JP5896295B2 - Separation membrane for nanofiltration - Google Patents

Description

  The present invention relates to a separation membrane suitable for nanofiltration, in which a salt removability and water permeability are compatible at a high level while using a material excellent in chemical resistance.

  In order to stably operate the nanofiltration membrane for a long period of time, appropriate pretreatment such as sterilization of water to be treated and removal of turbid components and periodic membrane cleaning are indispensable as in the case of a reverse osmosis membrane. This is because when fouling components are deposited on the surface of the nanofiltration membrane or when slime is adhered due to the growth of microorganisms, the performance is significantly reduced. Examples of the pretreatment include removal of scale and fouling-causing substances by pH adjustment, membrane treatment, and the like, and membrane washing includes the use of an alkaline chemical solution, a chlorine chemical solution, particularly sodium hypochlorite.

  Regarding the relationship between the method of cleaning the membrane and the characteristics of the membrane material, membranes that have been widely commercialized so far are described as an example. Mainly cellulose triacetate (CTA, see Patent Document 1) and aromatic polyamide (PAm, Patent Document 2). CTA-based membranes have superior chlorine resistance compared to PAm-based membranes, and are particularly excellent in cleaning with sodium hypochlorite and membrane performance recoverability, but have the disadvantage of being weak in alkali resistance and limiting the use of alkaline chemicals. Have. Conversely, PAm-based films are superior in alkali resistance compared to CTA-based films, but have a drawback that the use of chlorine-based chemicals is limited because of their extremely low chlorine resistance.

  In order to compensate for these drawbacks, Patent Document 3 proposes a separation membrane using a polymer having a sulfonated polyarylethersulfone structure. The film thus obtained has improved chemical resistance, but has a problem of poor water permeability and unsuitable for practical use. In order to solve this problem, Patent Document 4 attempts to achieve both water permeation performance, salt removal performance, and chemical durability by thinly coating a sulfonated polyarylethersulfone on the PAm-based composite membrane. However, this method has a problem that since the coating layer is thin, there is anxiety in maintaining long-term chemical resistance, and the cost is increased due to the complexity of the film forming process.

  As described above, conventional separation membranes have problems in any of salt removal, water permeability, and chemical resistance, and there is currently no one that has realized these characteristics at a high level. .

Japanese Patent No. 3591618 Japanese Patent No. 2794785 Japanese Patent Publication No. 07-67529 JP-A-10-57883

  The present invention was devised in view of the current state of the prior art, and its purpose is to provide a salt removability required for nanofiltration while using a material having chemical resistance (alkali resistance, chlorine resistance). An object of the present invention is to provide a separation membrane having a high level of water permeability.

  As a result of intensive studies to achieve the above object, the present inventors have used a specific sulfonated polyarylene ether sulfone polymer having excellent chemical resistance as a material for the nanofiltration membrane, and the water content of the membrane is restricted. By controlling the position of the peak top of the origin to a specific chemical shift value region, it was found that the sulfonic acid group in the membrane and bound water interact well to achieve both high salt removal and water permeability. The present invention has been completed.

That is, the present invention has the following configurations (1) to (7).
(1) Proton which is a separation membrane made of a sulfonated polyarylene ether sulfone polymer containing a constituent represented by the following general formula [I] and which measures water molecules in the membrane using the water-containing separation membrane In the nuclear magnetic resonance spectrum, the relationship between the chemical shift A (ppm) of the spectral peak top derived from bound water and the chemical shift B (ppm) of the spectral peak top derived from bulk water is B−0.30 ≦ A <B−0. 14. A separation membrane for nanofiltration characterized by satisfying .14.
In the formula, X is H or a monovalent cation species, and n is an integer of 10 to 50.
(2) The separation membrane according to (1), wherein the logarithmic viscosity of the sulfonated polyarylene ether sulfone polymer is 1.0 to 2.3 dL / g.
(3) The separation membrane according to (1) or (2), wherein the sulfonated polyarylene ether sulfone polymer has a sulfonic acid group content of 0.5 to 2.3 meq / g.
(4) The separation membrane according to any one of (1) to (3), wherein no crystallization peak is observed in observation by differential scanning calorimetry.
(5) The separation membrane according to any one of (1) to (4), wherein the separation membrane is a hollow fiber membrane having an inner diameter of 70 to 100 μm and an outer diameter of 140 to 175 μm.
(6) The separation membrane according to (5), wherein pores having a diameter of 10 nm or more are not observed in a film thickness portion within 1 μm from the outer peripheral portion of the hollow fiber.
(7) The separation membrane according to (5) or (6), wherein the yield strength in a wet state is 5 MPa or more and less than 9 MPa.

  Since the separation membrane of the present invention uses a specific sulfonated polyarylene ether sulfone polymer as a material, it has high chemical resistance and strong resistance to both alkaline chemical solutions and chlorinated chemical solutions used for membrane cleaning. Have In addition, since the separation membrane of the present invention controls the position of the peak top derived from bound water when containing water within a specific chemical shift value range, the sulfonic acid groups in the membrane and water molecules interact efficiently. As a result, the salt removability and water permeability required for nanofiltration can be achieved at a high level.

An example of a proton NMR spectrum chart is shown.

  Conventionally, cellulose triacetate (CTA) and crosslinked aromatic polyamide (PAm) have been used as materials for reverse osmosis membranes and nanofiltration membranes. CTA is excellent in chlorine resistance, but has a problem inferior in alkali resistance. On the other hand, PAm is superior in alkali resistance to CTA but inferior in chlorine resistance. With these films, organic and inorganic deposits are generated on the film surface (fouling) with use, and there is a problem that the water permeation performance deteriorates. In general, there is a method of removing fouling by immersing the film in a solution containing acid, alkali, or chlorine. However, CTA is not resistant to alkali, and PAm is not resistant to chlorine. The invention of a film excellent in chemical resistance was expected.

  In general, polysulfone and polyethersulfone-based materials generally have hydrophobicity and thus have a characteristic of poor intermolecular cohesion. For this reason, even if the membrane is formed using the non-solvent induced phase separation (NIPS) method and the thermally induced phase separation (TIPS) method, the ultrafiltration membrane (UF, pore diameter is several tens nm to several hundreds nm) The above pores are generated. Therefore, the problem that the function as a nanofiltration membrane cannot be expressed arises. Therefore, the present inventors have come up with the idea of covalently bonding a group having an interaction force in order to increase the intermolecular force. Specifically, a group having a negative charge is preferable as a group for copolymerization. For example, a carboxyl group, a phosphoric acid group, a sulfonic acid group, and the like. According to the study by the present inventors, it has been found that a sulfonic acid group exhibits particularly high effects.

  Furthermore, it is necessary to satisfy two conflicting requirements of excluding salt penetration while ensuring water permeability. In this case, the amount and arrangement of the sulfonic acid groups are important. When water molecules permeate through the membrane, they are sequentially permeated by being attracted by the chemical capacity of the sulfonic acid group. At this time, the distance between the sulfonic acid group and the water molecule is important. That is, even if the density of the sulfonic acid group is high, if the water molecule is not easily accessible to the sulfonic acid group, the sulfonic acid group cannot exert its acceptability, and as a result, water penetration does not reach the target and The amount becomes smaller. In other words, simply increasing the number ratio of sulfonic acid groups in the molecule does not solve the problem. It is necessary to optimize the density and distribution of sulfonic acid groups in the entire membrane structure.

  In order to solve this problem, the present inventors have found a method capable of controlling the distribution of the sulfonic acid group described above by adjusting the solidification conditions of the membrane. Furthermore, it has been found that the acceptability of the sulfonic acid group can be measured using a nuclear magnetic resonance spectrum (NMR). In general, when proton NMR is measured, if a water molecule interacts with another chemical species, the density of electrons existing around the proton in the water molecule changes. The degree of change can be measured by chemical shift.

  Based on the above findings, the separation membrane of the present invention is selected from a sulfonated polyarylene ether sulfone polymer having higher alkali resistance and chlorine resistance than CTA and PAm as a material, and then the sulfonic acid group of this polymer is selected. When water molecules in a water-containing film are measured by proton NMR so that water molecules can interact well when water is contained, the chemical shift A (ppm) at the top of the spectrum peak derived from bound water and the spectrum peak derived from bulk water The greatest characteristic is that the relationship with the top chemical shift B (ppm) was controlled so as to satisfy B−0.30 ≦ A <B−0.14. From this standpoint, there has never been a material that combines salt removal and water permeability while designing a material polymer for a separation membrane while maintaining chemical resistance.

The separation membrane of the present invention is a separation membrane for the purpose of nanofiltration, and is used in a method for obtaining purified water or concentrated water by applying a pressure not lower than the osmotic pressure to the water to be treated. Specifically, desalination of pharmaceutical processes, water purification applications such as removal of agricultural chemicals and low molecular weight substances, concentration of fruit juice and fungal product, 2 stage RO treatment (boron removal) and RO pretreatment (cause of scale) To remove divalent ions). The nanofiltration pressure is generally as low as 0.3 to 1.5 MPa. As the salt removal property and water permeability of the separation membrane required for nanofiltration, generally, the salt removal rate when using NaCl is 5% or more and less than 93%, and the water permeability is 250 L / m ² / D or more. Is preferred.

  As the separation membrane of the present invention, a hollow fiber membrane or a flat membrane is used. The hollow fiber membrane is generally formed of a hollow thread formed by discharging a polymer using a tube-in-orifice type nozzle or an arc type (three-point bridge) nozzle and then solidifying the polymer. The hollow fiber membrane generally takes the form of an asymmetric membrane made of a single material. Further, the hollow fiber membrane has an advantage that the module can be made compact because the effective membrane area per unit volume in the pressure vessel (module) can be larger than that of the flat membrane. However, since the inside of the hollow fiber membrane becomes difficult to recover, it is often used with an external pressure type. On the other hand, a flat membrane is a film-shaped membrane having a structure in which a laminated film made of polyester taffeta, polysulfone, or the like is used for a support layer, and polyamide, sulfonated polysulfone, or the like is laminated thereon as a separation functional layer. Is common. The module is mainly a spiral type. As the separation membrane of the present invention, it is preferable to use a hollow fiber membrane that has a large membrane area per module volume and is unlikely to contain foreign substances on the permeate side. The hollow fiber membrane is designed so as to have a predetermined salt removal rate and permeability according to the application, and to reduce the change with time of the membrane.

The separation membrane of the present invention comprises a sulfonated polyarylene ether sulfone polymer containing a constituent represented by the following general formula [I].
In the formula, X is H or a monovalent cation species, and n is an integer of 10 to 50. Although it does not specifically limit as monovalent | monohydric cation seed | species, Sodium, potassium, lithium, another metal seed | species, various amines, etc. are mentioned.

  The sulfonated polyarylene ether sulfone polymer used in the present invention uses a monomer (3,3′-disulfo-4,4′-dichlorodiphenylsulfone derivative) in which a sulfonic acid group is introduced onto an electron-withdrawing aromatic ring. By synthesizing polyarylene ether, it is a polymer in which sulfonic acid groups are not easily removed even at high temperatures, and 2,6-dichlorobenzonitrile is used in combination with 3,3′-disulfo-4,4′-dichlorodiphenylsulfone derivatives. Thus, there is a feature that a polyarylene ether compound having a high degree of polymerization can be obtained in a short time even when a 3,3′-disulfo-4,4′-dichlorodiphenylsulfone derivative having low polymerizability is used. The sulfonated polyarylene ether sulfone polymer is particularly excellent in chemical resistance (alkali resistance and chlorine resistance), and has little change with time for long-term use of the membrane.

  The sulfonated polyarylene ether sulfone polymer can be obtained by a conventionally known method. For example, the sulfonated polyarylene ether sulfone polymer is polymerized by an aromatic nucleophilic substitution reaction including the left compound of the general formula [I] and the right compound as monomers. Can be obtained. In the case of polymerization by aromatic nucleophilic substitution reaction, the activated difluoroaromatic compound and / or dichloroaromatic compound and aromatic diol containing the compound on the left side and the compound on the right side of the above general formula [I] are converted into basic compounds. The reaction can be carried out in the presence. The polymerization can be carried out in the temperature range of 0 to 350 ° C., but is preferably 50 to 250 ° C. When the temperature is lower than 0 ° C., the reaction does not proceed sufficiently, and when the temperature is higher than 350 ° C., the polymer tends to be decomposed. The reaction can be carried out in the absence of a solvent, but is preferably carried out in a solvent. Examples of the solvent that can be used include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, diphenyl sulfone, sulfolane, and the like. And any solvent that can be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents may be used alone or as a mixture of two or more. Examples of the basic compound include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like, and those that can convert an aromatic diol into an active phenoxide structure may be used. It can use without being limited to. In the aromatic nucleophilic substitution reaction, water may be generated as a by-product. In this case, regardless of the polymerization solvent, water can be removed from the system as an azeotrope by coexisting toluene or the like in the reaction system. As a method for removing water out of the system, a water absorbing material such as molecular sieve can also be used. When the aromatic nucleophilic substitution reaction is carried out in a solvent, it is preferable to charge the monomer so that the resulting polymer concentration is 5 to 50% by weight. When the amount is less than 5% by weight, the degree of polymerization tends to be difficult to increase. On the other hand, when the amount is more than 50% by weight, the viscosity of the reaction system becomes too high, and the post-treatment of the reaction product tends to be difficult. After completion of the polymerization reaction, the solvent is removed from the reaction solution by evaporation, and the residue is washed as necessary to obtain the desired polymer. In addition, the polymer can be obtained by precipitating the polymer as a solid by adding the reaction solution in a solvent having low polymer solubility, and collecting the precipitate by filtration.

  The logarithmic viscosity of the sulfonated polyarylene ether sulfone polymer is preferably 1.0 to 2.3 dL / g. If the logarithmic viscosity is less than 1.0 dL / g, the membrane when formed into a separation membrane tends to be brittle, and if it is greater than 2.3 dL / g, it becomes difficult to dissolve the polymer, resulting in problems in workability. There is a fear.

  The sulfonic acid group content of the sulfonated polyarylene ether sulfone polymer is preferably 0.5 to 2.3 meq / g. If the sulfonic acid group content is less than 0.5 meq / g, there is a risk that the salt removal property or water permeability will not be sufficient as the separation membrane. If the content is more than 2.3 meq / g, the separation membrane swells at high temperature and high humidity. May become unsuitable for use.

The separation membrane using the polymer material of the present invention is a chemical shift A at the top of a spectrum peak derived from bound water in a proton nuclear magnetic resonance (NMR) spectrum obtained by measuring water molecules in the membrane using the water-containing membrane. (Ppm) and the chemical shift B (ppm) of the spectral peak top derived from bulk water is controlled to satisfy B−0.30 ≦ A <B−0.14. Here, bound water is a water molecule that forms a solvation by interacting with a charged group or a polar group in the micropores of the separation membrane, and its rotational and translational motion is limited. On the other hand, bulk water (also referred to as free water) maintains a normal liquid state and takes a state of high mobility that performs rotation and translation. Regarding chemical shift (chemical shift), in the case of proton NMR, when external energy (radio wave) is applied to a measurement object in a magnetic field, the density of electrons existing around the hydrogen atom of the measurement object depends on the magnitude of the electron. Although the amount of external energy absorbed is different, this difference is expressed as a difference (chemical shift difference) in the appearance location of the NMR spectrum peak. If the electron density is high, the shielding effect against external energy is high, and a spectrum peak appears on the high magnetic field side (side with a low ppm value). If the electron density is small, the shielding effect is small, and a spectrum peak appears on the low magnetic field side (the side with the large ppm value). Therefore, the magnitude of the electron density represents the magnitude of the chemical interaction that the chemical shift of proton NMR of water molecules in the film undergoes. The nanofiltration membrane made of the polymer represented by the general formula [I] has a sulfonic acid group, and the bound water is considered to particularly strongly interact with this group. The electron density of sulfonic acid group is larger than that of bulk water, and the electron density around bound water that forms strong interaction is considered to be slightly higher than that of bulk water. Therefore, the chemical shift of bound water appears on the higher magnetic field side than bulk water. The proton NMR measurement method for water molecules present in the membrane is as follows. A hollow fiber membrane sample previously immersed in distilled water for 10 minutes at room temperature (25 ° C.) is cut to a length of about 5 cm, and four samples are inserted into a capillary tube having a diameter of 3 mm. The moisture content of the sample at this time is about 300 to 400% by weight. The capillary tube is inserted into an NMR tube having a diameter of 5 mm, and proton NMR measurement is performed with an AVANCE 500 manufactured by BRUKER (resonance frequency 500.13 MHz, temperature 30 ° C., FT integration 16 times, waiting time 21 seconds). (Shim adjustment is performed in advance with heavy water (D ₂ O).)

  FIG. 1 shows an example of a proton NMR spectrum chart. Of the two spectral peaks observed at this time, the spectral peak appearing on the low magnetic field side is derived from bulk water, and the peak top of this chemical shift is set to 5.24 ppm as a reference. And the chemical shift of the peak top of the spectrum peak derived from the bound water which appears on the high magnetic field side, and those distances are confirmed. The peak top is the highest position of the spectrum peak obtained as a result of NMR measurement.

  When the peak top A (ppm) of the chemical shift derived from the bound water is A <B-0.30 with respect to the peak top B (ppm) of the chemical shift derived from the bulk water, the membrane structure as a whole is extremely dense. However, while the salt removability is approximately 93% or more, the water permeability is remarkably lowered, which is not practical. Similarly, when B> A ≧ B−0.14, the salt removability may be remarkably low or may not be expressed.

  Next, the chemical interaction between the water molecules in the separation membrane of the present invention and the polymer chains constituting the membrane molecules and the relationship with the membrane performance will be described. In general, membranes in use as spin-up and separation membranes generally have a moisture content of 50% to 1000% in the membrane. If the moisture content in this range is maintained, the chemical shift between the spectral peak tops in the proton NMR of bulk water and bound water is almost constant regardless of the moisture content. At this time, all water molecules in the separation membrane do not chemically interact with the polymer chains constituting the membrane. According to the study by the present inventors, the presence or absence of an interaction can be distinguished by measuring proton NMR of water molecules. When the membrane is approximately the above-mentioned moisture content, it does not depend on the magnitude of the moisture content, and the bulk It was found that the spectral peak appears at a position where the distance from the top of the spectral peak of water is stable and fixed. More specifically, the relationship between the chemical shift A (ppm) of the spectral peak top derived from bound water and the chemical shift B (ppm) of the spectral peak top derived from bulk water is B−0.30 ≦ A <B−0. It was found that one or more peaks were observed in a range satisfying 14. This means that there are multiple states of water in the membrane. From this, it has been found that the water in the membrane is composed of water subjected to some chemical interaction (bound water) in addition to bulk water.

According to the study by the present inventors, it has been found that there is a strong correlation between the concentration of the polymer solution subjected to spinning, the above-described chemical shift, and the physical property value. That is, when the aforementioned polymer was used as a separation membrane, proton NMR was measured using a hollow fiber membrane (hydrated state) made at a lower concentration than the polymer concentration of 25% by weight. However, the chemical shift of water molecules in the film appears in the range of B ≧ A ≧ B−0.14 (ppm). Furthermore, a membrane produced under such conditions may not show a salt removal rate when evaluated with NaCl, or may be 5% or less, and the strength of the hollow fiber membrane may be reduced, causing a problem with pressure resistance. In many cases, it does not function as a practical nanofiltration membrane. On the other hand, when the polymer concentration is 32.5% by weight or more, the physical properties of the resulting film keep the salt removal rate of 93% or more. The chemical shift of the spectrum peak top of water molecules measured in the same manner is A <B-0.30 (ppm), and the water permeability is not preferable because it is 250 L / m ² / D or less.

Furthermore, the air gap length at the time of spinning also has a great influence on the arrangement of sulfonic acid groups in the membrane, and further on the change in chemical shift subjected to bound water. According to the study by the present inventors, it has been found that there is a strong correlation between the air gap length, the above-described chemical shift, and the film performance value. That is, when the proton NMR of a yarn made under the condition that the air gap length is too long and the solvent in the system is actively evaporated using a heating zone with a certain value as a boundary, The chemical shift of water molecules appears in the range of B ≧ A ≧ B−0.14 (ppm). In the hollow fiber membrane produced under such conditions, the solvent in the membrane excessively evaporates in the process of passing through the air gap. When the solvent in the system evaporates, the concentration of the polymer is increased. At the same time, aggregation of the sulfonic acid group is accelerated. The resulting sulfonic acid groups are localized. When a membrane having such a structure is used as a nanofiltration membrane, water molecules diffusing in the membrane cannot interact efficiently with sulfonic acid groups. As a result, the salt removal rate is reduced and the water permeability is reduced. Furthermore, the polymer density on the film surface side becomes very high and the structure becomes very dense. As a result, a skin layer is formed on the outermost layer of the film, and a rough structure having no separation ability is formed inside. The water permeability of such a membrane does not reach 10 L / m ² / D, the salt removal rate is less than 50%, and does not function as a practical level nanofiltration membrane.

  Although the detailed mechanism is unknown, the present inventors have found that there is a correlation between polymer concentration and membrane performance. That is, if the polymer concentration is too low, sulfonic acid group aggregation excessively proceeds as a characteristic of the membrane structure when the membrane is formed. This means that water molecules present in the membrane cannot efficiently interact with the sulfonic acid group in the aggregated structure. As a result, when used as a separation membrane, the water molecules diffusing in the membrane cannot efficiently interact with the sulfonic acid group, so that the diffusion of water molecules is suppressed and the low water permeability performance remains. The chemical shift that the bound water receives is also close to the bulk water. Conversely, when the polymer concentration is increased, the size of the aggregate structure may be small, but the sulfonic acid groups are uniformly dispersed without agglomeration, which increases the probability of chemical contact and interaction with water molecules in the membrane. . As a result, since the sulfonic acid group channels are arranged so that water molecules diffuse quickly, high water permeability is obtained. The chemical shift of bound water can also be observed far away from free water. Based on such knowledge, the separation membrane of the present invention has a water permeability and a salt removal property required for nanofiltration, so that the position of the peak top of proton NMR derived from bound water in the membrane at the time of hydration is as follows. The relation between the chemical shift A (ppm) of the spectral peak top derived from bound water and the chemical shift B (ppm) of the spectral peak top derived from bulk water satisfies B−0.30 ≦ A <B−0.14. Is set.

  Next, the method for producing a separation membrane of the present invention will be described by taking a hollow fiber membrane as an example. The hollow fiber membrane of the present invention is prepared by discharging a membrane-forming stock solution from a spinneret through an aerial running section into a coagulation bath in the same manner as a conventionally known method, creating a hollow fiber membrane, and washing the hollow fiber membrane with water. It can be produced by subjecting it to a hydrothermal treatment to shrink the membrane.

  As the membrane-forming stock solution, a membrane material containing a polymer represented by the formula [I], a solvent and a non-solvent is used, and if necessary, an organic acid and / or an organic amine is added. The solvent is preferably one or more selected from N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and N, N-dimethylsulfoxide. More preferred is N-methyl-2-pyrrolidone. The non-solvent is preferably one or more selected from ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol. More preferably, it is ethylene glycol. The organic acid is preferably an amino acid, an aromatic carboxylic acid, a hydroxy acid, an alkoxy acid, a dibasic acid or a hydroxy monoester thereof. More preferably, it is phthalic acid, tartaric acid, ε-amino-n-caproic acid, benzoic acid, 4-methylaminobutyric acid, p-oxybenzoic acid, maleic acid, and a mixture of two or more can be used. . As the organic amine, any of primary, secondary, and tertiary hydroxyalkylamine can be used. Specifically, monoethanolamine, triethanolamine, diisopropanolamine, and triisopropanolamine are preferable.

  The concentration of the polymer of the formula [I] in the film forming stock solution is preferably 30% by weight to less than 32.5% by weight. When the concentration of the polymer is lower than the above range, the obtained hollow fiber membrane may not satisfy the pressure resistance required for nanofiltration, and when it is higher than the above range, it may not satisfy practical water permeability. . Further, the weight ratio of the solvent / non-solvent in the membrane forming stock solution is preferably 95/5 to 70/30, and more preferably in the range of 90/10 to 75/25. If the solvent / non-solvent weight ratio is lower than the above range, solvent evaporation does not proceed, the membrane surface structure does not become dense, and the water permeability does not change greatly, but the salt removal performance is low, and if it is higher than the above range, There is a possibility that the film strength cannot be obtained due to the progress of extreme asymmetric film formation.

  Next, the film-forming stock solution obtained as described above is dissolved by heating to 90 to 190 ° C., and the obtained film-forming stock solution is heated to 150 to 180 ° C. Or extruded from a tube-in orifice type nozzle. When a tube-in-orifice type nozzle is used, air, nitrogen, carbon dioxide, argon or the like is preferably used as the hollow forming material, but an organic solvent having a boiling point higher than the spinning temperature can also be used. The extruded film-forming stock solution passes through the aerial traveling part (gas atmosphere, air gap) for 0.02 to 0.4 seconds, and is then immersed in an aqueous coagulation bath to be solidified.

  As already described, in order for the sulfonic acid groups of the material polymer and water molecules to interact well, it is necessary to distribute the sulfonic acid groups uniformly in the membrane. For this purpose, the setting of the air gap length is also important. Here, the air gap refers to a space existing between the spinning nozzle and the coagulation bath in dry and wet spinning. That is, if the air gap length is as long as 100 cm, the hollow fibers spun from the nozzle through the air gap evaporate while running and the sulfonic acid groups aggregate in the membrane. In addition, when the air gap is too short as less than 0.5 cm, the unstable state of the solution after the spinneret is discharged is fixed by solidification, which is not preferable. It is not preferable to create a film by eliminating the air gap and immersing the spinneret in the coagulation liquid because the strength is insufficient. A preferable air gap length is 50 cm to 1 cm, more preferably 30 cm to 2 cm.

  It is preferable to use a coagulation bath having the same composition as the solvent and non-solvent used in the film-forming stock solution. The composition ratio of the coagulation bath is preferably solvent: non-solvent: water (weight ratio) = 0 to 15: 0 to 8: 100 to 77. If the water ratio is too low, phase separation of the membrane proceeds and the pore size may become too large.

  The hollow fiber membrane pulled up from the coagulation bath is washed away with residual solvent or non-solvent with water or salt water. As a water washing method, for example, a multi-stage inclined water washing method in which washing water is allowed to flow down in a long slanted basin, and the water is washed through the hollow fiber membrane in the rinsing water. In a Nelson roller that rolls up the yarn membrane multiple times, the surface of the Nelson roller is always wetted with water, and the water is washed by contact with the water and the hollow fiber membrane. There are a net shower water washing method in which the hollow fiber membrane is directly submerged in the deep bath water, and the like.

  The hollow fiber membrane subjected to the water washing treatment is preferably immersed in water in an unstrained state and subjected to hot water or hot salt water treatment (annealing treatment) at 70 to 98 ° C. for 5 to 60 minutes. By performing the hydrothermal treatment, it is possible to fix the membrane structure, improve the dimensional stability, and improve the thermal stability. For this purpose, the annealing treatment is usually performed at a temperature higher than the glass transition temperature and lower than the melting point. The structure of the membrane, particularly the arrangement of sulfonic acid groups, is almost determined by the dope concentration and the air gap length, but is not necessarily arranged at the most stable position. The annealing treatment has an effect of bringing the position of the molecular chain constituting the film to an optimal place including the arrangement of the sulfonic acid group in the film.

  If the hydrothermal treatment temperature is higher than the above range, the membrane structure may become too dense and the balance between salt removal and water permeability may be lost. Conversely, if the temperature is lower than the above range, the asymmetry of the membrane structure is sufficient. In addition, the desired salt removal performance may not be obtained. The hot water treatment time is usually 5 to 60 minutes. If the treatment time is too short, a sufficient annealing effect may not be obtained. In addition, non-uniformity may occur in the film structure. If the treatment time is too long, not only will the production cost increase, but the membrane may become too dense, and the desired performance balance may not be obtained.

  The hollow fiber membrane of the present invention obtained as described above is incorporated as a hollow fiber membrane module by a conventionally known method. For example, 45 to 180 hollow fiber membranes are collected into one hollow fiber membrane assembly, and a plurality of these hollow fiber membrane assemblies are arranged side by side as a flat hollow fiber membrane bundle. Wrap while traversing the core tube with holes. The winding angle at this time is set to 5 to 60 degrees, and the winding body is wound up so that the intersecting portion is formed on the peripheral surface of the specific position. Next, after bonding both ends of the wound body, only one side or both sides are cut to form a hollow fiber opening to form a hollow fiber membrane element. The obtained hollow fiber membrane element is inserted into a pressure vessel to assemble a hollow fiber membrane module.

  The inner diameter of the hollow fiber membrane is preferably 70 to 100 μm. When the inner diameter is smaller than the above range, the pressure loss of the fluid flowing through the hollow portion is generally large, so that when the length of the hollow fiber membrane is relatively long, a desired permeate amount cannot be obtained at the working pressure in nanofiltration treatment. there is a possibility. On the other hand, when the inner diameter is larger than the above range, the hollow ratio and the module membrane area are in balance, and either the pressure resistance or the membrane area per unit volume needs to be sacrificed.

  The outer diameter of the hollow fiber membrane is preferably 140 to 175 μm. If the outer diameter is smaller than the above range, the inner diameter inevitably becomes smaller, so the same problem as the above-mentioned inner diameter occurs. On the other hand, if the outer diameter is larger than the above range, the membrane area per unit volume in the module cannot be increased, and the compactness that is one of the merits of the hollow fiber type module is impaired.

  The length of the hollow fiber membrane is preferably 20 to 300 cm. This length is a range that may be commonly used in hollow fiber modules. However, if the length deviates from the above range, it may be difficult to achieve both water permeability and salt removability at a low operating cost.

  The separation membrane of the present invention is characterized in that no crystallization peak is observed in observation by differential scanning calorimetry. This is because the polymer main chain contains many ether bonds as shown in the formula [I], the main chain has high thermal mobility, and has a hydrophobic segment with low intermolecular cohesion. This is thought to be because the aggregated structure leading to is not expressed. Further, when the separation membrane of the present invention is a hollow fiber membrane, there is a feature that pores having a diameter of 10 nm or more are not observed in a film thickness portion within 1 μm from the outer peripheral portion of the hollow fiber membrane. In general, in a hollow fiber solution immersed in a coagulating liquid through an air gap, desolvation occurs from the outermost surface side of the hollow fiber membrane, and phase separation occurs immediately. Since a short structure is formed, a fine structure is formed, and the phase separation time becomes longer toward the inner side (thickness direction), and a structure in which the inner side is rougher than the surface side tends to be formed. In particular, the polymer represented by the formula [I] has a sulfonic acid group and interacts with each other through sulfonic acid groups or water molecules. Accordingly, the structure on the outermost surface side of the hollow fiber membrane acts in the direction of further densification, and as a result, the pore diameter on the membrane surface side is remarkably reduced.

  The separation membrane of the present invention has a yield strength in a wet state of 5 MPa or more and less than 9 MPa. In general, for nanofiltration, it is necessary to apply an external pressure equal to or higher than the osmotic pressure of water to be treated (for example, about 0.04 MPa when the salt concentration of a solution of sodium chloride is 500 ppm), which is practical. In order to obtain the amount of water permeation, it is necessary to apply an external pressure in the range of 0.5 to 1.5 MPa, preferably in the range of 0.5 to 1.5 MPa, considering the membrane characteristics of the formula [I]. As a result of the study by the present inventors, it has been found that there is a correlation between the pressure resistance of the hollow fiber membrane and the yield strength in the tensile direction in a wet state. Generally, in order to use a hollow fiber membrane as a nanofiltration membrane, it is preferable that the yield strength is 3 MPa or more, preferably 5 MPa or more. A hollow fiber membrane having a yield strength less than the above may not be able to withstand the external pressure of nanofiltration. In the hollow fiber membrane made of the polymer of the formula [I], when the yield strength is less than 5 MPa, the yarn shape slightly deforms within the practical external pressure range of the nanofiltration treatment, and the water permeability tends to deteriorate. It is not preferable. Moreover, in order to give pressure resistance of 9 MPa or more, it is necessary to increase the polymer concentration of the spinning dope, but this range is not preferable because the water permeability of the hollow fiber membrane may be lowered. As a result of intensive studies by the present inventors, the yield strength in a wet state is 5 MPa or more in order to use the polymer of formula [I] and operate as a nanofiltration membrane while expressing practical salt removal and water permeability. It has been found that the pressure is preferably less than 9 MPa.

Moreover, it is desirable that the yield strength is maintained even after the film is exposed to the chemical solution. When the membrane is actually used, it is necessary to periodically clean it with a chemical solution in order to maintain the membrane performance. At this time, it is preferable that the decrease in pressure resistance and salt removal performance is small even after the membrane is exposed to the chemical solution. The nanofiltration membrane of the present invention is used for water purification such as desalination of pharmaceutical processes, removal of agricultural chemicals and low molecular weight substances, concentration of fruit juice and fungal product, 2 stage RO treatment (boron removal) and RO pretreatment ( (Removal of divalent ions causing scale) Since it is assumed to be used in applications, there is almost no decrease in the salt removal performance of the membrane, and the strength retention of the membrane is 80% or more, preferably 90% or more More preferably, it is 95% or more. When the strength retention is smaller than these, the hollow fiber membrane cannot withstand the operation pressure outside the nanofiltration, the shape of the yarn changes, and the water permeability and salt removability may deteriorate. The present inventors investigated about chlorine resistance and alkali resistance using the hollow fiber membrane which consists of a polymer of a formula [I]. As a result, both when the membrane was immersed using a chlorine solution adjusted to a free chlorine concentration of 100 ppm, pH 7, and about 20 ° C., and when the membrane was immersed using an alkaline solution adjusted to pH 10 and 40 ° C. , The salt removal performance hardly changed even after 12 weeks, and the yield strength retention was found to be 98% or more. The yield strength retention rate is as follows.
Yield strength retention (%) = (yield strength of hollow fiber membrane before immersion [MPa] / yield strength of hollow fiber membrane after immersion [MPa]) × 100

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, the measurement of the characteristic value measured in the Example followed the following method.

(1) Logarithmic viscosity The polymer powder was dissolved in N-methyl-2-pyrrolidone at a concentration of 0.5 g / dl, and the viscosity was measured using a Ubbelohde viscometer in a constant temperature bath at 30 ° C. (ta / tb] / c) (ta is the number of seconds that the sample solution falls, tb is the number of seconds that the solvent is dropped, and c is the polymer concentration).

(2) Sulfonic acid group content The sample dried overnight under a nitrogen atmosphere was weighed, stirred with an aqueous sodium hydroxide solution, and then back titrated with an aqueous hydrochloric acid solution to determine the ion exchange capacity (IEC). .

(3) n in formula [I]
A polymer solution prepared by dissolving 20 mg of a polymer dried overnight in a vacuum drier previously adjusted to 100 ° C. in 1 mL of deuterated DMSO (DMSO-D6) manufactured by Nacalai Tesque Co., Ltd. was used. Proton NMR was measured at 13 MHz, temperature 30 ° C., and FT integration 32 times. In the obtained spectrum chart, spectral peaks corresponding to protons a and b on the aromatic ring of the formula [I] shown below are independent, and the ratio of these integrated intensities is as shown in the following formula.
Integral intensity a: Integral intensity b = n: (100−n)
In Formula [I], protons a and b on the aromatic ring for evaluating n are shown.

(4) Moisture content About 1 g of wet hollow fiber was weighed with an electronic balance, and dried in a vacuum dryer overnight adjusted to 100 ° C. overnight. The dried hollow fiber membrane was weighed with an electronic balance, and the moisture content was calculated using the following equation.
Moisture content (%) = (weight of hollow fiber membrane after drying [wt%] / weight of hollow fiber membrane before drying [wt%]) × 100

(5) Chemical shift A hollow fiber membrane sample previously immersed in distilled water for 10 minutes at room temperature (25 ° C.) was cut to a length of about 5 cm, and four samples were inserted into a glass capillary tube having a diameter of 3 mm. . The moisture content of the sample at this time was about 300 to 400% by weight. The capillary tube was inserted into an NMR tube having a diameter of 5 mm, and proton NMR measurement was performed with an AVANCE 500 manufactured by BRUKER (resonance frequency 500.13 MHz, temperature 30 ° C., FT integration 16 times, waiting time 21 seconds). (The shim was adjusted beforehand with heavy water (D ₂ O).)
FIG. 1 shows an example of a proton NMR spectrum chart. Of the two observed spectral peaks, the spectral peak appearing on the low magnetic field side was derived from bulk water, and the peak top of this chemical shift was adjusted to 5.24 ppm as a reference. And the chemical shift of the peak top of the spectrum peak derived from the bound water which appears on the high magnetic field side, and those distances were confirmed. All chemical shift values were read from the peak top value of the spectrum peak.

(5) Observation of pores The hollow fiber membrane was immersed in liquid nitrogen and frozen, and the cross section of the hollow fiber membrane and the surface of the hollow fiber membrane were fixed to a sample stage for SEM observation with a double-sided tape. These samples were coated with platinum and observed at a magnification of 10,000 using a scanning electron microscope (S-800) manufactured by Hitachi. At this time, the presence or absence of pores having a diameter of 10 nm or more was confirmed in the film thickness portion within 1 μm from the outer peripheral portion of the hollow fiber membrane.

(6) Crystallization peak A hollow fiber membrane sample previously dried in a vacuum dryer at 60 ° C was used, and a differential scanning calorimeter (DSC Q100) manufactured by TA instruments was used as a modulation temperature condition under nitrogen for a period of 60 seconds. The temperature was raised at a rate of 5 ° C./min with an amplitude of ± 0.796 ° C. and a temperature range of 20 ° C. to 250 ° C. From the irreversible component obtained as a result of the measurement, the presence or absence of an exothermic peak derived from crystallization was confirmed.

(7) Outer diameter / inner diameter of hollow fiber membrane Using a 2 mm thick SUS platelet with a 3 mmφ hole, the hole is filled with an appropriate amount of wet hollow fiber membrane and cut to expose the cross section of the hollow fiber membrane. A sample holder was created. This was placed on the stage of a Nikon microscope (ECLIPSE LV100), and then a Nikon image processing apparatus (DIGITAL SIGN DS-U2) and a CCD camera (DS-Ri1) were activated. Using NIS Element D3.00 SP6 as image analysis software, calculate the outer diameter and inner diameter of the hollow fiber membrane by measuring the outer diameter and inner diameter of the cross section of the hollow fiber membrane displayed on the screen using the measurement function of the analysis software. did.

(8) Yield strength A tensile test of a wet hollow fiber membrane was performed using SHIMADZU AGS-J 1 kN manufactured by Shimadzu Corporation. The load cell was 50 N, and a flat chuck was used for fixing and pulling the yarn. The initial gripping distance between the chucks was set to 50 mm, and the weight applied to the yarn when threading the flat chuck was set to 0.03N. The yarn pulling speed was 50 mm / min. For the measurement data, stress (MPa), elongation (%), and yield strength (MPa) were calculated using analysis software (TRAPEZIUM X ver. 1.0.2.SP).

(9) Yield strength retention (chlorine resistance, alkali resistance)
A sodium hypochlorite solution of Nacalai Tesque was diluted with distilled water to a free chlorine concentration of 100 ppm, and a chlorine solution adjusted to pH 7 using 1N hydrochloric acid of the company was prepared. In addition, an alkaline solution having a pH of 10 was prepared by diluting the 1N sodium hydroxide aqueous solution of the company with distilled water. A hollow fiber membrane having 20 bundles each having a length of 20 cm was immersed in these. The temperature of the aqueous chlorine solution was room temperature (about 20 ° C.), and the temperature of the alkaline solution was 40 ° C. After soaking for 12 weeks while keeping the free chlorine concentration and pH constant, the yield strength of the soaked yarn was measured by the same method as the above-described measurement of the yield strength. The formula for calculating the yield strength retention rate is as follows.
Yield strength retention (%) = (yield strength of hollow fiber membrane before immersion [MPa] / yield strength of hollow fiber membrane after immersion [MPa]) × 100

(10) Water permeability After hollow fiber membranes were bundled and inserted into a plastic sleeve, a thermosetting resin was poured into the sleeve, cured and sealed. The end portion of the hollow fiber membrane cured with the thermosetting resin was cut to obtain an opening surface of the hollow fiber membrane, and an evaluation module having an outer diameter reference membrane area of approximately 0.025 m ² was produced. This evaluation module was connected to a membrane performance testing device consisting of a feed water tank and a pump, and the performance was evaluated.
The supply aqueous solution having a sodium chloride concentration of 500 mg / L is filtered from the outside to the inside of the hollow fiber membrane at 25 ° C. and a pressure of 1.0 MPa, and the apparatus is operated for about 1 hour. Thereafter, the membrane permeate was collected from the opening surface of the hollow fiber membrane, and the weight of the permeate was measured with an electronic balance (Shimadzu Corporation LIBBROR EB-3200D). The permeated water weight was converted to the permeated water amount at 25 ° C. by the following formula.
Permeated water amount (L) = Permeated water weight (kg) /0.99704 (kg / L)
The water permeability (FR) is calculated from the following formula.
FR [L / m ² / day] = permeated water amount [L] / outer diameter reference membrane area [m ² ] / collection time [min] × (60 [min] × 24 [hour])

(11) Salt removal rate Using a conductivity meter (Toa DKK Corporation CM-25R) from the membrane permeate collected in the water permeation measurement and a sodium chloride concentration 500 mg / L aqueous solution used in the same water permeation measurement. Sodium chloride concentration was measured.
The salt removal rate is calculated from the following formula.
Salt removal rate [%] = (1-membrane permeated water salt concentration [mg / L] / feed aqueous solution salt concentration [mg / L]) × 100

Example 1
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 11.5 mol%, 2,6-dichlorobenzonitrile (abbreviation: DCBN) 38.5 mol%, 4,4 A sulfonated polyarylethersulfone-based polymer (abbreviation: SPN-23) obtained by polymerizing 50 mol% of -biphenol was dried in advance at 110 ° C. for 12 hours, and then weighed 66 parts by weight, followed by N-methyl- 2-Pyrrolidone (abbreviation: NMP) 123.2 parts by weight and ethylene glycol (abbreviation: EG) 30.8 parts by weight were charged into a separable flask and stirred at 170 ° C. for 3 hours to obtain a uniform polymer concentration of 30% by weight. A polymer solution was obtained.
This polymer solution was used as a spinning raw material (dope) and charged into a spinning device having a plunger-type extrusion function. The dope was kept at 150 ° C. and fed to a tube-in-orifice nozzle, and discharged from a dope discharge hole having a slit width of 100 microns (outer diameter 400 microns, inner diameter 200 microns) at a rate of 0.24 g / min. EG was used as the internal liquid, and the liquid was fed at a rate of 0.12 g / min with a gear pump, and discharged from a 110 micron internal liquid discharge hole. The air gap length was 20 mm, and it was immersed in a coagulation bath made of pure water. The coagulated hollow fiber membrane was taken up at a spinning speed of 15 m / min and wound up with a skeiner or a winder. Further, the obtained hollow fiber membrane sample was further immersed in a salt water having a concentration of 4.5% by weight, and annealed at a temperature of 98 ° C. for 20 minutes. The details of the membrane and the evaluation results are shown in Table 1.

(Example 2)
By immersing the hollow fiber membrane obtained in Example 1 in a 10 wt% aqueous lithium chloride solution overnight, the counter cation (X) on the sulfonic acid group of the formula [I] was changed to lithium ions. The details of the membrane and the evaluation results are shown in Table 1.

(Example 3)
By immersing the hollow fiber membrane obtained in Example 1 in a 10 wt% aqueous potassium chloride solution overnight, the counter cation (X) on the sulfonic acid group of the formula [I] was changed to potassium ions. The details of the membrane and the evaluation results are shown in Table 1.

Example 4
3,3′-disulfo-4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: S-DCDPS) 11.5 mol%, 2,6-dichlorobenzonitrile (abbreviation: DCBN) 38.5 mol%, 4,4 A sulfonated polyarylether sulfone polymer (abbreviation: SPN-23) obtained by polymerizing 50 mol% of biphenol was immersed in 2N concentrated sulfuric acid for 24 hours, and then the polymer was washed until the water after washing became neutral. Example except that SPN-23 (X = H type) in which the counter cation on the sulfonic acid group was converted to proton by washing with water and using hot water for the annealing treatment after spinning were used. A hollow fiber membrane was obtained in the same manner as in 1. The details of the membrane and the evaluation results are shown in Table 1.

(Example 5)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that n in formula [I] was changed to 12. The details of the membrane and the evaluation results are shown in Table 1.

(Example 6)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that n in formula [I] was changed to 45. The details of the membrane and the evaluation results are shown in Table 1.

(Example 7)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the composition of the dope was 62 parts by weight of SPN-23 polymer, 110.4 parts by weight of NMP, and 27.6 parts by weight of EG. The details of the membrane and the evaluation results are shown in Table 1.

(Example 8)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the dope composition was 64 parts by weight of SPN-23 polymer, 112.9 parts by weight of NMP, and 23.1 parts by weight of EG. The details of the membrane and the evaluation results are shown in Table 1.

Example 9
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the air gap length was 10 mm. The details of the membrane and the evaluation results are shown in Table 1.

(Example 10)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the air gap length was 400 mm. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 1)
The polymer prepared in Example 1 was charged with a solvent so that the concentration was 34% by weight (including a mixed solvent of 87:13 in a weight ratio of NMP to EG), and stirred to obtain a uniform polymer solution suitable for spinning. Produced. Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 1. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 2)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the polymer concentration of the dope was changed to 27.5% by weight (including a mixed solvent of 75:25 in a weight ratio of NMP to EG). The obtained hollow fiber membrane had low yield strength and reduced water permeability. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 3)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the air gap length was 3 mm. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 4)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the air gap length was 700 mm, a tubular heater capable of heating the air in the air gap was attached, and the atmospheric temperature of the air gap was 100 ° C. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 5)
4,4′-dichlorodiphenylsulfone disodium salt (abbreviation: DCDPS) 11.5 mol%, 2,6-dichlorobenzonitrile (abbreviation: DCBN) 38.5 mol%, and 4,4′-biphenol 50 mol% were polymerized. The obtained polyarylethersulfone-based polymer was vacuum-dried at 80 ° C. for 24 hours in advance and then weighed 66 parts by weight, followed by N-methyl-2-pyrrolidone (abbreviation: NMP) 123.2 parts by weight, ethylene glycol (Abbreviation: EG) 30.8 parts by weight were put into a separable flask and stirred at 100 ° C. for 3 hours to obtain a polymer solution having a uniform concentration of 40% by weight. A hollow fiber membrane was obtained in the same manner as in Example 1 except that the dope temperature and spinning temperature of this polymer solution were changed to 60 ° C. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 6)
A hollow fiber membrane was obtained in the same manner as in Example except that a polymer having a reduced sulfonic acid group content (n = 8.9 in formula [I]) was used. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 7)
Spinning was attempted in the same manner as in Example 1 except that a polymer having an increased sulfonic acid group content (n = 52.3 in formula [I]) was used. As a result, the hollow fiber that passed through the coagulation bath swelled significantly, and a hollow fiber membrane that could withstand the evaluation of the membrane performance could not be obtained. Details of the membrane are shown in Table 1.

(Comparative Example 8)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 parts by weight, NMP 49.9 parts by weight, EG 8.8 parts by weight, benzoic acid 0.3 parts by weight uniformly dissolved at 180 ° C. Got. The obtained film-forming stock solution was defoamed under reduced pressure, and then discharged from an arc type nozzle into a space (air gap, AG) that was blocked from outside air at 163 ° C., after passing through an AG passage time of 0.03 seconds, NMP : EG: water = 4.25: 0.75: 95 was immersed in a 12 ° C. coagulation bath. Subsequently, the hollow fiber membrane was washed by a multistage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber membrane was immersed in water at 60 ° C. and annealed for 40 minutes. The details of the membrane and the evaluation results are shown in Table 1.

(Comparative Example 9)
8.062 parts by weight of anhydrous piperazine and 54.23 parts by weight of 4,4′-diaminodiphenylsulfone were charged into a 500 L reactor equipped with a nitrogen introduction tube, a thermometer and a stirrer under a nitrogen stream. Subsequently, 50 parts by weight of pyridine as an acid scavenger and 470 parts by weight of N-methylpyrrolidone (NMP) as a reaction solvent were added to the reactor and sufficiently stirred to obtain a homogeneous solution. After cooling the solution to about 5 ° C., 63.342 parts by weight of terephthalic acid dichloride was added to the solution to start a polycondensation reaction. The mixture was stirred for about 30 minutes under cooling and about 30 minutes at room temperature. After completion of the reaction, the reaction solution was poured into 1000 parts by weight of water to precipitate the polymer. Subsequently, the fineness of the produced polymer and washing of the pure product with pure water were repeated four times to remove unreacted substances and solvents in the polymer. Finally, the polymer was dried with hot air at about 80-100 ° C. for about 48 hours.
Polyamide (37 parts by weight) synthesized above, N, N-dimethylacetamide (57.11 parts by weight), 5.79 parts by weight of NMP, anhydrous polyglycerol (number average molecular weight = 480, 3.7 parts by weight), calcium chloride A film-forming stock solution (dope) composed of hexahydrate (2.75 parts by weight) is discharged from an arc (three-point bridge) type nozzle (temperature: 130 ° C.) and guided into water at about 10 ° C. A hollow fiber membrane of 165 microns and a hollow rate of about 30% was obtained. Further, for the purpose of removing the solvent and polyglycerin remaining in the membrane, the hollow fiber membrane was immersed in water all day and night. The details of the membrane and the evaluation results are shown in Table 1.

Table 1 shows details and evaluation results of the films of Examples 1 to 10 and Comparative Examples 1 to 9.

  As is clear from the results in Table 1, in Examples 1 to 10, the salt removability and water permeability at a pressure of 1.0 MPa suitable for nanofiltration treatment sufficiently satisfy the practical level. In Comparative Example 1, since the polymer concentration of the membrane forming stock solution was high, the polymer density in the hollow fiber membrane was increased as a whole. As a result, the salt removability increased but the water permeability decreased. Comparative Example 2 cannot withstand the external pressure at the time of evaluation due to lowering of the polymer concentration of the membrane-forming stock solution, and salt removal and water permeability are reduced, which is not suitable for nanofiltration treatment. In Comparative Example 3, spinning was performed with the air gap shortened to 3 mm. However, the yarn diameter of the hollow fiber membrane was not stable, and the performance also varied. In Comparative Example 4, although the air gap was 700 mm and the atmospheric temperature in the air gap was 100 ° C., the salt removal performance and water permeability were markedly reduced. In Comparative Example 5, a hollow fiber membrane made of non-sulfonated polyarylethersulfone was used, but the pore diameter in the membrane was large and salt removability was not exhibited. In Comparative Example 6, when n in the formula [I] was outside the lower limit of the range of the present invention, the water permeability increased, but the salt removability was remarkably inferior. In Comparative Example 7, when n in the formula [I] was outside the upper limit of the range of the present invention, it was difficult to obtain a hollow fiber that could be evaluated stably. In Comparative Example 8, when a hollow fiber membrane was used using cellulose triacetate, the yield strength retention rate related to alkali resistance was lowered, resulting in inferior alkali resistance. Although the comparative example 9 used the hollow fiber membrane which consists of polyamides, the yield strength retention rate regarding chlorine resistance fell remarkably, and it resulted in inferior to chlorine resistance.

  The separation membrane of the present invention is extremely useful for nanofiltration treatment because it has a high level of both salt removal and water permeability while using a material excellent in chemical resistance.

Claims (7)

Proton nuclear magnetic resonance comprising a separation membrane comprising a sulfonated polyarylene ether sulfone polymer containing a component represented by the following general formula [I], wherein water molecules in the membrane were measured using the separation membrane in a water-containing state In the spectrum, the relationship between the chemical shift A (ppm) of the spectral peak top derived from bound water and the chemical shift B (ppm) of the spectral peak top derived from bulk water satisfies B−0.30 ≦ A <B−0.14. A separation membrane for nanofiltration characterized by filling.
In the formula, X is H or a monovalent cation species, and n is an integer of 10 to 50.   The separation membrane according to claim 1, wherein the sulfonated polyarylene ether sulfone polymer has a logarithmic viscosity of 1.0 to 2.3 dL / g.   The separation membrane according to claim 1 or 2, wherein the sulfonated polyarylene ether sulfone polymer has a sulfonic acid group content of 0.5 to 2.3 meq / g.   The separation membrane according to any one of claims 1 to 3, wherein no crystallization peak is observed in observation by differential scanning calorimetry.   The separation membrane according to any one of claims 1 to 4, wherein the separation membrane is a hollow fiber membrane having an inner diameter of 70 to 100 µm and an outer diameter of 140 to 175 µm.   6. The separation membrane according to claim 5, wherein pores having a diameter of 10 nm or more are not observed in a film thickness portion within 1 μm from the outer peripheral portion of the hollow fiber membrane.   The separation membrane according to claim 5 or 6, wherein the yield strength in a wet state is 5 MPa or more and less than 9 MPa.