Modified polyphenyleneoxide separation membrane and method for producing same

Abstract

The purpose of the present invention is to provide a separation membrane having excellent organic solvent resistance, acid resistance, and base resistance. The present invention pertains to a modified polyphenyleneoxide separation membrane obtained by substituting, in a polyphenyleneoxide precursor film in which at least a portion of benzyl positions at position 2 and position 6 are halogenated, at least a portion of the halogens with an alkanolamine. The present invention also pertains to a method for producing a modified polyphenyleneoxide separation membrane, the method comprising immersing a precursor film made of a halogenated polyphenyleneoxide in which at least a portion of benzyl positions at position 2 and position 6 are halogenated, in a reaction solution containing an alkanolamine dissolved in an organic solvent in which the precursor film will not be dissolved, to substitute at least a portion of halogens at the benzyl positions with an alkanolamine.

Description

Modified polyphenylene oxide separation membrane and its manufacturing method

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

[0002] Compared to distillation, membrane separation has the advantage of significantly reducing the energy required for separation because it does not involve phase inversion. 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 applied in a wide range of industrial fields, including seawater desalination, drinking water treatment, sewage treatment, and blood purification membranes. However, the medium used in conventional membrane separation is often water.

[0003] In industrial fields such as 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 are posing social issues.

[0004] In order to apply membrane separation methods to separation processes using organic solvents as a medium, such as purification by fractionation of low molecular weight substances or fractionation and purification of the organic solvent itself, it is necessary to develop nanofiltration membranes and reverse osmosis membranes that can perform stable filtration operations in organic solvents for long periods of time.

[0005] Separation membranes made of polyphenylene oxide (PPO) or its derivatives are relatively inexpensive and have high mechanical strength, alkali resistance, and acid resistance. Furthermore, because they are resistant to aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), they are thought to have excellent potential as membrane materials applicable to filtration processes using these pure solvents as media, as well as organic solvent filtration processes containing alkalis or acids.

[0006] For example, Patent Document 1 discloses a method for producing a separation membrane and a composite membrane using PPO, and states that this membrane is insoluble in NMP and DMSO at room temperature and exhibits resistance.

[0007] Patent No. 5578300

[0008] However, due to the low molecular polarity of PPO membranes, while they are resistant to aprotic polar solvents such as NMP and DMSO, they have the problem of dissolving in nonpolar solvents such as toluene and benzene, which have similar Hansen solubility parameters.Furthermore, they dissolve in NMP at relatively high temperatures, which means that their solvent resistance is insufficient for use as organic solvent filtration membranes.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a separation membrane having excellent organic solvent resistance, acid resistance, and base resistance.

[0010] In view of the above problems, the present inventors have conducted extensive research and discovered the following: (1) that alkanolamines can be densely incorporated into the PPO side chains by a simple process of using a PPO membrane (BrPPO membrane) halogenated at the benzyl position as a precursor and immersing the membrane in an alkanolamine solution, (2) that this membrane has excellent resistance to not only water but also almost all organic solvents, (3) that the high hydrophilicity of the alkanolamine side chains results in excellent water wettability even after the membrane is dried, and (4) that a solvent-resistant membrane can be easily obtained with less membrane shrinkage, permeability degradation, and embrittlement (decreased elongation) due to crosslinking, compared to the solvent resistance of polymer membranes achieved by covalent crosslinking, which is commonly used in this field, and thus the present invention has been completed. That is, the present invention has the following configuration.

[0011] [1] A modified polyphenylene oxide separation membrane, in which at least a portion of the 2- and 6-benzyl positions are halogenated, i.e., a polyphenylene oxide precursor membrane in which at least a portion of the 2- and 6-benzyl positions are substituted with a halogeno group, characterized in that at least a portion of the halogeno groups are substituted with an alkanolamine. In other words, the modified polyphenylene oxide separation membrane of the present invention is characterized in that at least a portion of the 2- and 6-benzyl positions are substituted with an alkanolamine. [2] The modified polyphenylene oxide separation membrane according to [1], characterized in that the halogeno groups are bromine. [3] The modified polyphenylene oxide separation membrane according to [1] or [2], characterized in that the alkanolamine is monoethanolamine represented by chemical formula (3). (where R 1(wherein represents either hydrogen or a methyl group) [4] The modified polyphenylene oxide separation membrane according to any one of [1] to [3], wherein at least a portion of the halogeno groups are substituted with an alkanolamine and a polyfunctional amine. [5] The modified polyphenylene oxide separation membrane according to [4], wherein the polyfunctional amine is one or more selected from the group consisting of an alicyclic diamine, an aliphatic triamine, and an aromatic diamine. [6] A method for producing a modified polyphenylene oxide separation membrane, comprising immersing a precursor membrane made of a halogenated polyphenylene oxide in which at least a portion of the benzyl positions (2- and 6-positions) are halogenated in a reaction solution in which an alkanolamine is dissolved in an organic solvent in which the precursor membrane is insoluble, thereby substituting at least a portion of the halogeno groups at the benzyl positions with the alkanolamine. [7] A method for producing a modified polyphenylene oxide separation membrane according to [6], characterized in that a precursor membrane made of halogenated polyphenylene oxide in which at least a portion of the benzyl groups at the 2- and 6-positions have been halogenated is immersed in a reaction solution in which an alkanolamine and a polyfunctional amine are dissolved in an organic solvent in which the precursor membrane is insoluble, thereby substituting at least a portion of the halogeno groups at the benzyl positions with the alkanolamine and the polyfunctional amine. [8] A method for producing a modified polyphenylene oxide separation membrane according to [6] or [7], characterized in that the organic solvent is methanol or acetonitrile.

[0012] In the present invention, the modified PPO membrane having an alkanolamine introduced at the benzyl position has excellent solvent and chemical resistance, particularly alkali and acid resistance, and is capable of stable separation operations in a wide range of solvents, including protic polar solvents such as methanol, ethanol, and 2-propanol, aprotic polar solvents such as NMP, DMSO, and dimethylformamide (DMF), and nonpolar solvents such as toluene and hexane, under both acidic and basic conditions. Furthermore, due to the high hydrophilicity of the hydroxyl groups in the alkanolamine side chains, the membrane of the present invention has excellent water wettability, and the modified PPO membrane alone can be suitably used as an organic solvent separation membrane (e.g., ultrafiltration membrane, nanofiltration membrane, etc.).

[0013] 1 shows the permeability of various solvents through the separation membrane according to the present invention.

[0014] The separation membrane of the present invention is produced using polyphenylene oxide (PPO, poly-2,6-dimethyl-1,4-phenylene oxide) as a raw material. The chemical structure of PPO is represented by the following chemical formula (1). (In the formula, n represents an integer of 1 or more, preferably an integer of 2 or more, and more preferably an integer of 40 or more and 5000 or less.)

[0015] In the present invention, the weight average molecular weight of PPO is preferably 5,000 or more and 500,000 or less from the viewpoint of imparting sufficient viscosity to the membrane-forming solution to improve coating properties and spinnability and ensuring membrane strength.

[0016] In the present invention, in order to modify PPO with an alkanolamine or the like as described below, it is preferable to halogenate the hydrogen atoms of the methyl groups at the 2- and 6-positions of PPO (benzyl positions) by a known method. The halogen may be fluorine, chlorine, bromine, and / or iodine, but bromine is preferred because it has a high elimination ability, is inexpensive, and is easy to handle.

[0017] In the present invention, in the process of halogenating the benzyl position of PPO, a part of the benzene nucleus at the 3- and 5-positions may be substituted with a halogeno group. However, the halogeno group of the benzene nucleus may be S. N Since type 2 nucleophilic substitution reactions do not occur, it is preferable to use known reaction conditions that selectively halogenate the benzylic position. Specifically, carbon tetrachloride or chlorobenzene is preferably used as the reaction solvent. The reason for this is that by using these solvents with low halogen solubility, the halogen concentration in the reaction system can be kept low, resulting in preferential halogenation of the benzylic position. For example, it is known that when a polar solvent such as acetonitrile is used, only the benzene nucleus is halogenated. From the standpoint of ease of handling, it is preferable to avoid carbon tetrachloride, and chlorobenzene is preferred.

[0018] In the present invention, known halogenating agents such as simple halogens and N-halogenated succinimides can be used as the halogen source. The halogenation reaction is preferably carried out under an inert atmosphere such as argon or nitrogen at a reaction temperature of 110°C or higher for 3 hours or longer. The higher the reaction temperature, the higher the selectivity of halogenation to the benzyl position. However, since a side reaction of crosslinking of the polymer may occur at temperatures above 140°C, the reaction is more preferably carried out at a temperature of 115°C or higher but lower than 135°C.

[0019] In the present invention, methanol, ethanol, acetone, or the like is added to the reaction solution to precipitate the polymer, which is then washed with the same solvent and dried to obtain halogenated PPO (e.g., BrPPO), which is the PPO precursor that constitutes the PPO precursor film. Methanol is more preferably used as the solvent.

[0020] In the present invention, the degree of halogenation at the benzyl position of halogenated PPO can be determined by nuclear magnetic resonance (NMR) using, for example, deuterated chloroform as a solvent. The generalized chemical structure of halogenated PPO is shown in chemical formula (2). Depending on the degree of halogenation of the benzene nucleus and the benzyl position, various unit structures n i (i = 1 to k) can be generated, and the abundance ratio of each unit structure can be determined based on each characteristic peak in NMR. The detailed unit structures can also be identified using, for example, heteronuclear single quantum coherence spectroscopy (HSQC).

[0021]

[0022] Here, R 2 ~R 9 are each a halogeno group or hydrogen, and R 2 and R 3 represents a halogeno group on the benzene nucleus, and R 4 ~R 9 At least one of the n represents a halogeno group at the benzyl position. i is the mole fraction (n i represents 0 or greater and 1 or less).

[0023] In the present invention, the degree of halogenation (DBr) is defined as the average value per unit structure of the number of halogeno groups substituted at the benzyl position, and is represented by the following mathematical formula (1). PPO has two methyl groups at the 2- and 6-positions in the unit structure, and the number of hydrogen atoms at the benzyl position where substitution can occur is six, so DBr can take a value of 0 to 6.0. However, as far as the inventors are aware, 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 where 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.

[0024]

[0025] Here, N i_BzBr represents the number of halogeno groups substituted at the benzyl positions in the unit structure i.

[0026] On the other hand, the average number of halogeno groups substituted for hydrogen atoms in the benzene ring per structural unit is expressed by the following formula (2).

[0027]

[0028] Here, N i_ArBr represents the number of halogeno groups substituted on the benzene nucleus in the unit structure i.

[0029] In the present invention, the degree of halogenation DBr at the benzyl position shown above is preferably 0.5 or more and 2.0 or less. If this value is too low, the side chain modification by the alkanolamine and polyfunctional amine described below will be insufficient, and sufficient solvent resistance and water wettability (hydrophilicity) of the film may not be exhibited. On the other hand, if it is too high, the amount of halogen used will increase too much, which will reduce economic rationality, and side reactions such as crosslinking may also occur easily during the reaction process.

[0030] In the present invention, there is no particular limitation on the degree of halogenation DBr of the benzene nucleus, but it is preferably 0 or more and 1.0 or less. If this value is too high, the degree of halogenation DBr at the benzyl position will be relatively low, which may cause problems such as an excessive increase in the amount of halogen used or insufficient solvent resistance. Depending on the reaction conditions, there may be a unit structure in which both halogenation of the benzene nucleus and halogenation of the benzyl position have occurred.

[0031] Next, a membrane is formed using the obtained halogenated PPO polymer. The membrane form can be selected from flat membranes, hollow fiber membranes, and the like. Because halogenated PPO can be dissolved in NMP, DMF, and the like, solution membrane formation is preferred. In this case, a certain amount of non-solvent can be added to a good solvent such as NMP to control phase separation. For example, polyethylene glycol, glycerin, polypropylene glycol, nonionic surfactants, ionic surfactants, and the like may be appropriately selected and added.

[0032] It is practically impossible to replace the halogeno groups of halogenated PPO with alkanolamines before film formation. The PPO of the present invention, whose side chains have been modified with alkanolamines, is insoluble in any organic solvent known to the inventors, making film formation itself difficult. Therefore, it is preferable to carry out a modification treatment with an alkanolamine or a polyfunctional amine after the halogenated PPO film has been produced.

[0033] To produce a halogenated PPO flat membrane, a halogenated PPO membrane-forming solution is applied to a nonwoven fabric made of a solvent-resistant material such as polyethylene terephthalate, polyethylene, polypropylene, or polyphenylene sulfide using a doctor blade or the like, and the fabric is then immersed in a coagulation bath of a nonsolvent (typically water). Polyphenylene sulfide (PPS) is preferred as the nonwoven fabric. PPS has excellent solvent resistance and is also highly resistant to alkalis and acids. To produce a hollow fiber membrane, the halogenated PPO membrane-forming solution is extruded from a double cylindrical nozzle together with the inner liquid, and the fabric is then immersed in a coagulation bath.

[0034] In the above-mentioned membrane-forming process, the polymer concentration of the membrane-forming solution, the discharge temperature, the temperature and composition of the coagulation bath, the transport speed, and other process parameters may be appropriately set based on known knowledge.

[0035] The obtained film is preferably dried to an absolute dry state by natural air drying, vacuum drying, etc. If a large amount of moisture remains in the film, the nucleophilic substitution reaction with the amine-based nucleophilic agent described below may not proceed sufficiently.

[0036] A dried halogenated PPO membrane (flat membrane or hollow fiber membrane) is immersed in a solution containing an amine-based nucleophile, i.e., an alkanolamine or a polyfunctional amine, to undergo a nucleophilic substitution reaction. The halogeno group substituted at the benzyl position of the halogenated PPO is easily substituted by the nucleophile. Examples of nucleophiles include amines, cyanide ions, azide ions, hydroxide ions, phenolates, and sulfinates. The use of a polyfunctional nucleophile can introduce covalent crosslinks between PPO molecular chains. Amines are preferred as nucleophiles because they allow for easy reaction. Primary, secondary, or tertiary amines can be used as amines. Alkanolamines are preferred. Specifically, the use of monoethanolamine, represented by chemical formula (3), or N-methylaminoethanol can impart high solvent resistance to the PPO membrane. Although the details of the mechanism by which alkanolamine substitution improves solvent resistance are not entirely clear, the side chains substituted with these alkanolamines have an extremely hydrophilic structure that easily forms intermolecular hydrogen bonds via hydroxyl groups, while the PPO main chain is a hydrophobic, high-strength aromatic polymer. It is believed that the insolubility in organic solvents with a wide range of solubility parameters is achieved by having these hydrophilic and hydrophobic properties within the molecular structure. Furthermore, by having a high density of hydroxyl groups in the side chains, the resulting modified PPO film has good wettability, allowing repeated drying and wetting without the need for wetting treatment with alcohol or the like, making it suitable for use in composite film formation processes such as interfacial polymerization.

[0037] Here, R 1 represents either a hydrogen or a methyl group.

[0038] The modified polyphenylene oxide constituting the modified polyphenylene oxide separation membrane according to the present invention has the following unit structure.

[0039] (In the formula, R 2 and R 3 are each a halogeno group or hydrogen, and R 4 ~R 9 are a halogeno group, hydrogen, and an alkanolamino group [—N(R 1 ) R 10 OH (in the formula, R 1 has the same meaning as above, and R 10 is C 2-6 alkanediyl group)] or a polyfunctional amino group, R 4 ~R 9 At least one of the groups represents an alkanolamino group.

[0040] "C 2-6 The term "alkanediyl group" refers to a linear or branched divalent saturated aliphatic hydrocarbon group having 2 to 6 carbon atoms. Examples include ethylene, n-propylene, methylethylene, n-butylene, methylpropylene, dimethylethylene, n-pentylene, and n-hexylene. Preferably, C 2-4 It is an alkanediyl group, more preferably ethylene.

[0041] In the modified polyphenylene oxide constituting the modified polyphenylene oxide separation membrane according to the present invention, the average number of alkanolamines substituted at the benzyl position per unit structure is preferably 0.5 to 2.0. If this value is 0.5 or more, the solvent resistance of the polyphenylene oxide can be sufficiently improved. On the other hand, since it may be difficult to introduce three or more alkanolamines into a unit structure, this value is preferably 2.0 or less.

[0042] It is also preferable to partially incorporate a polyfunctional amine component, such as a diamine or triamine, which is a covalent crosslinking component, in addition to the alkanolamine, to enhance mechanical strength while maintaining the hydrophilicity provided by the alkanolamine. In this case, the structure of the diamine and triamine is not particularly limited, but alicyclic diamines such as piperazine, aliphatic triamines such as diethylenetriamine, and aromatic diamines such as phenylenediamine can be used, and primary, secondary, and tertiary amines can be used as the amine. On the other hand, when solvent resistance is imparted to a PPO membrane using only a covalent crosslinking component, the crosslinking can cause significant volume shrinkage and pore size shrinkage of the membrane, resulting in a significant decrease in solvent permeability. Furthermore, if there are too many covalent crosslinks, the membrane can become embrittled and crack, or, in the case of a hollow fiber membrane, problems such as low elongation and significantly reduced handleability can occur. The term "polyfunctional amino group" refers to a group in which one hydrogen atom has been removed from the amino group of a polyfunctional amine.

[0043] The concentrations of the alkanolamine and the polyfunctional amine of the covalent cross-linking component in the nucleophilic substitution reaction may be adjusted as appropriate, but are preferably 1% by mass or more and 10% by mass or less. The solvent must be an organic solvent other than water, and must not dissolve the halogenated PPO film. Water is used in the presence of S N It seems that type 2 nucleophilic substitution reaction hardly proceeds. Methanol, acetonitrile, dimethyl sulfoxide, etc. can be preferably used. Methanol and acetonitrile are more preferred. The reaction time is preferably adjusted appropriately within the range of 1 hour to 24 hours. Renewing the solution while reacting is also a preferred treatment to increase the degree of substitution.

[0044] The modified PPO (m-PPO) after the nucleophilic substitution reaction may be directly subjected to separation, or may be rinsed with methanol or pure water, or may be dried and stored. Because the membrane of the present invention is highly hydrophilic, it can be stored in a dry state and, if necessary, wetted with a desired solvent before use in a separation operation, or used as a support membrane for a composite membrane prepared by interfacial polymerization, etc.

[0045] This application claims the benefit of priority based on Japanese Patent Application No. 2023-132912, filed on August 17, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-132912, filed on August 17, 2023, are incorporated herein by reference.

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0047] Example 1: Production of Modified Polyphenylene Oxide Separation Membrane (1) Synthesis of Halogenated (Brominated) Polyphenylene Oxide 40 g of polyphenylene oxide ("181803" 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 uniform, transparent solution was obtained, a predetermined amount of N-bromosuccinimide and a radical initiator were added. With vigorous stirring, the reaction solution was heated to and maintained at 120°C while monitoring the heating rate in an oil bath. The reaction was allowed to proceed for 6.5 hours. After allowing the reaction solution to cool, the precipitated flake-like polymer was crushed in 2 L of methanol using a blender. The polymer was then thoroughly washed, with the methanol being renewed. The polymer was then vacuum-dried at 60°C to obtain a powdered brominated polyphenylene oxide (BrPPO) polymer.

[0048] (2) Chemical structure evaluation of brominated polyphenylene oxide The chemical structure analysis of BrPPO polymer was performed using a nuclear magnetic resonance spectrometer ( 1 H-NMR, 13 The measurement was carried out using a C-NMR under the following conditions: Apparatus: Fourier transform nuclear magnetic resonance apparatus ("AVANCE500" manufactured by Bruker Biospin) Sample: 5 to 50 mg of sample was dissolved in 1.0 mL of deuterated chloroform.

[0049] (3) Preparation of Brominated Polyphenylene Oxide (BrPPO) Flat Membrane NMP and polyethylene glycol (PEG400) with a molecular weight of 400 were added to a predetermined amount of BrPPO polymer and kneaded and dissolved at 60°C for 6 hours to prepare membrane-forming stock solutions of various concentrations. After degassing under reduced pressure, this membrane-forming stock solution was applied to a 300 mm wide, 120 μm thick polyphenylene sulfide (PPS) nonwoven fabric using a doctor blade and coagulated in a water bath at a predetermined temperature for 10 minutes. The coagulated membrane was thoroughly washed with water and air-dried to obtain a BrPPO flat membrane (PPO precursor membrane). The membrane was cut into a circle with a diameter of 48 mm and subjected to evaluation.

[0050] (4) Preparation of Brominated Polyphenylene Oxide (BrPPO) Hollow Fiber Membrane A predetermined amount of BrPPO polymer was mixed with NMP and dissolved at 60°C for 6 hours to prepare a membrane-forming solution. This membrane-forming solution was degassed under reduced pressure and then extruded through a double cylindrical nozzle together with the spinning solution and inner solution (50% NMP aqueous solution). The solution was coagulated in a water bath at 40°C and thoroughly washed with water. A predetermined number of fibers were wound onto a take-up roller to produce a fiber bundle. The cross-sectional shape of the BrPPO hollow fiber membrane was adjusted to an outer diameter of 250 μm and an inner diameter of 150 μm. The bundle contained 100 fibers. The ends of the naturally dried bundle were loosened and inserted into a plastic sleeve and embedded in a two-component epoxy resin. After the epoxy resin cured, the adhesive end was cut with a knife to expose the hollow portion of the membrane, creating a permeate port.

[0051] (5) Side Chain Modification Treatment of BrPPO Membrane: BrPPO flat membranes and hollow fiber membranes in an absolute dry state were immersed in a 3 to 6 mass % methanol or acetonitrile solution of a specific amine-based nucleophile at room temperature for a specific time, and debromination and introduction of amine were carried out by a nucleophilic substitution reaction to obtain a modified polyphenylene oxide (m-PPO) membrane. After rinsing with methanol, the membrane was air-dried and stored until use.

[0052] (6) Evaluation of the Degree of Modification of m-PPO Films The degree of modification of BrPPO films was evaluated using X-ray photoelectron spectroscopy (XPS) for BrPPO films and m-PPO films before and after immersion in an amine solution. In elemental composition analysis using XPS, it is difficult to eliminate the influence of residual solvents, additives, and impurities contained in the polymer during film formation. However, it was confirmed that the bromine content in all m-PPO film samples had decreased by 80% or more compared to before the reaction, and the content of nitrogen derived from amines had increased, indicating that most of the benzylic bromine had been substituted with amines. The equipment and measurement conditions used for XPS analysis are as follows: Apparatus: K-Alpha+ (manufactured by Thermo Fisher Scientific) [Measurement conditions] Excitation X-ray: Monochromated 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

[0053] Comparative Example 1: Production of Unmodified PPO Membrane Polyphenylene oxide (PPO, "181803" manufactured by Sigma-Aldrich) was used and dissolved in a mixed solvent of NMP and PEG400 at 130°C with stirring to a polymer concentration of 25% by mass to prepare a membrane-forming solution. This membrane-forming solution was extruded through a double cylindrical nozzle with a 50% by mass aqueous NMP solution as the inner solution at a nozzle temperature of 90°C and coagulated in a water bath set at 40°C. The membrane was then washed with water and dried to prepare a hollow fiber membrane. The cross-sectional shape of the hollow fiber membrane was adjusted to an outer diameter of 250 μm and an inner diameter of 150 μm.

[0054] Test Example 1: Organic Solvent Resistance Test A 1 cm square flat membrane or a 1 cm long hollow fiber membrane was immersed in various organic solvents for 24 hours at room temperature or heated to 100°C on a hot plate, and the solvent resistance of the membrane was evaluated according to the following criteria. However, for solvents with a boiling point of less than 100°C, the temperature was set 10°C lower than the boiling point for evaluation. The test was conducted on the m-PPO membrane of Example 1, the unmodified PPO membrane of Comparative Example 1, and a commercially available polyethersulfone membrane (ASFIL025010MFPES, AS ONE Corporation). The results are shown in Table 1. ○: Completely insoluble ×: Swelled significantly at room temperature and dissolved at high temperatures XX: Dissolved at room temperature

[0055]

[0056] As shown in Table 1, commercially available polyethersulfone membranes dissolved in some organic solvents even at room temperature. The unmodified PPO membrane (Comparative Example 1) also dissolved in chlorobenzene, toluene, and chloroform even at room temperature. Furthermore, it swelled significantly in tetrahydrofuran, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide at room temperature and dissolved at high temperatures, indicating insufficient organic solvent resistance. In contrast, the modified PPO membrane of the present invention exhibited resistance to all organic solvents tested.

[0057] Example 2 (1) Preparation of Brominated Polyphenylene Oxide (BrPPO) Flat Membrane BrPPO was synthesized according to the method described in Example 1 (1) above. The amount of N-bromosuccinimide added was 107 g, and 2.0 g of azobisisobutyronitrile was used as the radical initiator. NMR analysis of the obtained BrPPO revealed that the degree of halogenation (bromination) at the benzyl position, DBr, was 1.46. The degree of halogenation (bromination) at the benzene nucleus, DBr2, was 0.22. Next, a BrPPO flat membrane was prepared using the obtained BrPPO according to Example 1 (3) above. The BrPPO polymer concentration in the membrane-forming solution was 25% by mass, and the temperature of the water bath was set to 40°C. The pure water permeability of the BrPPO membrane measured at 5 bar was 425 L / (m 2 The measured value was 1.5 h bar. The bone-dried membrane sample was then immersed in a 3% by mass solution of monoethanolamine (MEA) in methanol, and side-chain modification treatment was carried out for 24 hours. After the reaction was completed, the membrane was rinsed with methanol and allowed to air-dry. The results of XPS analysis of the membrane before and after side-chain modification treatment are shown in Table 2. The calculated and experimental values ​​for the elemental composition of the BrPPO membrane (precursor membrane) and m-PPO membrane (modified PPO membrane) were generally consistent, and it was revealed that most of the benzyl-positioned halogens (bromine) had been substituted with monoethanolamine.

[0058]

[0059] Example 3: A BrPPO hollow fiber membrane was produced according to the method described in section (4) of Example 1. Using the same BrPPO polymer as in Example 2, a membrane-forming solution with a polymer concentration of 25% by mass was prepared. This was extruded using a double cylindrical nozzle together with an inner solution consisting of a 50% by mass NMP aqueous solution, and then immersed in a water bath set at 40°C to coagulate. The hollow fiber membrane was then produced by washing with water and drying. The cross-sectional shape of the hollow fiber membrane was adjusted to an outer diameter of 250 μm and an inner diameter of 150 μm. The bone-dried membrane sample was immersed in a 3% by mass solution of monoethanolamine (MEA) in methanol and subjected to side chain modification treatment for 24 hours. After completion of the reaction, the membrane was rinsed with methanol and vacuum dried.

[0060] Example 4 A flat membrane was produced in the same manner as in Example 2, except that the BrPPO polymer concentration was set to 32% by mass and the water bath temperature was set to 20° C. In addition, a side chain modification treatment was carried out under the same conditions as in Example 2. In Example 4, aiming at a nanofiltration membrane, a high-concentration BrPPO polymer stock solution was used to produce an asymmetric nanofiltration membrane in which a dense skin layer was formed on the membrane surface.

[0061] Example 5 BrPPO was synthesized in the same manner as in Example 2, except that 170 g of N-bromosuccinimide and 2.0 g of azobisisobutyronitrile radical initiator were used. NMR analysis revealed that the degree of halogenation (bromination) at the benzyl position, DBr, was 1.94. The degree of halogenation (bromination) at the benzene nucleus, DBr2, was 0.36. A flat membrane was produced in the same manner as in Example 2.

[0062] Example 6 BrPPO was synthesized in the same manner as in Example 2, except that 60 g of N-bromosuccinimide and 2.0 g of azobisisobutyronitrile radical initiator were used. NMR analysis revealed that the degree of halogenation (bromination) at the benzyl position, DBr, was 0.74. Furthermore, the degree of halogenation (bromination) of the benzene nucleus, DBr2, was 0.11. Membrane formation was carried out in the same manner as in Example 2, except that the reaction solvent for MEA was changed from methanol to acetonitrile.

[0063] Example 7 A flat membrane was prepared in the same manner as in Example 4, except that N-methylaminoethanol (NMAE) was used as the alkanolamine. In Example 7, aiming at a nanofiltration membrane, a high-concentration BrPPO polymer stock solution was used to prepare an asymmetric nanofiltration membrane in which a dense skin layer was formed on the membrane surface.

[0064] Example 8 A membrane was formed in the same manner as in Example 2, except that a 3 mass% methanol solution in which MEA as the alkanolamine and piperazine (PIP) as the diamine were mixed in a weight ratio of 95:5 was used as the reaction solution.

[0065] Example 9 A membrane was formed in the same manner as in Example 2, except that a 3 mass% methanol solution in which MEA as the alkanolamine and piperazine (PIP) as the diamine were mixed in a mass ratio of 80:20 was used as the reaction solution.

[0066] Example 10 A membrane was formed in the same manner as in Example 1, except that a 3 mass% methanol solution containing MEA as the alkanolamine and diethylenetriamine (DETA) as the diamine in a mass ratio of 95:5 was used as the reaction solution.

[0067] Comparative Example 2: Production of Unmodified BrPPO Flat Membrane BrPPO was synthesized in the same manner as in Example 2, except that 35 g of N-bromosuccinimide and 2.0 g of azobisisobutyronitrile radical initiator were used, and an unmodified BrPPO flat membrane was produced. NMR analysis revealed that the degree of halogenation (bromination) at the benzyl position, DBr, was 0.42. Furthermore, the degree of halogenation (bromination) at the benzene nucleus, DBr2, was 0.05. A membrane was produced in the same manner as in Example 2.

[0068] Comparative Example 3: Production of PIP-modified PPO membrane A PIP-modified PPO membrane was produced in the same manner as in Example 2, except that covalent crosslinking was introduced using only PIP as the amine.

[0069] The membrane structures of Examples 2 to 10 and Comparative Examples 1 to 3 are summarized below.

[0070]

[0071] Test Example 2: Separation test in an aqueous system The PPO flat membranes or hollow fiber membranes of Examples 2 to 10 and Comparative Examples 1 to 3 were sufficiently wetted with water and subjected to performance evaluation using an evaluation device consisting of a stainless steel pressure vessel, a supply water tank, and a pump.

[0072] (1) Measurement of NaCl Rejection The rejection of sodium chloride (NaCl) was measured for the modified PPO membranes of Examples 4 and 7, which are intended for use as nanofiltration membranes. The NaCl rejection of other membranes, which are intended for use as substrates for ultrafiltration membranes, was not measured. A feed aqueous solution prepared to a concentration of 1500 mg / L was run for 1 hour at 25°C and a pressure of 15 bar, after which the permeated water was collected from the membrane and the weight of the permeated water was measured using an electronic balance. The permeated water weight was converted to the permeated water volume at 25°C using the following formula: Permeated water volume (L) = Permeated water weight (kg) / 0.99704 (kg / L) The amount of permeated water per unit time, unit membrane area, and unit pressure is represented by A as permeance. The water permeability A was evaluated using pure water at a pressure of 5 bar or 15 bar and calculated using the following formula: A [L / (m 2 ・h ・bar)] = permeate volume [L] / membrane area [m 2 ] / sampling time [h] / measurement pressure [bar]

[0073] The NaCl rejection rate was evaluated as follows. The conductivity of the membrane permeate water collected in the above water permeation rate measurement and the feed water was measured using an electric conductivity meter (CM-25R, manufactured by DKK-TOA Corporation). The rejection rate was calculated using the following formula. The results are shown in Table 4. NaCl rejection rate [%] = (1 - membrane permeate water conductivity [μS / cm] / feed aqueous solution conductivity [μS / m]) × 100

[0074] (2) Measurement of PEG Rejection Rate The evaluation of neutral molecule rejection rate in aqueous systems was performed using polyethylene glycol (PEG). For the modified PPO membranes of Examples 4 and 7 intended for nanofiltration membranes, PEG with a molecular weight of 400 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used, and the PEG solution pressure was adjusted to 15 bar. For other membranes intended for use as ultrafiltration membrane substrates, PEG with a molecular weight of 300,000 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used, and the PEG solution pressure was adjusted to 5 bar. An aqueous solution with a PEG concentration of 200 mg / L was used, and the operation was performed at 25°C for 1 hour. After that, the permeate from the membrane was sampled, and the feed solution concentration and the permeate concentration were measured using a total organic carbon analyzer ("ON-LINE TOC-VCSH" Shimadzu Corporation). The PEG rejection rate was calculated using the following formula. The results are shown in Table 4. PEG rejection rate [%] = 100 x [1-(permeate PEG concentration) / (feed solution PEG concentration)]

[0075] Test Example 3: Membrane wettability test Pure water was dropped onto the surface of an absolutely dried flat membrane and a hollow fiber membrane to check whether spontaneous wetting of the membrane surface and capillary penetration of water into the membrane occurred. If wetting and penetration of the membrane occurred, it was judged as wettable (◯), and if droplets with a contact angle were generated on the membrane surface, it was judged as not wettable (×).

[0076] Test Example 4: Membrane permeability test in organic solvent systems A flat membrane or hollow fiber membrane thoroughly washed with NMP was loaded into a stainless steel pressure vessel sealed with a sealant made by FFKM, and an organic solvent was transferred from a 500 mL HPLC screw-cap bottle to the pressure vessel using an HPLC preparative pump for evaluation. The solvent permeability A was measured at 0.5 bar and calculated using the following formula. In Examples 4 and 7, a high-concentration BrPPO polymer stock solution of 32 mass% was used to prepare an asymmetric nanofiltration membrane in which a dense skin layer was formed on the membrane surface. Therefore, since the amount of filtrate in the membranes of Examples 4 and 7 was smaller than that of the other membranes, the pressure was adjusted to 15 bar. The results are shown in Table 4. A [L / (m 2 ・h ・bar)] = permeate volume [L] / membrane area [m 2 ] / sampling time [h] / measurement pressure [bar]

[0077] Test Example 5: Pressure resistance test of membrane in organic solvent The pressure resistance was evaluated by measuring the permeability of the m-PPO membrane when filtering NMP solvent at a pressure of 2 bar (A2.0) and the permeability of the membrane when filtering at a pressure of 1 bar (A2.0). 1.0 Ratio A 2.0 / A 1.0 The results are shown in Table 4. The modified PPO membranes of Examples 4 and 7, which are intended as nanofiltration membranes, were not evaluated.

[0078] Test Example 6: Membrane fractionation performance test in organic solvent system The fractionation performance in organic solvent of the modified PPO membranes of Examples 4 and 7, which are intended for nanofiltration membranes, was evaluated. The fractionation performance of other membranes intended for use as ultrafiltration membrane substrates was not evaluated. As a marker for membrane separation tests in NMP, diol-type polypropylene glycol (PPG400) with a molecular weight of 400 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used. The PPG400 separation test was performed after stabilization operation at 25 ° C and a pressure of 15 bar for 6 hours, and then the permeate was collected. Peak analysis of PPG400 in the feed solution and the permeate was performed using high-performance liquid chromatography (HPLC), and the rejection rate of PPG400 was determined from the area ratio of the peak top molecular weight components before and after permeation. The results are shown in Table 4. Rejection rate [%] = 100 × [1 - (peak area of ​​peak top molecular weight component in permeate) / (peak area of ​​peak top molecular weight component in feed solution)] The HPLC measurement conditions are as follows. [HPLC conditions] Apparatus: Thermo Fisher Scientific Vanquish Column: Waters BEH C18 2.1 × 150 mm Mobile phase: A ultrapure water, B acetonitrile 0 min (5% B) 15 (60) 20 (100) 25 (100) Flow rate: 0.25 mL / min Column temperature: 40°C Injection volume: 5 μL Detection: Charged aerosol detector (CAD) Drying tube temperature: 35°C

[0079] Test Example 7: Alkali and acid resistance test of m-PPO membrane (modified PPO membrane) An m-PPO flat membrane sample was immersed in 100 mL of 1 mol / L sodium hydroxide (NaOH) and hydrogen chloride (HCl), respectively, for one week, with the solution being changed every day. Thereafter, a PEG fractionation test was carried out in an aqueous system to compare the resistances.

[0080]

[0081] When the unmodified PPO dried membrane of Comparative Example 1 was immersed in NMP at room temperature, it swelled significantly, making it impossible to evaluate its performance in an organic solvent. Although the membrane of Comparative Example 1 is an unmodified PPO membrane, its wettability with water was evaluated and found to be completely insufficient. The unmodified BrPPO membrane of Comparative Example 2 also swelled significantly when immersed in NMP, making it difficult to evaluate its performance in an organic solvent. The wettability of the unmodified BrPPO membrane of Comparative Example 2 with water was also completely insufficient. When the wettability of the membrane of Comparative Example 3, in which no MEA was introduced and only piperazine (PIP) was introduced, was checked, spontaneous wetting did not occur, and the wettability was poor (×). Since a wetting treatment with ethanol or the like was required to allow water permeation, handling was impaired.

[0082] The wettability evaluation of the dry m-PPO membrane (modified PPO membrane) of Example 2 confirmed spontaneous wetting, and the wettability was good (good). After immersing the dry membrane in pure water for 30 minutes, the pure water permeability measured at 5 bar was 390 L / (m 2 ·h·bar), and it was confirmed that the permeability was not significantly impaired before and after the side chain modification treatment and natural drying. In the aqueous separation evaluation, the rejection rate of PEG300k was 93%, and it was a porous membrane at the level of an ultrafiltration (UF) membrane. Next, this membrane was immersed in NMP for 2 hours to perform solvent replacement, and then the NMP permeability was measured using a flat membrane evaluation cell, and it was found to be 145 L / (m 2 The ratio A of the permeabilities at pressures of 0.5 bar and 2.0 bar was 2.0 / A 0.5The value was 0.96, and the pressure resistance in NMP was good. Furthermore, the results of a permeation test of solvents other than NMP on the membrane of Example 2 are shown in Figure 1. The solvent permeability was measured while sequentially replacing the solvents with solvents having significantly different solubility parameters (water, NMP, ethanol, toluene, methanol, toluene), and the results showed good permeability for all solvents. Furthermore, even when the solvent was replaced with water again, almost no change was observed from the initial permeability, suggesting that no irreversible changes in the membrane structure due to solvent replacement occurred.

[0083] It was revealed that the hollow fiber membrane of Example 3 also exhibits excellent wettability and organic solvent resistance, and can therefore be used for separation in the presence of organic solvents.

[0084] In the aqueous evaluation, the m-PPO membrane of Example 4 had a NaCl rejection rate of 68% and a PEG400 rejection rate of 98%, demonstrating that the m-PPO membrane of Example 4 has fractionation characteristics at the same level as nanofiltration (NF) membranes. The NMP permeability was 0.4 L / (m 2 The experimental pressure (MPa) was 1.5 MPa (1.5 MPa) and the rejection rate of PPG400 in NMP was 95%, demonstrating that the m-PPO membrane exhibits excellent NF membrane performance even in NMP. Furthermore, a sample of the m-PPO membrane at the NF membrane level of Example 4 was separately prepared, and a 1 M aqueous NaOH solution and an aqueous HCl solution were prepared. After a one-week immersion test, a PEG400 separation test was conducted in an aqueous system. The PEG400 rejection rate was 97-98% in both cases before and after the immersion test, with almost no change in separation performance. This demonstrates that the m-PPO membrane has excellent chemical resistance, i.e., excellent alkali resistance and acid resistance.

[0085] In Example 5, as in Example 2, an m-PPO membrane of UF membrane quality was obtained, and the pressure resistance in NMP was also good.

[0086] A comparison of Example 6 and Example 2 confirmed that the transmittance and pressure resistance in NMP were reduced, but that solvent resistance was good. This slight decrease in performance was thought to be due to a decrease in the intermolecular hydrogen bonds derived from the MEA caused by a decrease in the degree of amine substitution at the benzyl position of m-PPO.

[0087] The NMP permeability of the flat membrane of Example 7, which was produced using N-methylaminoethanol (NMAE) as the MEA, was 0.15 L / (m 2 .h.bar), and the rejection rate of PPG400 in NMP was 92%, confirming that the m-PPO membrane using NMAE also exhibits excellent NF membrane performance in NMP.

[0088] In Example 8, a 3 mass% methanol solution containing MEA as the alkanolamine and piperazine (PIP) as the diamine mixed in a weight ratio of 95:5 was used. As in Example 2, an m-PPO membrane of UF membrane quality was obtained. However, a notable feature was the low pressure resistance A 2.0 / A 0.5 was 1.0, and a tendency for improvement in pressure resistance was confirmed.

[0089] In Example 9, which used a 3% by mass methanol solution in which MEA was used as the alkanolamine and PIP was used as the diamine in a mass ratio of 80:20, and in Example 10, which used a 3% by mass methanol solution in which MEA was used as the alkanolamine and diethylenetriamine (DETA) was used as the diamine in a mass ratio of 95:5, the pressure resistance was particularly good, similar to Example 8.

[0090] INDUSTRIAL APPLICABILITY The present invention can provide a separation membrane having excellent organic solvent resistance, acid resistance, and base resistance, and therefore has industrial applicability.

Claims

1. A modified polyphenylene oxide separation membrane, comprising a polyphenylene oxide precursor membrane in which at least a portion of the 2- and 6-benzyl positions are halogenated, and at least a portion of the halogeno groups are substituted with alkanolamine.

2. The modified polyphenylene oxide separation membrane according to claim 1, wherein the halogeno group is bromine.

3. The modified polyphenylene oxide separation membrane according to claim 1, wherein the alkanolamine is monoethanolamine represented by the chemical formula (3). (Here, R 1 represents either hydrogen or a methyl group) 4. The modified polyphenylene oxide separation membrane according to claim 1, wherein at least a portion of said halogeno groups is substituted with an alkanolamine and a polyfunctional amine.

5. The modified polyphenylene oxide separation membrane according to claim 4, characterized in that the polyfunctional amine is at least one selected from the group consisting of alicyclic diamines, aliphatic triamines and aromatic diamines.

6. A method for producing a modified polyphenylene oxide separation membrane, comprising immersing a precursor membrane made of a halogenated polyphenylene oxide in which at least a portion of the 2- and 6-benzyl positions are halogenated in a reaction solution in which an alkanolamine is dissolved in an organic solvent in which the precursor membrane is insoluble, thereby replacing at least a portion of the halogeno groups at the benzyl positions with the alkanolamine.

7. A method for producing a modified polyphenylene oxide separation membrane as described in claim 6, characterized in that a precursor membrane consisting of a halogenated polyphenylene oxide in which at least a portion of the 2- and 6-benzyl positions are halogenated is immersed in a reaction solution in which the alkanolamine and a polyfunctional amine are dissolved in an organic solvent in which the precursor membrane is insoluble, and at least a portion of the halogeno groups at the benzyl positions are replaced with the alkanolamine and the polyfunctional amine.

8. The method for producing a modified polyphenylene oxide separation membrane according to claim 6 or 7, characterized in that the organic solvent is methanol or acetonitrile.

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