents and is capable of stable separations even in organic solvents; and a method by which the composite separation membrane can be easily produced. This composite separation membrane is characterized by including a support membrane comprising a modified poly(phenylene oxide) and a separation function layer comprising a crosslinked cationic polymer, the modified poly(phenylene oxide) having a sulfonic acid group and / or a sulfuric acid group and a polar group, and the separation function layer being formed on the support membrane.

Description

Composite separation membrane and method for producing the same

[0001] The present invention relates to a composite separation membrane capable of stable separation even in an organic solvent, and a method for easily producing the composite separation membrane.

[0002] In many industrial fields, including the chemical, pharmaceutical, and petrochemical industries, separation operations using organic solvents as a medium are indispensable, and in many cases, the distillation process is adopted. While distillation is a highly reliable technology, it consumes a lot of energy and generates a large carbon dioxide emission load, which has become a social issue.

[0003] On the other hand, membrane separation has the advantage of significantly reducing the energy required for separation compared to distillation because it does not involve a phase transition. Furthermore, because it is a process that does not require heating, it is also suitable for purifying substances that are prone to thermal degradation. Therefore, membrane technology is being applied in a wide range of industrial fields, including seawater desalination, drinking water treatment, sewage treatment, and blood purification.

[0004] Conventional membrane separations have almost always used water as the medium, but if membrane separations could be performed using organic solvents, the range of applications could be greatly expanded.

[0005] The technology of separating, purifying, and concentrating molecules with sizes ranging from a few angstroms to a few nanometers using a membrane with an organic solvent as a medium is called organic solvent nanofiltration (OSN) or organic solvent reverse osmosis (OSRO). Challenges with this technology include the tendency of organic polymer separation membranes to experience changes in pore size due to swelling of the membrane by the organic solvent and deterioration of performance over time. Therefore, there is a demand for nanofiltration membranes and reverse osmosis membranes that are stable over long periods and capable of high-precision molecular fractionation.

[0006] A composite membrane structure is preferred for the separation membrane used in OSN or OSRO, as it combines excellent molecular fractionation and a high permeation flow rate. A solvent-resistant porous membrane is selected as the support membrane, and a three-dimensionally crosslinked polymer thin film is typically formed on the support membrane as the separation functional layer. Techniques for forming the separation functional layer include, for example, interfacial polymerization, coating, and polymer adsorption using Layer-by-Layer (LbL). These methods are suitable for forming thin films with few defects and pore sizes of a few angstroms. Among these, LbL is a promising candidate for the separation layer of a composite membrane in OSN or OSRO, as it can form a separation layer by a simple process of contacting the membrane surface with an aqueous solution of a polymer electrolyte. Therefore, an LbL adsorption layer with excellent permeation selectivity and long-term stability in organic solvent systems is required.

[0007] The support membrane material for polymer composite membranes must be easy to fabricate and resistant to various organic solvents. Furthermore, because separation processes in pharmaceuticals and fine chemistry often require the treatment of solvents containing high concentrations of acid or base, it is desirable for the material to be resistant to acid and base attack. Materials considered for conventional solvent-resistant membranes include crosslinked amorphous polymers such as polyimide and polybenzimidazole. Membranes made of semi-crystalline polymers such as polyether ether ketone and polyphenylene sulfide have also been considered. Among these, polyimide and polybenzimidazole may not perform sufficiently well in terms of resistance to hydrolysis caused by acids or alkalis. Semi-crystalline polymers such as polyether ether ketone and polyphenylene sulfide have excellent hydrolysis resistance, but they can be difficult to fabricate because they dissolve only in very limited solvents, such as sulfuric acid, or not at all.

[0008] Separation membranes formed from polyphenylene oxide (PPO) or its derivatives are known to have excellent mechanical strength and alkali and acid resistance. Furthermore, PPO, despite being an amorphous polymer, is resistant to aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO). Therefore, PPO is considered to have excellent potential as a membrane material applicable to filtration processes using these pure solvents as media, as well as organic solvent filtration processes containing alkalis or acids.

[0009] As an example of a composite membrane that applies LbL, the present inventors have developed a composite membrane that exhibits excellent permeation selectivity in nanofiltration or reverse osmosis separation by sulfonating the surface of a PPO membrane with sulfuric acid to obtain an anionic membrane surface, and then adsorbing and crosslinking a separation functional layer of cationic polyvinyl alcohol (Patent Document 1).

[0010] Patent No. 7226569

[0011] As described above, composite separation membranes using a PPO membrane as a support membrane and exhibiting excellent permeability have been developed. However, if the resistance of the composite separation membrane to organic solvents could be further improved, it is believed that the range of application would be greatly expanded. Therefore, an object of the present invention is to provide a composite separation membrane that has excellent organic solvent resistance and is capable of stable separation even in organic solvents, and a method for easily producing the composite separation membrane.

[0012] The present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that in an asymmetric membrane having a separation functional layer formed on a support membrane, the resistance to organic solvents can be significantly improved by introducing polar groups into the support membrane in addition to sulfonic acid groups / sulfuric acid groups. This finding led to the completion of the present invention. The present invention is described below.

[0013] [1] A composite separation membrane comprising a support membrane made of modified polyphenylene oxide and a separation functional layer made of a crosslinked cationic polymer, wherein the modified polyphenylene oxide has sulfonic acid groups and / or sulfate groups and polar groups, and the separation functional layer is formed on the support membrane. [2] The composite separation membrane according to [1], wherein the sulfonic acid groups and / or sulfate groups and the polar groups are introduced into the benzene rings of the modified polyphenylene oxide via linker groups. [3] The composite separation membrane according to [2], wherein the benzene rings of the modified polyphenylene oxide have sulfonate methyl groups. [4] The composite separation membrane according to any one of [1] to [3], wherein the polar groups are one or more polar groups selected from a hydroxyl group, an ether group, a sulfonyl group, and an amino group. [5] The composite separation membrane according to any one of [1] to [4], wherein the cationic polymer is a cationic polyvinyl alcohol copolymer containing a structural unit having a quaternary ammonium cation group. [6] The composite separation membrane according to any one of [1] to [4], wherein the cationic polymer is one or more polyamines selected from polyethyleneimine, polyvinylamine, and polyallylamine.

[0014] [7] A method for producing a composite separation membrane, comprising the steps of: obtaining a support membrane using polyphenylene oxide; contacting the support membrane with a sulfonating agent to introduce sulfonic acid groups and / or sulfate groups into the support membrane; contacting the support membrane with the sulfonic acid groups and / or sulfate groups introduced therein with an aqueous solution containing a cationic polymer to form a cationic polymer layer on the support membrane; crosslinking the cationic polymer in the cationic polymer layer; and introducing polar groups into the polyphenylene oxide in the support membrane. [8] The method according to [7], wherein a support membrane made of polyphenylene oxide having halomethyl groups introduced into its benzene ring is contacted with an aqueous solution containing a sulfite as the sulfonating agent to introduce the sulfonic acid groups into the halomethyl groups. [9] The method according to [7], wherein the polar groups are introduced by reacting the polyphenylene oxide having halomethyl groups introduced into its benzene ring with monoethanolamine represented by the following formula (IV): [In the formula, R 21 is H or C 1-6 represents an alkyl group.]

[0015]

[10] Use of a composite separation membrane for treating a liquid to be treated by passing the liquid through the composite separation membrane, wherein the composite separation membrane has a support membrane made of modified polyphenylene oxide and a separation functional layer made of a crosslinked cationic polymer, the modified polyphenylene oxide having sulfonic acid groups and / or sulfate groups and polar groups, and the separation functional layer being formed on the support membrane.

[11] The use according to

[10] , wherein the liquid to be treated contains an organic solvent.

[12] The use according to

[10] or

[11] , wherein the sulfonic acid groups and / or sulfate groups and the polar groups are introduced into the benzene ring of the modified polyphenylene oxide via a linker group.

[13] The use according to

[12] , wherein the benzene ring of the modified polyphenylene oxide has a methyl sulfonate group.

[14] The use according to any of

[10] to

[13] , wherein the polar group is one or more polar groups selected from a hydroxyl group, an ether group, a sulfonyl group, and an amino group.

[15] The use according to any one of

[10] to

[14] above, wherein the cationic polymer is a cationic polyvinyl alcohol copolymer containing a structural unit having a quaternary ammonium cationic group.

[16] The use according to any one of

[10] to

[14] above, wherein the cationic polymer is one or more polyamines selected from polyethyleneimine, polyvinylamine, and polyallylamine.

[0016] The composite separation membrane of the present invention exhibits excellent durability against organic solvents. Furthermore, since the support membrane of the composite separation membrane of the present invention is made of modified polyphenylene oxide, it also has excellent acid resistance and alkali resistance. Therefore, the composite separation membrane of the present invention can be applied to filtration and reverse osmosis separation not only in aqueous systems but also in organic solvent systems, making it extremely advantageous from an industrial perspective.

[0017] Fig. 1 is a schematic diagram of each manufacturing process of the composite separation membrane according to the present invention, and the membrane configuration in each process. Fig. 2 (1) is a graph showing the relationship between the reaction temperature and the sulfur element ratio when the reaction time is fixed at 30 minutes and when a phase transfer catalyst (TBAB) is used and when it is not used. Fig. 2 (2) is a graph showing the relationship between the reaction temperature and the bromine element ratio when the reaction time is fixed at 30 minutes and when a phase transfer catalyst (TBAB) is used and when it is not used. Fig. 2 (3) is a graph showing the relationship between the reaction time and the sulfur element ratio (left axis) and the bromine element ratio (right axis) when the reaction temperature is fixed at 98 ° C and when a phase transfer catalyst (TBAB) is not used. Fig. 3 (1) is the result of analyzing a BrPPO membrane having bromomethyl groups, a sulfonated support membrane A, and a support membrane without a separation functional layer and into which an MEA was introduced after sulfonation, by infrared absorption spectroscopy. Fig. 3 (2) is a graph showing the relationship between the reaction temperature and the bromine element ratio when the reaction time is fixed at 98 ° C and when it is not used. -1 This is an enlarged view of the front and back.

[0018] Hereinafter, the method for producing a composite separation membrane according to the present invention will be described step by step, but the present invention is not limited to the following specific examples. In this disclosure, "sulfonic acid group and / or sulfate group" means "one or more groups selected from the group consisting of sulfonic acid group and sulfate group," and may be abbreviated as "sulfonic acid group / sulfate group."

[0019] 1. Film Forming Step In this step, a support film is obtained using polyphenylene oxide. Hereinafter, polyphenylene oxide is abbreviated as "PPO." PPO is a polymer having the following unit structure (I), for example, the following unit structure (I 1 Poly(2,6-dimethyl-1,4-phenylene oxide) having the following unit structure (I) substituted with a halogenomethyl group is widely used as a raw material because of the ease of introducing sulfonic acid groups. 2 ) may be used.

[0020] [In the formula, X represents a halogeno group selected from chloro, bromo, and iodo, and bromo is preferred because it has high leaving ability, is inexpensive, and is easy to handle.]

[0021] The physical properties of the raw material PPO are not particularly limited, and a desired PPO may be appropriately synthesized or a PPO product may be appropriately selected. For example, the weight-average molecular weight of PPO is preferably 5,000 or more from the viewpoint of imparting sufficient viscosity to the membrane-forming solution to improve coatability and spinnability and ensuring membrane strength. Furthermore, from the viewpoint of handling such as solubility, the weight-average molecular weight of PPO is preferably 500,000 or less. The weight-average molecular weight is preferably 10,000 or more, and preferably 400,000 or less.

[0022] The raw material PPO may be PPO having a methyl group or a halomethyl group introduced into the benzene ring. The benzyl cation is stable due to conjugation with the benzene ring, and PPO having a methyl group or a halomethyl group introduced into the benzene ring is highly reactive. For example, poly(2,6-dimethyl-1,4-phenylene oxide) is commercially available.

[0023] A halogeno group can be easily introduced into the methyl group substituted on the benzene ring of PPO. As the halogeno group, one or more halogeno groups selected from chloro, bromo, and iodo can be used, and bromo is preferably used because it has high leaving ability, is inexpensive, and is easy to handle.

[0024] The methyl groups substituted on the benzene ring of PPO can be halogenated using conventional methods. For example, a halogenating agent can be added to a solution of PPO having methyl groups. Examples of solvents that can be used include halogenated aliphatic hydrocarbon solvents such as dichloromethane, chloroform, and carbon tetrachloride; halogenated aromatic hydrocarbon solvents such as chlorobenzene; and aromatic hydrocarbon solvents such as benzene and toluene. These solvents have low halogen solubility and can keep the halogen concentration in the reaction system low, so halogenation at the benzyl position is prioritized. On the other hand, it is known that when a polar solvent such as acetonitrile is used, halogenation at the benzene ring is prioritized. However, even when the above-mentioned solvents are used, there is a possibility that the benzene ring may be directly halogenated in addition to the benzyl position. From the standpoint of ease of handling, halogenated aromatic hydrocarbon solvents such as chlorobenzene are preferred.

[0025] As the halogenating agent, for example, N-halogenosuccinimide such as N-bromosuccinimide or a simple halogen can be used.

[0026] The halogenation conditions may be adjusted as appropriate. For example, it is preferable to carry out the reaction at 110°C or higher for 3 hours or longer under an inert atmosphere such as argon or nitrogen. The higher the reaction temperature, the higher the selectivity of halogenation at the benzyl position. However, from the viewpoint of suppressing side reactions, it is preferable to carry out the halogenation reaction at 115°C or higher but lower than 135°C.

[0027] After the reaction is complete, the halogenated PPO may be purified by a conventional method. For example, a poor solvent may be added to the reaction mixture after the reaction to precipitate the halogenated PPO, which may then be filtered, washed with a poor solvent, and dried. Examples of the poor solvent that can be used include alcohol solvents such as methanol and ethanol; and ketone solvents such as acetone and methyl ethyl ketone. Methanol is preferred for its simplicity.

[0028] In the present disclosure, the degree of halogenation at the benzyl position of PPO can be determined by, for example, nuclear magnetic resonance (NMR) using deuterated chloroform as a solvent. An example of the chemical structure of halogenated PPO is shown below. However, halogenated PPO does not have a unit structure that does not have a halogeno group, i.e., R 1 ~R 8 may also include a unit structure in which all of the units are H. Various unit structures can be produced depending on the degree of halogenation of the benzene ring and the benzyl position, and the abundance ratio of each unit structure can be determined based on each characteristic peak in NMR. Detailed unit structures can also be identified using, for example, heteronuclear single quantum coherence spectroscopy (HSQC).

[0029]

[0030] [In the formula, R 1 ~R 8 each independently represents a halogeno group or H, R 1 and R 2 represents a halogeno group on a benzene ring, R 3 ~R 8represents a halogeno group at the benzyl position, i is an integer of 1 to k, which indicates that the unit structure is the i-th structure among the k unit structures identified by NMR, and n i represents a number of 0 to 1, which is the mole fraction of the i-th structure among the k types of unit structures.

[0031] In the present invention, the degree of halogenation D is determined by the average number of halogen atoms substituted at the benzyl position per unit structure. Hal is defined and represented by the following formula (1). For example, in the case of PPO having two methyl groups at the 2- and 6-positions in the unit structure, the number of hydrogen atoms at the benzyl positions at which substitution can occur is six, so D Hal can take a value of 0 or more and 6.0 or less. However, as far as the inventors know, in the majority of cases, one hydrogen atom per methyl group is substituted with a halogeno group, and there are also a certain number of cases in which two hydrogen atoms are substituted with halogeno groups. On the other hand, no cases have been observed in which three hydrogen atoms per methyl group are substituted with halogeno groups.

[0032] [In the formula, N i_BzHal represents the number of halogeno groups at the benzyl position in each unit structure of the above formula (II), and n i indicates the molar fraction of each structural unit of the above formula (II).

[0033] The average number of halogeno groups substituted on the benzene ring per unit structure is represented by the following formula (2).

[0034] [In the formula, N i_ArHal represents the number of halogeno groups substituted on the benzene ring in each unit structure of the above formula (II), and n i indicates the molar fraction of each structural unit of the above formula (II).

[0035] The degree of halogenation D at the benzyl position Hal is preferably 0.5 or more and 2.0 or less. Hal If the halogenation degree D is 0.5 or more, the methyl groups on the benzene rings of the PPO are sufficiently halogenated, and the PPO is more susceptible to attack by a nucleophilic agent, as described below, and as a result, the hydrophilicity and solvent resistance of the modified PPO are more reliably improved. HalWhen the ratio is 2.0 or less, there is no need to use an excessive amount of halogenating agent, which is economical, and side reactions such as crosslinking reactions during the reaction can be sufficiently suppressed.

[0036] In the present disclosure, the degree of halogenation D of the benzene ring Hal2 is not particularly limited, but is preferably 0 or more and 1.0 or less. Hal2 If the value is 1.0 or less, the degree of halogenation at the benzyl position D Hal This can prevent the relative excessive decrease of D, and there is no need to use an excessive amount of a halogenating agent, which is economical. Furthermore, the solvent resistance of the modified PPO can be more reliably ensured. Hal2 Although a lower value is preferable, in reality it is equal to or greater than 0. Depending on the reaction conditions, there may be a unit structure in which both the benzene nucleus and the benzyl position are halogenated.

[0037] In this step, a support membrane is produced from raw PPO. As the raw PPO, unsubstituted PPO may be used as described above, or PPO having a methyl group on the benzene ring, such as 2,6-dimethyl-1,4-phenylene oxide, may be used, or PPO having a halomethyl group on the benzene ring may be used. However, it is preferable not to use PPO into which sulfonic acid groups / sulfate groups have been introduced as the raw material. The introduction of sulfonic acid groups / sulfate groups may reduce the solubility of PPO, making it difficult to form a membrane. Furthermore, by introducing sulfonic acid groups / sulfate groups after membrane formation, more sulfonic acid groups / sulfate groups are introduced to the surface of the support membrane, thereby improving the efficiency of adsorption of the cationic polymer.

[0038] The form of the support membrane is not particularly limited, and may be, for example, a flat membrane or a hollow fiber membrane.

[0039] The support membrane can be produced, for example, by applying a solution of raw PPO to a substrate such as a nonwoven fabric or a filter using a doctor blade or the like, followed by drying. The solvent for dissolving the raw PPO is not particularly limited as long as it can dissolve the raw PPO well, and examples of such solvents include water-soluble organic solvents such as amide solvents, such as N-methylpyrrolidone, dimethylacetamide, and dimethylformamide. Furthermore, since the support membrane must be porous with interconnecting pores in order to be used as a separation membrane, a water-soluble pore-forming material may be added to the raw PPO solution. Examples of pore-forming materials include polyethylene glycol, glycerin, polypropylene glycol, nonionic surfactants, and ionic surfactants.

[0040] The substrate is not particularly limited as long as it has excellent solvent resistance and can effectively support the support membrane. Examples include nonwoven fabrics made of solvent-resistant materials such as polyethylene terephthalate, polyethylene, polypropylene, and polyphenylene sulfide. Polyphenylene sulfide (PPS) is preferred as the substrate material. PPS has excellent solvent resistance and is also resistant to alkalis and acids. A support membrane can be obtained by applying a raw PPO solution to the substrate and then immersing it in a coagulation bath of a non-solvent such as water. Furthermore, when producing a hollow fiber membrane, the raw PPO solution is extruded together with the inner liquid from a double cylindrical nozzle and immersed in a coagulation bath. After forming the support membrane, the substrate may be peeled off from the support membrane or used as is as part of the composite separation membrane.

[0041] In the above-mentioned membrane-forming process, conditions such as the PPO concentration and discharge temperature of the raw PPO solution, the temperature and composition of the coagulation bath, and the transport speed of the support membrane may be appropriately set based on publicly known knowledge. The porosity of the support membrane can be adjusted by the concentration of the pore-forming agent in the raw PPO solution.

[0042] After the reaction, the support membrane may be subjected to conventional post-treatment, for example, by thoroughly washing the support membrane with water to remove the solvent and the pore-forming agent, thereby making the support membrane porous.

[0043] 2. Sulfonic acid group / sulfuric acid group introduction step In this step, sulfonic acid groups (-SO3H) and / or sulfate groups (-OSO3H) are introduced into the support membrane prepared in step 1 by contacting it with a sulfonating agent. In this disclosure, sulfonic acid groups / sulfuric acid groups include ionized -SO3 - / -OSO3 - and their salts -SO3 - M + / -OSO3 - M + (Wherein M is Na + Ya K + The term "sulfonation" refers to the introduction of sulfonic acid groups or sulfate groups. In this process, sulfonation of the surface of the support membrane in particular imparts a negative charge (Figure 1).

[0044] The conditions for introducing sulfonic acid groups into at least the surface of the support membrane are not particularly limited. For example, the support membrane obtained in step 1 is immersed in an aqueous solution of a nucleophilic sulfonating agent such as sulfite as a sulfonating agent, and the halogeno groups of the halomethyl groups are converted to sulfonic acid groups as shown in the following reaction formula: N The sulfonic acid groups can be substituted by two mechanisms. In this case, it is thought that sulfonic acid groups are preferentially introduced onto the outer surface of the support membrane, but it is also possible that the inner surface of the membrane, i.e., the pore surface, may also be sulfonated. However, since it is thought that the PPO inside the support membrane is substantially not sulfonated or is hardly sulfonated at all, it is possible to sulfonate the membrane surface without reducing the mechanical strength of the entire support membrane. Furthermore, although it is thought that sulfonic acid groups are mainly introduced by using sulfite, the possibility of sulfate groups being introduced cannot be denied.

[0045]

[0046] Examples of sulfites that can be used include sodium sulfite and potassium sulfite. The concentration of the sulfite aqueous solution can be 5% by mass or more, preferably 10% by mass or more. The reaction temperature is preferably from room temperature to less than 100°C. The higher the reaction temperature, the more accelerated the sulfonation reaction tends to be. The reaction time can be selected in appropriate combination with the reaction temperature. It is also preferable to add an appropriate amount of a phase transfer catalyst to the reaction solution, as this accelerates the sulfonation reaction on the support membrane surface. The phase transfer catalyst is not particularly limited, but examples include quaternary ammonium salts, phosphonium salts, polyethylene glycol, crown ethers, etc., and tetrabutylammonium bromide (TBAB) is preferred.

[0047] When sulfonating agents such as sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, and sulfur trioxide are used, it is believed that the benzene ring of PPO is primarily directly sulfonated, but there is also a possibility that the benzyl position may also be sulfonated. Furthermore, when PPO in which a hydroxyl group or a hydroxymethyl group is substituted on the benzene ring is used as the raw material PPO, it is believed that a sulfate group is introduced at the benzyl position. An example of a structural unit of a sulfonated modified PPO is shown below.

[0048]

[0049] [In the formula, R 11 ~R 14 R independently represents a sulfonic acid group, a sulfate group, or H; 11 and / or R 12 represents a sulfonic acid group or a sulfate group on a benzene ring, R 13 and / or R 14 represents a sulfonic acid group or a sulfate group at the benzyl position, R 11 ~R 14 At least one of the groups is a sulfonic acid group or a sulfate group.]

[0050] After the reaction, a typical post-treatment can be performed. For example, the sulfonating agent can be removed by thoroughly washing the sulfonated support membrane with water. The support membrane essentially consists of sulfonated modified PPO. "Consisting of sulfonated modified PPO" means that the support membrane does not intentionally contain any components other than sulfonated modified PPO, although it may contain unintended residual components such as solvents, pore-forming agents, and sulfonating agents, or unintended contaminants.

[0051] The thickness of the support film is preferably 10 μm or more and 100 μm or less. If the support film thickness is 10 μm or more, sufficient mechanical strength can be ensured and the generation of defects can be more reliably suppressed. On the other hand, if the support film thickness is 100 μm or less, the permeation resistance can be sufficiently reduced.

[0052] 3. Separation Functional Layer Formation Step In this step, the sulfonated support membrane produced in step 2 is contacted with an aqueous solution containing a cationic polymer to form a cationic polymer layer on the sulfonated support membrane, which functions as a separation functional layer. The support membrane produced in the previous step, at least the surface of which has been sulfonated, has a strong negative potential surface due to sulfonic acid groups / sulfate groups, and at the same time, is highly hydrophilic. Therefore, by contacting the sulfonated support membrane with an aqueous solution containing a cationic polymer, a cationic polymer layer that functions as a separation functional layer can be successfully formed on the sulfonated support membrane (Figure 1).

[0053] The cationic polymer is not particularly limited as long as it has cationic groups and can be adsorbed to the surface of a support membrane having anionic groups, such as sulfonic acid groups / sulfuric acid groups, on at least its surface by ion exchange reaction and electrostatic bonding to form a layer, and examples thereof include polyethyleneimine, polyallylamine, polyvinylamine, and cationic polyvinyl alcohol. From the viewpoint of forming a chemically stable and defect-free thin film and obtaining high permeation selectivity in an organic solvent system, it is particularly preferable to use cationic polyvinyl alcohol containing quaternary ammonium groups.

[0054] The concentration of the cationic polymer in the aqueous solution may be adjusted as appropriate within a range that allows a good formation of a cationic polymer layer on the support membrane, and may be adjusted to, for example, 0.01% by mass or more and less than 1% by mass. It is also preferable to adjust the ionic strength by adding an inorganic salt to the aqueous solution depending on the charge density and degree of ionic dissociation of the cationic polymer.

[0055] The conditions for forming the cationic polymer layer may be adjusted as appropriate, for example, by immersing the support membrane in an aqueous solution of the cationic polymer. The temperature during immersion is not particularly limited, but room temperature is sufficient because the cationic polymer is adsorbed onto the support membrane surface by ion exchange reaction and electrostatic bonding. The immersion time may also be adjusted as appropriate, for example, from 1 minute to 10 hours.

[0056] After forming a cationic polymer layer on the support membrane, a known layer-by-layer adsorption method (LbL method: Layer-by-Layer method) may be used to alternately adsorb an optional anionic polymer layer or betaine polymer layer and a cationic polymer layer multiple times.

[0057] It is believed that when the support membrane is immersed in an aqueous solution of a cationic polymer, the cationic polymer in the solution is adsorbed to the anionic sulfonic acid groups / sulfonic acid groups present on the surface of the support membrane through ion exchange reactions and electrostatic bonding. Therefore, after the cationic polymer layer is formed, the support membrane with the cationic polymer layer formed on its surface can be removed from the aqueous solution. The support membrane with the cationic polymer layer formed on it can be washed with water or dried.

[0058] The thickness of the cationic polymer layer may be adjusted as appropriate, and may be, for example, 1 nm or more and 100 nm or less. The thickness is preferably 5 nm or more, more preferably 10 nm or more, and preferably 50 nm or less, more preferably 30 nm or less. The cationic polymer layer should be formed by ion exchange reaction and electrostatic bonding, and there is no particular need to confirm its formation. However, if necessary, the amount of adsorption of the cationic polymer can be calculated from the difference in the concentration of the cationic polymer in the aqueous solution before and after immersion of the support membrane in the cationic polymer aqueous solution.

[0059] 4. Step of Crosslinking Cationic Polymer In this step, the cationic polymer in the cationic polymer layer formed on the support membrane is crosslinked to insolubilize the cationic polymer and immobilize the cationic polymer layer on the support membrane (FIG. 1).

[0060] The crosslinking agent for crosslinking the cationic polymer is not particularly limited as long as it can react with two or more active groups, such as amino groups or hydroxyl groups, possessed by the cationic polymer to effect intramolecular or intermolecular crosslinking. Examples of the crosslinking agent include aldehyde-type crosslinking agents such as glutaraldehyde, formaldehyde, glyoxal, and succinaldehyde; epoxy-type crosslinking agents having two or more epoxy groups; and N-methylol-type crosslinking agents such as dimethylol urea, trimethylol melamine, dimethylol ethylene urea, hexamethylol melamine, and dimethylol propylene urea, and glutaraldehyde can be preferably used.

[0061] The crosslinking conditions of the cationic polymer can be adjusted as appropriate. For example, a composite film of a support film and a cationic polymer layer can be immersed in a solution of a crosslinking agent. The solvent for the crosslinking agent solution can be selected as appropriate depending on the crosslinking agent used, and water can be used, for example. The concentration of the crosslinking agent solution can be adjusted as appropriate, and can be, for example, 0.1% by mass or more and 10% by mass or less. The temperature during immersion is not particularly limited and can be adjusted as appropriate depending on the crosslinking agent used, and can be adjusted, for example, within a range of 20°C or more and the boiling point of the solvent or less. Crosslinking can also be performed under heated reflux conditions of the solvent. The crosslinking time can also be adjusted as appropriate, and can be, for example, 30 minutes or more and 50 hours or less.

[0062] Note that this step 4, i.e., crosslinking of the cationic polymer, may be carried out after the separation functional layer formation step 3, or may be carried out simultaneously with the separation functional layer formation step 3. When the steps 3 and this step 4 are carried out simultaneously, a crosslinking agent may be mixed into the aqueous cationic polymer solution described in step 3, and the reaction temperature and reaction time may be adjusted so that the formation of the cationic polymer layer on the support membrane and crosslinking occur simultaneously. In addition, a rinsing treatment with pure water or the like may be inserted between the steps 3 and 4.

[0063] 5. Polar Group Introduction Process In this process, polar groups are introduced into the sulfonated modified PPO in the support membrane in addition to the sulfonic acid groups / sulfuric acid groups. It is difficult to introduce sulfonic acid groups / sulfuric acid groups to a degree that sufficiently improves the solvent resistance of the PPO by simply sulfonating the PPO. Therefore, according to the present invention, by introducing polar groups in addition to the sulfonic acid groups / sulfuric acid groups, it is possible to further improve the solvent resistance of the entire PPO ( FIG. 1 ).

[0064] This step 5 can be carried out after the sulfonic acid group / sulfuric acid group introduction step 2. That is, by introducing polar groups after sulfonating the PPO in the support membrane, the solvent resistance of the PPO can be improved without inhibiting the introduction of sulfonic acid groups / sulfuric acid groups.

[0065] Furthermore, this step 5 may be carried out after the cationic polymer crosslinking step 4, or may be carried out between the sulfonic acid group / sulfuric acid group introduction step 2 and the separation functional layer formation step 3, or between the separation functional layer formation step 3 and the cationic polymer crosslinking step 4. That is, polar groups in addition to sulfonic acid groups / sulfuric acid groups may be introduced into the support membrane, and then a cationic polymer layer may be formed on the support membrane; hydrophilicity may be introduced into the support membrane after forming a cationic polymer layer on a sulfonated support membrane, and then the cationic polymer may be crosslinked; or polar groups may be introduced into the support membrane after crosslinking the cationic polymer layer on the support membrane.

[0066] A polar group is a group that has polarity due to having a lone electron pair or being polarized within the group, and therefore confers insolubility and resistance to non-polar organic solvents and low-polarity organic solvents. The polar group is not particularly limited as long as it is a group other than a sulfonic acid group or a sulfate group and has such an effect, but examples thereof include monovalent polar groups such as a hydroxyl group, -NH2, and a carboxy group; an ether group (-O-), a thioether group (-S-), a sulfinyl group (-S(=O)-), a sulfonyl group (-S(=O)2-), a carbonyl group, and -NR 9 - (wherein, R 9 is H or C 1-6and divalent polar groups such as a hydroxyl group, an ether group, a sulfonyl group, and —NR 9 - is preferably one or more polar groups selected from. For example, the monovalent polar group is covalently bonded to the unit structure of the modified polyphenylene oxide directly or indirectly via a linker group, and the divalent polar group may crosslink two unit structures within one molecule of the modified polyphenylene oxide, or may crosslink two molecules, either alone or via a linker group described below. In the present disclosure, for convenience, sulfonic acid groups / sulfuric acid groups are not included in the polar group.

[0067] The polar group and the sulfonic acid group / sulfuric acid group may be bonded to the benzene ring of PPO via a linker group. The linker group increases the spatial freedom of the polar group and facilitates the introduction of the polar group into PPO. The linker group is not particularly limited as long as it has the above-mentioned effect, but examples thereof include C 1-6 Alkylene group, divalent C 6-12 Examples include aromatic hydrocarbon groups, ester groups (-O-C(=O)- or -C(=O)-O-), amide groups (-NH-C(=O)- or -C(=O)-NH-), urea groups (-NH-C(=O)-NH-), thiourea groups (-NH-C(=S)-NH-), and groups in which 2 or more and 5 or less of these groups are linked together.

[0068] Polar groups can be introduced into modified PPO by conventional methods. For example, in the case of modified PPO having halomethyl groups, it is preferable to immerse the modified PPO in a solution of a nucleophilic agent containing a polar group, thereby substituting the nucleophilic agent for the halogen atoms at the remaining benzyl positions in the support membrane that have not been sulfonated, thereby introducing polar groups and imparting resistance to organic solvents. Examples of nucleophilic agents for introducing polar groups include amines, phenolates, and sulfinates. Examples of amines that can be used include monofunctional amines, bifunctional amines, and polyfunctional amines. Preferably, monofunctional amines with small molecular weights are used in order to sufficiently penetrate into the membrane and increase resistance to organic solvents, and monoethanolamine represented by the following formula (IV) is preferred.

[0069] [In the formula, R21 is H or C 1-6 represents an alkyl group.]

[0070] For example, modified PPO having halomethyl groups reacts with monoethanolamine (IV) as shown in the following formula: This polymer structure has excellent hydrogen bonding properties, resulting in excellent hydrophilicity and extremely high organic solvent resistance. It also has good resistance under acidic and alkaline conditions.

[0071]

[0072] As the phenolate, a difunctional or trifunctional phenol is preferably used, which converts the phenolic hydroxyl group into a highly nucleophilic phenoxide ion in an organic solvent to which a base has been added, resulting in substitution at the benzyl position and a crosslinking reaction. The phenol can be selected from resorcinol, hydroquinone, phloroglucinol, bisphenols, etc. From the viewpoint of enhancing permeability into the membrane interior and crosslinking reactivity, hydroquinone and phloroglucinol are particularly preferred. As the base, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal carbonates such as potassium carbonate are preferred. Since phenols are susceptible to oxidation in air, the reaction is preferably carried out in an inert gas such as nitrogen or argon. For example, when hydroquinone is used, a crosslinked structure as shown in the following formula can be formed between the benzene units of the modified PPO. This structure has excellent resistance to acid and alkaline conditions. While the crosslinking is considered to be primarily intermolecular crosslinking, intramolecular crosslinking is also possible.

[0073]

[0074] Hydroxymethanesulfinic acid sodium salt can be preferably used as the sulfinate. Hydroxymethanesulfinic acid is known to undergo a reaction between two benzyl halide compounds, forming a sulfone bond while releasing formaldehyde. Specifically, as shown in the reaction formula below, a membrane structure with organic solvent resistance can be obtained in which the benzyl positions of the modified PPO are crosslinked with a sulfone bond. Because sulfone bonds are highly electron-withdrawing functional groups, PPO membranes highly crosslinked with sulfinates exhibit a significant decrease in the electron density of the main chain benzene ring, which is expected to improve resistance to oxidizing conditions such as radicals in addition to resistance to acid and alkaline conditions. Note that while the crosslinking is thought to be primarily intermolecular crosslinking, intramolecular crosslinking is also possible.

[0075]

[0076] The concentration of the nucleophile in the reaction between the amine, phenolate, or sulfinate and the modified PPO support membrane may be adjusted as appropriate, but may be, for example, 1% by mass or more and 10% by mass or less. Furthermore, from the viewpoint of improving reaction efficiency and permeability into the bulk of the membrane, it is preferable to select an organic solvent other than water that does not dissolve the modified PPO. For example, alcohol solvents such as methanol and ethanol; nitrile solvents such as acetonitrile; sulfoxide solvents such as dimethyl sulfoxide; and mixtures of these solvents may be used. Reaction conditions such as reaction temperature and reaction time may be appropriately set in consideration of the reactivity of the nucleophile.

[0077] The composite separation membrane of the present invention is an asymmetric membrane having an asymmetric structure, which has a support membrane made of modified polyphenylene oxide and a separation functional layer made of cross-linked cationic polymer, characterized in that the modified polyphenylene oxide has sulfonic acid groups / sulfuric acid groups and polar groups, and the separation functional layer is formed on the support membrane.

[0078] The composite separation membrane according to the present invention, particularly due to the separation functional layer, has high separation performance for insoluble substances such as microorganisms, insoluble particles, and polymers; relatively large solutes such as amino acids; ions such as monovalent ions, polyvalent ions, cations, and anions; and neutral substances. The pore size and porosity of the composite separation membrane according to the present invention can be adjusted according to the substance to be separated, and can be adjusted by the concentration of the PPO solution, the amount of PPO solution applied to the substrate, the basis weight of the substrate, the pore size of the substrate, the amount of pore-forming agent, etc.

[0079] To separate a substance to be separated from a liquid to be treated, the liquid to be treated may be passed through the composite separation membrane of the present invention. The composite separation membrane of the present invention has polar groups in addition to sulfonic acid groups and sulfate groups, and therefore exhibits excellent organic solvent resistance and can be used to treat liquids containing organic solvents. Therefore, it can be suitably used, for example, as a liquid treatment membrane or a gas treatment membrane, and particularly as a microfiltration membrane, ultrafiltration membrane, nanofiltration membrane, osmosis membrane, reverse osmosis membrane, gas separation membrane, etc.

[0080] The composite separation membrane according to the present invention exhibits excellent organic solvent resistance and is therefore capable of treating a liquid to be treated that contains an organic solvent. The organic solvent that may be contained in the liquid to be treated is not particularly limited, and examples thereof include alcohol solvents such as methanol, ethanol, 2-propanol, cyclohexanol, and propylene glycol monoethyl ether; polyhydric alcohol solvents such as ethylene glycol, propylene glycol, and glycerin; ether solvents such as diethyl ether, t-butyl methyl ether, tetrahydrofuran, dioxane, and diethylene glycol dimethyl ether; organic acid solvents such as formic acid and acetic acid; nitrile solvents such as acetonitrile; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and ethyl lactate; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; aromatic hydrocarbon solvents such as benzene, toluene, and chlorobenzene; halogenated hydrocarbon solvents such as dichloroethane, chloroform, and carbon tetrachloride; amide solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfoxide solvents such as dimethyl sulfoxide.

[0081] This application claims the benefit of priority based on Japanese Patent Application No. 2024-000080, filed on January 4, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-000080, filed on January 4, 2024, are incorporated herein by reference.

[0082] The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course possible to carry out the invention by making appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention.

[0083] Example 1 (1) Synthesis of brominated polyphenylene oxide 40 g of poly(2,6-dimethyl-1,4-phenylene oxide) ("181781" manufactured by Sigma-Aldrich) was charged into a 500 mL four-neck flask equipped with a reflux condenser, a nitrogen inlet, and a stirring blade. 240 mL of chlorobenzene was added and dissolved under nitrogen purging. When a homogeneous, transparent solution was obtained, 107 g of N-bromosuccinimide and 2.0 g of azobisisobutyronitrile as a radical initiator were added. With vigorous stirring, the reaction solution was heated to 120°C using an oil bath while monitoring the heating rate, and the reaction was carried out at 120°C for 6.5 hours. After allowing the reaction solution to cool, 2 L of methanol was added, and the precipitated flaky polymer was finely crushed in a blender. The polymer was then thoroughly washed, with the methanol being renewed. The polymer was then vacuum-dried at 60°C to obtain powdered brominated polyphenylene oxide (BrPPO). NMR analysis of the resulting BrPPO revealed that the degree of bromination at the benzyl position was 1.46 and the degree of bromination at the benzene ring was 0.22.

[0084] (2) Preparation of BrPPO film N-methyl-2-pyrrolidone and polyethylene glycol (PEG400) with a molecular weight of 400 were added to BrPPO and the mixture was kneaded and dissolved at 60°C for 6 hours to prepare a film-forming solution with a BrPPO concentration of 30% by mass. The resulting film-forming solution was degassed under reduced pressure, then applied with a doctor blade to a polyphenylene sulfide (PPS) nonwoven fabric with a width of 300 mm and a thickness of 120 μm, and coagulated in a water bath at 25°C for 10 minutes. The coagulated film was thoroughly washed with water and then air-dried to obtain a BrPPO film. The film was cut into a circle with a diameter of 48 mm. The resulting film was immersed in a 13% by mass aqueous solution of sodium sulfite at 98°C for 30 minutes. After the reaction was completed, the film was thoroughly washed with water. Hereinafter, the film in this state will be referred to as support film A. When the elemental composition of the film surface was evaluated by XPS, the sulfur ratio was found to be 1.6%.

[0085] (3) Formation of Separation Functional Layer A copolymer of diallyldimethylammonium chloride and vinyl acetate was completely saponified to synthesize cationic polyvinyl alcohol (CPVA) having the following structural units: The weight-average molecular weight of the CPVA was 64,000, and the molar fraction of the cationic monomer was 1.5 mol%. CPVA was dissolved in pure water to prepare an aqueous solution with a CPVA concentration of 1000 mg / L. This solution was brought into contact with the outer surface of support membrane A at room temperature for 20 minutes to form a CPVA adsorption layer. Then, support membrane A was impregnated with a 1% by mass aqueous solution of glutaraldehyde and crosslinked at 80° C. for 24 hours. The resulting membrane was then thoroughly washed with water to obtain composite membrane B.

[0086] (4) Introduction of polar groups Composite membrane B was immersed in a 3 vol% methanol solution of monoethanolamine (MEA) at room temperature for 24 hours to replace the remaining unsulfonated benzyl bromine in support membrane A with MEA. After the reaction was completed, the resulting membrane was washed with methanol to obtain composite membrane C. In addition, to confirm the introduction of the polar group MEA, MEA was introduced into sulfonated support membrane A without a separation functional layer under the same conditions to prepare an MEA-introduced support membrane.

[0087] Example 2 Support membrane A, composite membrane B, and composite membrane C were obtained in the same manner as in Example 1 (2), except that the sulfonation reaction time was changed from 30 minutes to 5 minutes. The sulfur content of support membrane A was 1.1%, and the sulfur content decreased slightly due to the shortening of the sulfonation reaction time.

[0088] Example 3 Support membrane A, composite membrane B, and composite membrane C were obtained in the same manner as in Example 1 (2), except that in Example 1 (2), 0.15 M tetrabutylammonium bromide (TBAB) was added to a 10 mass % aqueous sodium sulfite solution and the reaction temperature was changed from 98° C. to 80° C. The sulfur ratio of support membrane A was 4.3%, and the use of a phase transfer catalyst improved the sulfonation efficiency.

[0089] Example 4 In Example 1 (4), a 2 mass% acetonitrile / dimethyl sulfoxide mixed solution of hydroquinone (HQ) was used as the nucleophile instead of a 3 vol% methanol solution of MEA, an equimolar amount of potassium carbonate was added relative to the phenolic hydroxyl groups of HQ, and the composite membrane B was immersed in a nitrogen atmosphere at 60°C for 24 hours. In the same manner as in Example 1, a support membrane A, a composite membrane B, and a composite membrane C were obtained.

[0090] Example 5 In Example 1 (4), a support membrane A, a composite membrane B, and a composite membrane C were obtained in the same manner as in Example 1, except that in Example 1 (4), a 2 mass% acetonitrile / dimethyl sulfoxide mixed solution of phloroglucinol (PG) was used as the nucleophile instead of a 3 vol% methanol solution of MEA, an equimolar amount of potassium carbonate was added relative to the phenolic hydroxyl groups of PG, and the composite membrane B was immersed at 60°C for 24 hours under a nitrogen atmosphere.

[0091] Example 6 A support membrane A, a composite membrane B, and a composite membrane C in which benzyl groups of the BrPPO membrane were crosslinked with sulfonyl groups (—SO—) were obtained in the same manner as in Example 1 (4), except that in Example 1 (4), a 2 mass % methanol solution of sodium hydroxymethanesulfinate dihydrate (HMS-Na) and a dimethyl sulfoxide solution were used as the nucleophilic agent instead of a 3 vol % methanol solution of MEA, and the composite membrane was successively immersed in the methanol solution and the dimethyl sulfoxide solution at 40° C. for 12 hours each.

[0092] Example 7 In Example 1 (3), polyethyleneimine (PEI, "Epomin (registered trademark) P-1000" manufactured by Nippon Shokubai Co., Ltd., molecular weight: 70,000) was used as the cationic polymer, and an aqueous solution was prepared in 0.5 M NaCl aqueous solution so that the PEI concentration was 1,000 mg / L. The pH was adjusted and the solution was brought into contact with the surface of support membrane A for 20 minutes. After that, the membrane was immersed in a 0.3 mass % GA aqueous solution at room temperature for 1 hour for crosslinking, and the procedure was the same as in Example 1 to obtain support membrane A, composite membrane B, and composite membrane C.

[0093] Example 8 In Example 1 (3), a support membrane A, a composite membrane B, and a composite membrane C were obtained in the same manner as in Example 1, except that in Example 1 (3), polyallylamine (PAA, "PAA-HCL-10L" manufactured by Nittobo Medical, molecular weight: 100,000) was used as the cationic polymer, and an aqueous solution was prepared in a 0.5 M NaCl aqueous solution so that the PAA concentration was 1,000 mg / L. The pH was adjusted and the solution was brought into contact with the surface of support membrane A for 20 minutes, and then the membrane was immersed in a 0.3 mass % GA aqueous solution at room temperature for 1 hour for crosslinking.

[0094] Comparative Example 1 Composite membranes B and C were prepared in the same manner as in Example 1(2), except that the support membrane was not sulfonated.

[0095] Comparative Example 2 Composite membrane B was prepared in the same manner as in Example 1 (1) to (3).

[0096] Test Example 1: Elemental Composition The elemental compositions of the BrPPO membrane of Example 1, the sulfonated support membrane A, and the support membrane without a separation functional layer and subjected to sulfonation and MEA introduction were analyzed by X-ray photoelectron spectroscopy (XPS). The apparatus and measurement conditions used for the XPS analysis are as follows: Apparatus: K-Alpha+ (manufactured by Thermo Fisher Scientific) Excitation X-ray: Monochromatized Al Kα ray X-ray output: 12 kV, 2.5 mA Photoelectron escape angle: 90° Spot size: Approximately 200 μmφ Pass energy: 50 eV Step: 0.1 eV The analysis results are shown in Table 1, along with the calculated elemental composition of the BrPPO membrane. The calculated values ​​are based on the NMR analysis results of the BrPPO film, which show a degree of bromination at the benzyl position of 1.46 and a degree of bromination at the benzene nucleus of 0.22.

[0097]

[0098] As shown in Table 1, after sulfonation with sodium sulfite, the ratio of bromine element decreased slightly, and the ratios of sulfur, sodium, and oxygen increased, suggesting the introduction of sulfonic acid groups. Furthermore, when sulfonated support membrane A was immersed in a strongly basic MEA / methanol solution for 24 hours and then subjected to XPS analysis, the ratio of bromine element decreased significantly, and the amount of nitrogen element derived from MEA increased. The ratio of sulfur element remained almost unchanged, suggesting that MEA was introduced while the sulfonic acid groups were largely maintained without being released.

[0099] Figures 2(1) and 2(2) show the relationship between reaction temperature, sulfur content, and bromine content when the reaction time is fixed at 30 minutes and a phase transfer catalyst (TBAB) is used and when it is not used. Figure 2(3) shows the relationship between reaction time and sulfur content (left axis) and bromine content (right axis) when the reaction temperature is fixed at 98°C and a phase transfer catalyst (TBAB) is not used. As shown in Figures 2(1) and 2(2), it was revealed that the use of a phase transfer catalyst promotes the substitution reaction of bromo groups from bromomethyl groups with sulfonic acid groups. Furthermore, Figure 2(3) shows that bromo groups are replaced with sulfonic acid groups as the reaction progresses.

[0100] Test Example 2: Infrared absorption spectroscopy The BrPPO membrane having a bromomethyl group, the sulfonated support membrane A, and the support membrane without a separation functional layer, which had been sulfonated and had an MEA introduced therein, were analyzed by infrared absorption spectroscopy under the following conditions. The results are shown in Figure 3. Apparatus: "Cary 670 FTIR" manufactured by Agilent Technologies. Accessory: "Single reflection Ge ATR accessory Foundation Thunder Dome" manufactured by Spectra-Tech. Incident angle: 45°. Resolution: 4 cm. -1 Number of times accumulated: 64

[0101] As shown in Figure 3(1), the MEA-introduced support membrane has a peak temperature of 2800 to 3000 cm -1 and 3,400 cm -1 Peaks are observed around . These peaks are thought to be derived from the methylene group and hydroxyl group of MEA, respectively. Furthermore, as shown in Figure 3 (2), a peak derived from -SO3H is observed in support membrane A compared to the BrPPO membrane. A shoulder, which is thought to be a peak derived from -SO3H, is also observed in the sulfonated-MEA-introduced support membrane. However, it is thought that peaks derived from the C-N bond of MEA also overlap.

[0102] Test Example 3: Organic Solvent Resistance Test The sulfonated BrPPO membrane of Example 1(2) and the composite membrane C of Example 1(4) were cut into 1 cm squares and immersed in water or each organic solvent shown in Table 2 for 24 hours at room temperature or heated to 100°C on a hot plate to evaluate the solvent resistance of the membranes. For solvents with boiling points below 100°C, the evaluation was performed at a temperature set 10°C lower than the boiling point. The results are shown in Table 2. In the table, "NS" indicates complete insolubility, "PS" indicates solubility at high temperatures, and "GS" indicates solubility even at room temperature.

[0103]

[0104] As shown in Table 2, the polyphenylene oxide membrane with bromomethyl groups introduced was insoluble in relatively polar organic solvents, but was soluble at room temperature in organic solvents with three Hansen solubility parameters similar to each other, such as toluene and chlorobenzene. In contrast, composite membrane C of the present invention, which was laminated with a crosslinked cationic polymer layer and had polar groups introduced, was insoluble in all solvents tested. This demonstrates that the composite membrane of the present invention exhibits sufficient durability against organic solvents.

[0105] Test Example 4: Separation test of sulfonated BrPPO membrane (support membrane A) in aqueous system The separation performance in aqueous system of each support membrane A sufficiently wetted with water and composite membrane B before the introduction of polar groups was evaluated using a cross-flow type flat membrane evaluation device consisting of a stainless steel pressure vessel, a supply water tank and a pump. The pure water permeability (Permeance) was L p It is expressed as: L p was calculated using the following formula by conducting a permeation test on the membrane sample using pure water at a pressure of 15 bar. p [L / (m 2 ・h・bar)] = permeated pure water amount [L] / (membrane area [m 2 ] × sampling time [h] × measurement pressure [bar])

[0106] The rejection rate of sodium chloride (NaCl) was calculated by feeding an aqueous solution prepared to a concentration of 1500 mg / L at a temperature of 25°C and a pressure of 15 bar for 1 hour, measuring the conductivity of the membrane permeate water and the feed water using an electric conductivity meter (CM-25R, manufactured by DKK-TOA Corporation), and using the following formula: NaCl rejection rate [%] = (1 - membrane permeate water conductivity [μS / cm] / feed aqueous solution conductivity [μS / m]) × 100

[0107] The neutral molecule rejection rate of an aqueous system was evaluated using sucrose (manufactured by Nacalai Tesque, molecular weight 342.3). A 200 mg / L aqueous sucrose solution was supplied to the cross-flow flat membrane evaluation device at 25°C and a pressure of 15 bar for 1 hour, and then the permeated water was sampled and the feed solution concentration and permeated solution concentration were measured using a total organic carbon analyzer ("ON-LINE TOC-VCSH" manufactured by Shimadzu Corporation). The sucrose rejection rate was calculated using the following formula: Sucrose rejection rate [%] = 100 × [1 - (permeated solution concentration) / (feed solution concentration)]

[0108]

[0109] In Table 3, the support membrane of Comparative Example 1 was not sulfonated, and the data for support membrane A of Comparative Example 1 are data for a non-sulfonated support membrane. The non-sulfonated support membrane had excellent pure water permeability, but was completely unable to block the permeation of NaCl. Based on these experimental results, the sucrose rejection rate of the support membrane of Comparative Example 1 was not measured. Furthermore, composite membrane B of Comparative Example 1 had a very high pure water permeability, but was almost unable to block the permeation of NaCl and sucrose. One possible reason for this is that, because the support membrane was not sulfonated, adhesion between the support membrane and the crosslinked cationic polymer was low, resulting in separation of the crosslinked cationic polymer from the support membrane.

[0110] In contrast, the composite membranes B of Examples 1 to 8 had excellent molecular rejection ability. The reason why the composite membranes B of Examples 3, 7, and 8 had high pure water permeability is thought to be that in Example 3, a phase transfer catalyst was used to sulfonate the support membrane A, resulting in the introduction of many sulfonic acid groups, and in Examples 7 and 8, a cationic polymer not containing vinyl alcohol units was used, resulting in high hydrophilicity of the composite membrane. Consequently, the molecular rejection rate was relatively low. The reason why the pure water permeability and molecular rejection rate of Comparative Example 2 were equivalent to those of the Examples is that, at the stage of composite membrane B, polar groups, a feature of the present invention, had not yet been introduced.

[0111] Test Example 5: Permeability test of composite membrane in organic solvent system Acetonitrile, N-methyl-2-pyrrolidone, and toluene were used as organic solvents. A membrane sample thoroughly wetted with each organic solvent was placed in a stainless steel pressure vessel sealed with a sealant made by FFKM, and the organic solvent was transferred from a 500 mL HPLC screw-cap bottle to the pressure vessel using an HPLC preparative pump to evaluate the permeability. At the beginning of the separation evaluation, each pure solvent was supplied at a pressure of 15 bar, and the permeability L p was calculated using the following formula: p [L / (m 2 ・h ・bar)] = permeate volume [L] / membrane area [m 2 ] / sampling time [h] / measurement pressure [bar]

[0112] Diol-type polypropylene glycol (PPG1000) with a molecular weight of 1000 (manufactured by Fujifilm Wako) was used as a marker for separation tests in organic solvent systems. A 400 mg / L PPG1000 solution was supplied at a temperature of 25°C and a pressure of 15 bar. After 6 hours of stabilization operation, the permeated liquid was collected from the membrane. Peak analysis of PPG1000 in the feed liquid and permeated liquid was performed using high-performance liquid chromatography (HPLC) equipped with a corona charge detector, and the rejection rate of PPG1000 was calculated from the area ratio of the molecular weight components located at the peak top before and after permeation. For sample solutions in separation tests using toluene solvent, the toluene was completely evaporated once, and an equal volume of ethanol was added and thoroughly stirred, followed by HPLC evaluation. Rejection rate [%] = 100 x [1 - (peak area of ​​the peak top molecular weight component in the permeated liquid) / (peak area of ​​the peak top molecular weight component in the feed liquid)]

[0113] The HPLC measurement conditions are as follows: Apparatus: Thermo Fisher Scientific Vanquish Column: Waters BEH C18 2.1 x 150 mm Mobile phase: A. Ultrapure water, B. Acetonitrile 0 to 15 min - 5% B in A 15 to 20 min - 60% B in A 20 to 25 min - 100% B Flow rate: 0.25 mL / min Column temperature: 40°C Injection volume: 5 μL Detection: Charged aerosol detector (CAD) Drying tube temperature: 35°C

[0114]

[0115] As shown in Table 4, the molecular rejection ability of the composite separation membrane of Comparative Example 1 was insufficient. The reason for this is thought to be that the support membrane was not sulfonated, so the cationic polymer did not adsorb, and the separation function layer was not sufficiently formed. In other words, the membrane of Comparative Example 1 essentially corresponds to a support membrane made of modified PPO solvent-resistant, and because the membrane is highly polar due to monoethanolamine, filtration in organic solvents is possible, and it is thought to have exhibited separation performance, albeit insufficient. Composite membrane B of Comparative Example 2, in which no polar groups were introduced, swelled or dissolved in the three organic solvents tested, demonstrating that it was completely useless as a separation membrane in organic solvent systems. In contrast, on support membrane A of the example in which sulfonic acid groups were introduced into polyphenylene oxide via methylene groups according to the present invention, a cationic polymer layer functioning as a separation function layer could be effectively formed, and because it exhibited high insolubility in organic solvents, it demonstrated excellent separation performance in both aqueous and organic solvent systems.

Claims

1. A composite separation membrane having a support membrane made of a modified polyphenylene oxide and a separation functional layer made of a crosslinked cationic polymer, wherein the modified polyphenylene oxide has a sulfonic acid group and / or a sulfuric acid group and a polar group, and the separation functional layer is formed on the support membrane.

2. The composite separation membrane according to claim 1, wherein the sulfonic acid group and / or the sulfuric acid group and the polar group are introduced into the benzene ring of the modified polyphenylene oxide via a linker group.

3. The composite separation membrane according to claim 2, wherein the benzene ring of the modified polyphenylene oxide has a methyl sulfonate group.

4. The composite separation membrane according to claim 1, wherein the polar group is one or more polar groups selected from a hydroxyl group, an ether group, a sulfonyl group, and an amino group.

5. The composite separation membrane according to claim 1, wherein the cationic polymer is a cationic polyvinyl alcohol copolymer containing a structural unit having a quaternary ammonium cation group.

6. The composite separation membrane according to claim 1, wherein the cationic polymer is one or more polyamines selected from polyethyleneimine, polyvinylamine, and polyallylamine.

7. A method for producing a composite separation membrane, comprising: obtaining a support membrane using polyphenylene oxide; introducing a sulfonic acid group and / or a sulfuric acid group into the support membrane by contacting the support membrane with a sulfonating agent; contacting the support membrane having the sulfonic acid group and / or the sulfuric acid group introduced thereinto with an aqueous solution containing a cationic polymer to form a cationic polymer layer on the support membrane; crosslinking the cationic polymer in the cationic polymer layer; and introducing a polar group into the polyphenylene oxide in the support membrane.

8. The method according to claim 7, wherein a support membrane made of the polyphenylene oxide having a halomethyl group introduced into the benzene ring is contacted with an aqueous solution containing a sulfite as the sulfonating agent to introduce the sulfonic acid group into the halomethyl group.

9. The method according to claim 7, wherein the polar group is introduced by reacting the polyphenylene oxide having a halomethyl group introduced into the benzene ring with monoethanolamine represented by the following formula (IV). [In the formula, R 21 represents H or C 1-6 alkyl group. ]

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