JP6070260B2 - Hollow fiber type semipermeable membrane, manufacturing method and module thereof - Google Patents

Description

  The present invention relates to a hollow fiber type semipermeable membrane that can maintain both water permeability and separation performance at a high level, reduce installation space, and improve processing efficiency, a method for manufacturing the same, and a module. More specifically, concentration of valuable materials, volume reduction by recovery and concentration of wastewater, or water permeation from a low-concentration aqueous solution to a high-concentration and pressurized aqueous solution as a driving force, and the permeated water Energy is generated by, for example, turning the turbine at the increased flow rate and pressure of the high-concentration and pressurized aqueous solution. In particular, it is a hollow fiber type semipermeable membrane suitably used for water treatment or the like for generating energy such as electric power by utilizing a difference in concentration between seawater or concentrated seawater and fresh water.

  Separation / concentration of liquid mixture by membrane separation is an energy-saving method because it does not involve a phase change compared to separation techniques such as distillation, and since it does not involve changes in the state of substances, it concentrates juice and separates beer enzymes. It is widely used in various fields such as food fields such as organic matter recovery from industrial wastewater, and water treatment with semipermeable membranes has become established as an indispensable process that supports state-of-the-art technology.

  For example, the generation of energy by water obtained by utilizing the difference in concentration between seawater and fresh water using a semipermeable membrane is a clean process and is expected as renewable energy. In particular, hollow fiber type semipermeable membranes have a smaller water permeability per unit membrane area than spiral type semipermeable membranes, but can take a larger membrane area per membrane module volume, so the overall water permeability must be increased. The volumetric efficiency is very high and the compactness is excellent. In addition, in the case of water treatment using a concentration difference generated by supplying both high-concentration aqueous solution and fresh water into the module and bringing them into contact with each other through a semipermeable membrane, the membrane surface is compared to the spiral type. Therefore, there is an advantage that the concentration polarization can be suppressed to be small and the decrease in the concentration difference can be suppressed.

Such a hollow fiber type semipermeable membrane is generally prepared by preparing a membrane-forming stock solution containing cellulose acetate as a polymer material, discharging it from the spinneret into the air, subsequently coagulating it in the coagulating solution, and washing it with hot water. Manufactured by processing and shrinking the membrane. For example, in the Example of Patent Document 1, a semipermeable membrane obtained by discharging and coagulating a film-forming stock solution using cellulose triacetate as a polymer material, and performing a hydrothermal treatment at 85 ° C. for 20 minutes under no tension after washing with water. Have been described. Referring to the data of this example, the water permeability of the semipermeable membrane and the removal rate of sodium chloride measured at a pressure of 30 kg / cm ² using 0.2% sodium chloride aqueous solution as the feed water are 230 l / (m ² days), respectively. 99.85% (Example 1), 245 l / (m ² days), 99.87% (Example 3), 250 l / (m ² days), 99.84% (Example 4) It is shown. Since the amount of water permeation depends on the effective pressure difference, when the effective pressure difference is low, such as when the fresh water is permeated through the semipermeable membrane of the above-described embodiment using the concentration difference as a driving force, for example, at a half pressure of 15 kg / cm ² . When measured, the removal rate of sodium chloride is not significantly affected, but the water permeability decreases to about 120 l / m ² day, which is almost half. That is, the conventional semipermeable membrane such as Patent Document 1 can exhibit a high salt removal performance because the membrane shrinkage is increased at a high hydrothermal treatment temperature, but there is a problem that the water permeability performance is lowered when used at a low pressure. When it is not preferable to apply a high pressure, such as when used for water treatment using a concentration difference as a driving force, the treatment capacity cannot be increased.

Patent Documents 2 and 3 are examples of attempts to maintain both water permeability and separation performance at a high level in a semipermeable membrane. Patent Document 2 discloses a technique related to a hollow fiber type semipermeable membrane module used for solid separation or solute separation from a liquid mixture. However, considering the hollow fiber membrane performance using cellulose triacetate in Table 1 of Patent Document 2, the water permeability (FR1) measured at an operating pressure of 55 kg / cm ² is 22.6 to 91.5 l / (m ² · And high water permeability is not achieved.

Further, Patent Document 3 discloses a flat membrane type composite semipermeable membrane having both a high salt rejection and a high permeability provided with an active layer (thin film, skin layer) mainly composed of polyamide on a microporous support. Techniques related to this are disclosed. Semipermeable membrane described in Patent Document 3, according to the description of Example 1, permeation rate measured at operating pressure 7.5 kg / cm ² is 1.0m ³ / ^{(m 2} · day) (1000l / ^{m 2}・ It is stated that the date is However, since this semipermeable membrane has a flat membrane shape, in a membrane module used for water treatment that actually uses a concentration difference through the semipermeable membrane as a driving force, a high concentration aqueous solution and a low concentration supplied to the module are used. It is difficult to distribute the aqueous solution (fresh water) effectively and uniformly on the front surface of the membrane, and the portion where the supplied aqueous solution is small has a particularly large concentration polarization on the membrane surface, so that the concentration through the membrane is effective. There are disadvantages that it is difficult to ensure the difference and the efficiency of water treatment cannot be increased. Moreover, the film made of such a polyamide material is inferior in chlorine resistance. Moreover, there is a demerit that the sterilizing chemicals that can be used are limited.

  On the other hand, from users who place importance on the economics and compactness of water treatment membrane plants, it is strongly desired to improve the treatment capacity per membrane area of the hollow fiber type semipermeable membrane. In the case of water treatment that does not apply high pressure and the concentration difference is the driving force, high water permeability cannot be obtained even if a conventional low-pressure semipermeable membrane is used, which ultimately reduces water production costs and installation space. The current situation is not possible.

  As described above, there is no cellulose acetate-based hollow fiber type semipermeable membrane that can achieve both water permeability performance and separation performance at a high level, and can efficiently perform water treatment with a small installation space.

JP 59-036715 A JP-A-10-337448 Japanese Patent Laid-Open No. 09-019630

  The present invention was devised in view of the current state of the prior art described above, and its purpose is to use different concentrations of liquid through a semipermeable membrane, and use the concentration difference between them as a driving force to reduce the low concentration side water. Achieves a high level of water permeability and separation performance that allows efficient treatment in a small membrane area and installation space in water treatment that generates energy by the flow rate and pressure of water that permeates the high concentration side. An object of the present invention is to provide a hollow fiber type semipermeable membrane, a method of manufacturing the same, and a module. In particular, the hollow fiber type semipermeable membrane of the present invention allows the semipermeable membrane to permeate from the supplied water by using as a driving force the concentration difference between water having a high salt concentration (for example, seawater, concentrated seawater) and an aqueous solution having a lower salt concentration. It is suitable for water treatment use when generating energy with water taken out.

  As a result of intensive studies to achieve the above object, the present inventor has found that the dense layer having the role of separating salt and water in the hollow fiber type semipermeable membrane is thinner than before and the concentration difference is increased by increasing the asymmetry. As a result, it was found that by obtaining a large amount of permeated water having a driving force as a driving force, water capable of generating energy and pressure can be achieved at a high level, and the present invention has been completed.

That is, the present invention has the following configurations (1) to (3).
(1) An aqueous solution having a sodium chloride concentration of 25 g at 25 ° C. and a pressure of 1.0 MPa is flowed to the outside of a hollow fiber type semipermeable membrane having a length of 70 cm, and fresh water having a sodium chloride concentration of 25 g at 0 ° C./L When flowing inside one open end of the hollow fiber type semipermeable membrane and discharging from the other open end at 10 kPa or less, the concentration difference is used as a driving force to move from the inside to the outside of the hollow fiber type semipermeable membrane. The water flow rate is 30 to 90 L / min under the condition that twice the water flow rate flowing toward the outside flows into the outside and the flow rate from the inside of the hollow fiber type semipermeable membrane is 10% of the water flow rate. The amount of water permeation when an aqueous solution of m ² / day and a sodium chloride concentration of 1.5 g / L is filtered from the outside to the inside of the hollow fiber type semipermeable membrane at 25 ° C. and a pressure of 1.5 MPa is 100 to 300 L. a hollow fiber semipermeable membrane which is / m 2 ^/ day, an outer diameter of 10 To 2 8 are 0Myu m, inner diameter of 50 to 200 [mu] m, wherein the hollow ratio is 24 to 42%, hollow fiber semipermeable membrane for water treatment for the driving force density differences.
(2) A membrane-forming stock solution containing a polymer, a solvent, and a non-solvent is prepared, and this is discharged from the spinneret through the air running part into the coagulation liquid to produce a hollow fiber type semipermeable membrane. The method for producing a hollow fiber type semipermeable membrane according to (1), which is obtained by rinsing the permeable membrane and then subjecting it to a hydrothermal treatment to shrink the membrane, wherein the polymer concentration in the membrane-forming stock solution is 40 to 45 wt. %, The solvent / non-solvent weight ratio in the membrane forming stock solution is 80/20 to 95/5, and the temperature of the hot water treatment is more than 70 ° C. and 80 ° C. or less, and the solvent It is at least one selected from N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and N, N-dimethylsulfoxide, and the non-solvent is ethylene glycol, diethylene glycol, triethylene glycol , Polyethylene Wherein the at least one selected from glycol.
(3) A hollow fiber type semipermeable membrane module comprising the hollow fiber type semipermeable membrane according to (1).

  The hollow fiber type semipermeable membrane of the present invention is designed such that the water permeability of the membrane is high and the water permeability is high when the difference in salt concentration is the driving force due to the high separation performance of water and salt. Therefore, it is possible to efficiently extract water and pressure for generating energy using the concentration difference as a driving force.

It is explanatory drawing of the manufacturing process of the semipermeable membrane of this invention.

  Conventionally, hollow fiber type semipermeable membranes, especially semipermeable membranes with high salinity and water separation, have mainly focused on the densification of the membrane structure, basically increasing the polymer concentration in the membrane forming stock solution. Development has been carried out in the direction of further tightening the membrane structure by setting and subjecting the membrane after film formation to high-temperature hydrothermal treatment. Such a method is reasonable in terms of imparting durability and high separability when used in a pressurized state of high pressure, and seawater is supplied at high pressure and filtered through a semipermeable membrane to desalinate the seawater. It is reasonable as a development oriented semi-permeable membrane. However, if a high pressure is not applied to the supply water and the concentration difference between the liquids through the semipermeable membrane is used as a driving force to divert to a semipermeable membrane for water treatment, a low effective pressure difference (osmotic pressure difference) Only a low water permeability can be obtained for the treatment.

  In order to achieve both high separation of salt and water and high water permeability, the present inventor has moved away from the development direction of the conventional semipermeable membrane and has improved the membrane structure by adopting a new membrane design concept. . In other words, separation of water and salt is achieved by increasing the asymmetry of the structure even more than the semipermeable membrane that is processed by supplying supply water at medium to high pressure, and making the separation active layer (dense layer) thin and dense. We thought that the balance of water permeability and water permeability could be improved. Moreover, it was thought that the concentration polarization of the support layer portion can be reduced and an effective concentration difference can be ensured by adopting a structure that promotes diffusion in the support layer portion. Furthermore, regarding membrane module design that exhibits maximum performance while having sufficient durability, the relationship between the flow pressure loss of the fluid flowing through the hollow part and the membrane area per module volume is outside of the hollow fiber type semipermeable membrane. We focused on optimization of diameter and hollowness. The present invention has been completed through repeated trial and error toward the realization of these technical ideas.

  The semipermeable membrane of the present invention is a hollow fiber type membrane, and it is preferable to employ cellulose acetate as a material. Cellulose acetate is resistant to chlorine, which is a bactericide, and can easily suppress the growth of microorganisms. Therefore, there is a feature that microbial contamination on the film surface can be effectively suppressed. Among cellulose acetates, cellulose triacetate is preferable from the viewpoint of durability. The hollow fiber type membrane can take more membrane area per module than the spiral type membrane, and depending on the size of the hollow fiber type semipermeable membrane, the spiral type About 10 times as large as the membrane area can be obtained. Therefore, the hollow fiber type membrane may have a very small amount of treatment per unit membrane area when obtaining the same water permeability, and can reduce the contamination of the membrane surface that occurs when the feed water permeates the membrane, and the membrane can be washed. The driving time up to can be taken longer.

  The semipermeable membrane of the present invention is a pressurized state in which water is permeated from the low concentration side to the high concentration side by using the concentration difference between the low concentration aqueous solution and the high concentration aqueous solution through the membrane as a driving force. Get the water. The method of generating energy using the obtained pressurized water is not particularly limited, but as an example, a method of rotating a turbine with a water flow, such as a water flow generator, and converting the rotation into electric power with a generator is given. It is done. Accordingly, during operation, the high concentration side is held in a pressurized state in order to turn the turbine. This pressure is smaller than the osmotic pressure difference of the concentration difference, and is usually set to about half of the osmotic pressure. This concentration difference (osmotic pressure difference) is a driving force through which fresh water permeates the membrane, and maintains the pressurized state. The value obtained by subtracting the pressure for the pressurization is obtained. The salt concentration of the high-concentration aqueous solution is typically seawater that is widely present. When seawater in a high-salt concentration region is included, it is about 3.5% to 7%. A range of about ~ 3 MPa is reasonable. On the other hand, the low-concentration aqueous solution is a concentration of 1/10 or less of general seawater, which is a typical high-concentration aqueous solution, as a salinity concentration, and 3500 mg / L or less for TDS (evaporation residue concentration). The pressure is 0.3 MPa or less. For example, river water, lake water, tap water, industrial water, wastewater treatment water, and the like correspond to this.

  Semipermeable membranes are generally classified by operating pressure, but high-pressure membranes used at operating pressures of 5-8 MPa are used for seawater desalination and are very dense to withstand pressures exceeding the osmotic pressure of seawater. It has a simple structure. On the other hand, the semipermeable membrane of the present invention allows water to permeate by using a concentration difference as a driving force, and is used at an operation pressure of 3 MPa or less, which is lower than the osmotic pressure of a high concentration side solution such as seawater. Since the conventional high pressure membrane has a relatively dense structure in order to impart pressure resistance, when the effective pressure difference is reduced, the water permeability decreases in proportion to the pressure. When the structure of the entire membrane is roughened to increase the amount of water permeation, the separability decreases. Further, the conventional low-pressure membrane does not have a structure capable of achieving high water permeability because it has been developed based on a medium-high pressure membrane. The semipermeable membrane of the present invention achieves a high level of water permeability and separability with a low effective pressure difference, and further obtains a high water permeability performance level when water is permeated through the membrane using the concentration difference as a driving force. The design philosophy does not exist in the past.

The semipermeable membrane of the present invention is an aqueous solution having a sodium chloride concentration of 35 g / L at 25 ° C. and a pressure of 1.0 MPa, which flows outside the hollow fiber type semipermeable membrane having a length of about 70 cm. When 0 g / L of fresh water is introduced from one open end of the hollow fiber type semipermeable membrane and discharged at 10 kPa or less from the other open end, the hollow fiber type semipermeable membrane is obtained using the concentration difference as a driving force. When water permeates from the inner side to the outer side, the amount of water permeation is twice the flow rate flowing to the outside of the hollow fiber type semipermeable membrane, and the opening at the other end of the hollow fiber type semipermeable membrane The water flow rate per membrane area under the condition that the flow rate discharged from the water flow rate is 10% of the water flow rate is 30 to 90 L / m ² / day, and an aqueous solution having a sodium chloride concentration of 1.5 g / L is 25 ° C. When filtering from the outside to the inside of the hollow fiber type semipermeable membrane at a pressure of 1.5 MPa Water is at 100~300L / ^{m 2} / day, an outer diameter of 100～280Myuemu, inner diameter of 50 to 200 [mu] m, hollow ratio is characterized in that it is a 24 to 42%. The sodium chloride concentration of 35 g / L is intended for use in a concentration difference between seawater and fresh water that are abundant in nature, and is in the range of 34.5 g / L to 35.4 g / L. . The sodium chloride concentration on the fresh water side of 0 g / L is assumed to be fresh water with low osmotic pressure that can be easily obtained in nature, and means 200 mg / L or less. The pressure of 1.0 MPa is in the range of 0.95 to 1.04 MPa, and the outlet pressure on the fresh water side is substantially atmospheric pressure, but it is set to 10 kPa or less in consideration of pressure loss that occurs in practice. This value is set because it is a pressure region where energy is generated most efficiently from the amount and pressure of water obtained from the difference in concentration between seawater and fresh water. In addition, the water permeability obtained by using the concentration difference as the driving force is affected by the salt concentration and concentration polarization on the membrane surface. Therefore, the condition that defines the value of the water permeability is twice that of the water permeability. The flow rate that flows to the outside of the membrane and the flow rate that is discharged from the opening at the other end of the hollow fiber type semipermeable membrane was set to 10% of the water permeability in consideration of practical aspects. 10% is in the range of 9.5% to 10.4%. Moreover, since the flow velocity and pressure loss inside the hollow differ depending on the length of the hollow fiber type semipermeable membrane, the length of the hollow fiber type semipermeable membrane when the water permeation amount is defined is defined as about 70 cm. The water permeability is preferably high in order to reduce the required membrane area and increase the throughput, and is preferably 40 L / m ² / day or more, more preferably from the viewpoint of competitiveness with the conventional hollow fiber type or spiral type. 50 L / m ² / day or more, more preferably 60 L / m ² / day or more. Although there is no problem even if the water permeability is too high, the upper limit is 90 L / m ² / day in view of the balance with the separation performance to be achieved. In addition, the water permeability due to the concentration difference generally tends to be higher as the membrane has a higher water permeability due to the pressure difference. This is thought to be because the flow resistance when water permeates inside the membrane is small, but the removal of salt When the performance is not high, or when the concentration polarization on the surface of the membrane having a separation function is large due to the membrane structure with small salt diffusion inside the membrane, the effective concentration difference through the membrane is low, even depending on the pressure Even if the water permeability is high, there are cases where the water permeability due to the concentration difference is low.
In the case of the hollow fiber type semipermeable membrane in the present invention, the leakage of the salt to the low-concentration solution side is a small level, and the concentration difference through the membrane is not lowered due to the leakage of the salt, and can be secured stably. Since the diffusion of salt inside the membrane is ensured and the concentration polarization is expected to be small, the greater the amount of water permeation due to the pressure difference and the smaller the permeation resistance, the greater the amount of water permeation due to the concentration difference.
In addition, when allowing fresh water to permeate using the concentration difference as a driving force, the direction in which fresh water permeates is from the outside to the inside of the hollow fiber type semipermeable membrane and from the inside to the outside of the hollow fiber type semipermeable membrane. There are cases. It can be set as appropriate in consideration of the concentration, characteristics, flow rate level, etc. of the solute of the high concentration solution.

The semipermeable membrane of the present invention is designed so that the maximum performance can be exhibited when used for water treatment with concentration difference as driving force, but water treatment with relatively low pressure difference as driving force. Also has excellent selective permeation performance. The water permeability when an aqueous solution with a sodium chloride concentration of 1.5 g / L is filtered from the outside to the inside of the hollow fiber type semipermeable membrane at 25 ° C. and a pressure of 1.5 MPa is 100 to 300 L / m ² / day. It is possible to express a salt removal rate of 96.0 to 99.9%. The value at the time of filtration at a pressure of 1.5 MPa was defined because the semipermeable membrane of the present invention is intended for use at a low operating pressure. The water permeation amount is preferably high in order to reduce the installation space during water treatment and increase the treatment amount, and is preferably 120 L / m ² / day from the viewpoint of the advantage of compactness over the conventional hollow fiber type and spiral type. As mentioned above, More preferably, it is 140 L / m < ² > / day or more. Although there is no problem if the water permeability is too high, the upper limit is 300 L / m ² / day in view of the balance with the salt removal rate to be achieved. The salt removal rate should be considered from the balance with the water permeability to be achieved, and is 96.0 to 99.9%, preferably 97.0 to 99.5%, and more preferably 98.0 to 99.0. %.

  The semipermeable membrane of the present invention preferably has a dense layer near the outer surface, and the dense layer preferably has a thickness of 0.1 to 7 μm. The dense layer, which is a substantial separation active layer, is preferably as thin as possible because the water permeation resistance is small, preferably 6 μm or less, and more preferably 5 μm or less. However, if the dense layer is too thin, potential defects in the membrane structure are likely to be manifested, and it becomes difficult to suppress the leakage of monovalent ions, or the durability of the membrane may decrease. There is. Therefore, the thickness of the dense layer is more preferably 0.5 μm or more, and further preferably 1 μm or more. In reverse osmosis membranes using a conventional pressure difference as the driving force, the concentration polarization on the membrane surface has a significant effect on the membrane performance. The effect of concentration polarization must be taken into account and improved.

  Since the semipermeable membrane of the present invention allows water to permeate from the low concentration aqueous solution through the membrane to the pressurized high concentration aqueous solution using the concentration difference as a driving force, the pressure resistance as in the conventional high pressure type semipermeable membrane is not Although not required, a certain level of pressure resistance is a characteristic necessary for stable use over a long period of time. In general, a semipermeable membrane made of a polymer causes the membrane to be consolidated in a state under pressure, resulting in a decrease in water permeability. The change with time is generally approximated by a negative exponential function of time, and the rate of change at the beginning of operation is large, but stabilizes with time. Therefore, the rate of change in water permeability performance at the initial stage of operation can be used as an estimation index for long-term performance stability. For example, the water permeability ratio represented by the ratio of the water permeability at the time of 24 hours and the initial water permeability (at the time of 1 hour) can be a performance retention ratio indicating pressure resistance. This is preferably 0.7 or more, more preferably 0.85 or more, and even more preferably 0.9 or more. The pressure resistance evaluation pressure is set to 3 MPa in consideration of actual operating conditions (0.5 to 3 MPa). Under the operating conditions here, in order to rotate the turbine on the high concentration side, it is held in a pressurized state, and this pressure is smaller than the osmotic pressure difference that the concentration difference has, and is usually set to about half of the osmotic pressure. As the salt concentration on the high concentration side, seawater that is widely present is typical, and when including seawater in areas with high salt concentration, it is about 3.5% to 7%, so the osmotic pressure of 3 MPa to 6 MPa is considered. In this case, the maximum value of the pressurizing pressure under the operating conditions is about 3 MPa, and it is practical if pressure resistance and durability of about 3 MPa are ensured.

  The inner diameter of the semipermeable membrane of the present invention is 50 to 200 μm, preferably 65 to 190 μm, more preferably 75 to 160 μm. If the inner diameter is smaller than the above range, the pressure loss of the fluid flowing through the hollow portion is generally increased. Therefore, if the length of the hollow fiber type semipermeable membrane is relatively long, an excessively high pressure is applied when a desired flow rate of fresh water flows. This is not preferable because it causes energy loss. On the other hand, when the inner diameter is larger than the above range, the hollow ratio and the module membrane area are in a trade-off relationship, and it is necessary to sacrifice either the durability at the working pressure or the membrane area per unit volume.

  The outer diameter of the semipermeable membrane of the present invention is 100 to 280 μm, preferably 115 to 270 μm, more preferably 120 to 250 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, which is one of the merits of the hollow fiber type semipermeable membrane module, is impaired.

The hollowness of the semipermeable membrane of the present invention is preferably 24 to 42%, more preferably 25 to 40%, and still more preferably 26 to 38%. When the hollow ratio is smaller than the above range, the membrane resistance increases and the desired water permeability may not be obtained. Moreover, when the hollow ratio is larger than the above range, there is a possibility that sufficient pressure resistance cannot be ensured even when used in low pressure processing.
The hollow ratio (%) can be obtained by the following formula.
Hollow ratio (%) = (inner diameter / outer diameter) ² × 100

  The length of the semipermeable membrane of the present invention is preferably 15 to 500 cm, more preferably 20 to 400 cm, and even more preferably 25 to 300 cm. This length is a range which may be generally used in a hollow fiber type semipermeable membrane module. 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.

  Next, an example of the manufacturing method of the semipermeable membrane of the present invention will be described. As shown in FIG. 1, the semipermeable membrane of the present invention is a hollow fiber type semipermeable membrane produced by discharging a membrane forming stock solution from a spinneret through an aerial running section into a coagulation bath. The membrane is produced by washing the membrane with water and then subjecting it to a hydrothermal treatment to shrink the membrane. The method for producing a semipermeable membrane of the present invention is characterized in that, in order to promote asymmetry of the membrane, the polymer concentration in the membrane forming stock solution is set relatively high and the solvent / non-solvent ratio is set high. To do. When the film-forming stock solution having such characteristics is discharged from a high-temperature nozzle, a larger amount of solvent evaporates in the aerial traveling section, so that polymer aggregation (nucleation) occurs. In the subsequent coagulation bath, since the solvent concentration is set low, the solidification is completed faster than the phase separation proceeds, so that the outer surface structure of the hollow fiber type semipermeable membrane is made thinner and denser. . On the other hand, since the inner surface side (hollow part side) is a closed system and evaporation of the solvent is restricted, polymer nucleation → growth (progress of phase separation) proceeds from the aerial traveling part to the coagulation bath, and asymmetry is thus reduced. Facilitate. The hollow fiber type semipermeable membrane thus obtained is subjected to hydrothermal treatment under a specific range of temperature conditions to cause appropriate membrane shrinkage and densify the outer surface layer. Fix the membrane structure in a slightly loose state.

  As the membrane forming stock solution, a membrane material containing cellulose acetate, a solvent and a non-solvent is used, and if necessary, an organic acid and / or an organic amine is added. Cellulose acetate is preferably cellulose triacetate. 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, they are phthalic acid, tartaric acid, ε-amino-n-caproic acid, benzoic acid, 4-methylaminobutyric acid, p-oxybenzoic acid, and maleic acid, and one or more kinds can be mixed and used. . As the organic amine, any of primary, secondary, and tertiary hydroxyalkylamine can be used. Specifically, monoethanolamine, triethanolamine, diisopropanolamine, and triisopropanolamine are preferable. Triisopropanolamine is particularly preferred.

  The concentration of cellulose acetate in the film-forming stock solution is preferably 40 to 45% by weight. If the concentration of cellulose acetate is lower than the above range, the hollow fiber type semipermeable membrane structure may become too coarse, and sufficient separation performance and membrane strength may not be obtained. There is a possibility that the stability of the film formation cannot be obtained or the water permeability of the obtained film cannot be increased. Moreover, it is preferable that the weight ratio of the solvent / non-solvent in the film-forming stock solution is 80/20 to 95/5. If the solvent / non-solvent weight ratio is lower than the above range, the evaporation of the solvent does not proceed, the membrane surface structure is not densified, and the water permeability does not change greatly, but the separation performance is low. 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., arc type, C type, tube-in-orifice type Extrude from nozzle. When a tube-in-orifice type nozzle is used, it is preferable to use air, nitrogen, carbon dioxide, argon or the like as the hollow forming material. The extruded film-forming stock solution passes through the aerial traveling part (in the gas atmosphere) for 0.02 to 0.4 seconds, and then is immersed in an aqueous coagulation bath to be solidified.

  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. Although 100% water may be used, the amount of waste liquid from the coagulation bath increases in continuous film formation.

  The hollow fiber type semipermeable membrane pulled up from the coagulation bath is washed away with residual solvent, non-solvent and the like with water. As the water washing method, for example, flush water is allowed to flow through a long sloping bowl, and the multi-stage sloping water washing system in which the water is washed through the hollow fiber type semipermeable membrane in the washing water, and the two long rollers have an angle with each other, In the Nelson roller where the hollow fiber type semipermeable membrane is rolled up several times on the roller, the surface of the Nelson roller is always wetted with washing water, and the water is washed by contact with the washing water and the hollow fiber type semipermeable membrane. Further, there are a net shower rinsing method in which the hollow fiber type semipermeable membrane is shaken off on the net and washed with shower water, and an immersion water rinsing method in which the hollow fiber type semipermeable membrane is directly immersed in deep bath rinsing water. In the present invention, water may be washed by any washing method.

  It is preferable that the hollow fiber type semipermeable membrane subjected to the water washing treatment is immersed in water in an unstrained state and subjected to hot water treatment at a temperature higher than 70 ° C. and not higher than 80 ° C. for 5 to 60 minutes. More preferably, the hydrothermal treatment is performed at 72 to 80 ° C., and more preferably at 74 to 80 ° C., thereby fixing the membrane structure, improving the dimensional stability, and improving the thermal stability. For this purpose, the hot water treatment is usually performed at a temperature higher than the glass transition temperature and lower than the melting point. Even when cellulose acetate is used, a hydrothermal treatment temperature of 90 ° C. or higher is generally adopted in a wet state, but in the present invention, a treatment temperature in a specific range of more than 70 ° C. and 80 ° C. or less is adopted. This suppresses excessive densification of the film structure.

  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 hydrothermal treatment 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 type semipermeable membrane of the present invention obtained as described above is incorporated as a hollow fiber type semipermeable membrane module. As an example, there is a method of incorporating a semipermeable membrane by a conventionally known method. For example, as described in Japanese Patent No. 4421486, Japanese Patent No. 4277147, Japanese Patent No. 3591618, Japanese Patent No. 3008886, etc. 45 to 90 thread type semipermeable membranes are collected to form one hollow fiber type semipermeable membrane assembly, and a plurality of hollow fiber type semipermeable membrane assemblies are arranged side by side as a flat hollow fiber type semipermeable membrane bundle. Wrap while traversing around a core tube with many 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 type semipermeable membrane element. The obtained hollow fiber type semipermeable membrane element is inserted into a pressure vessel to assemble a hollow fiber type semipermeable membrane module.

  The module using the hollow fiber type semipermeable membrane of the present invention increases the concentration of a high-concentration aqueous solution in a pressurized state of 0.5 to 3.0 MPa by allowing fresh water to permeate from the low-concentration aqueous solution using a concentration difference as a driving force. It is suitable for an application for generating energy using the pressurized water. Preferred high-concentration aqueous solutions include seawater that is abundant in nature, concentrated seawater, or artificially-obtained high-concentration aqueous solutions. The higher the concentration of the preferred high-concentration aqueous solution, the better, and the osmotic pressure also depends on the molecular weight of the solute. However, it is 0.5 to 10 MPa, preferably 1 to 7 MPa, and more preferably 2 to 6 MPa. According to the module using the hollow fiber type semipermeable membrane of the present invention, the water permeability is high when the membrane has high water permeability and the difference in salt concentration is used as the driving force due to the high separation between water and salt. Therefore, it is possible to efficiently obtain pressurized water using the concentration difference as a driving force.

  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) Inner diameter, outer diameter, and hollow ratio The inner diameter, outer diameter, and film thickness of the hollow fiber type semipermeable membrane are determined by inserting the hollow fiber type semipermeable membrane into a hole of φ3 mm formed in the center of the slide glass. A suitable number of membranes are passed so that the membrane does not fall off, and the hollow fiber type semipermeable membrane is cut with a razor along the upper and lower surfaces of the slide glass to obtain a hollow fiber type semipermeable membrane cross-section sample, and then the projector Nikon PROFILE PROJECTOR V- 12 is used to measure the minor axis and major axis of the cross section of the hollow fiber type semipermeable membrane. For each cross section of the hollow fiber type semipermeable membrane, the minor axis and the long axis are measured in two directions, and the arithmetic average values thereof are taken as the inner diameter and the outer diameter of one cross section of the hollow fiber type semipermeable membrane. (Inner diameter) / 2. The same measurement was performed for the five cross sections, and the average values were taken as the inner diameter, outer diameter, and film thickness.
The hollow ratio was calculated by (inner diameter / outer diameter) ² × 100.

(2) Water permeability due to pressure difference The hollow fiber type semipermeable membrane was bundled and inserted into a plastic sleeve, and then a thermosetting resin was injected into the sleeve, cured and sealed. By cutting the end of a hollow fiber type semipermeable membrane cured with a thermosetting resin, an opening surface of the hollow fiber type semipermeable membrane is obtained, and the membrane area on the basis of the outer diameter is about 0.1 m ² A module 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.
A supply aqueous solution having a sodium chloride concentration of 1.5 g / L is filtered from the outside to the inside of the hollow fiber type semipermeable membrane at 25 ° C. and a pressure of 1.5 MPa, and is operated for 1 hour. Thereafter, the membrane permeated water was collected from the opening surface of the hollow fiber type semipermeable membrane, and the weight of the permeated water was measured with an electronic balance (Shimadzu Corporation LIBROR EB-3200D). The permeated water weight was converted to a permeated water amount of 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] = weight of permeate [L] / outer diameter reference membrane area [m ² ] / collection time [min] × (60 [min] × 24 [hour])
Further, the water permeability is measured in the same manner under the above conditions with the operating pressure of 3.0 MPa, and the ratio with the measured value of the water permeability after 24 hours is calculated from the following formula as the pressure resistance of the membrane.
Permeability ratio [−] = water permeability at 3.0 MPa after 24 hours / water permeability at 3.0 MPa after 1 hour

(3) Salt removal rate due to pressure difference Membrane permeated water collected in the above-mentioned water permeation measurement and a sodium chloride concentration 1.5 g / L aqueous solution used in the same water permeation measurement were measured with an electric conductivity meter (Toa DKK Corporation CM- 25R) is used to measure the sodium chloride concentration.
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

(4) Water permeability due to concentration difference (production of hollow fiber type semipermeable membrane element)
These hollow fiber type semipermeable membranes were arranged in an intersecting manner around a supply fluid distribution pipe made of a porous tube to form an aggregate of hollow fiber type semipermeable membranes. The hollow fiber type semipermeable membrane is arranged in an intersecting manner by traversing the bundle of hollow fiber type semipermeable membranes while rotating the supply fluid distribution tube about its axis, and striking around the supply fluid distribution tube. The hollow fiber type semipermeable membrane in the outermost layer was about 41 degrees with respect to the axial direction. Both ends of this hollow fiber type semipermeable membrane aggregate are fixed by potting with an epoxy resin, then both ends are cut to open the hollow holes of the hollow fiber type semipermeable membrane, and the hollow fiber type semipermeable membrane element Was made. The hollow fiber type semipermeable membrane assembly of this hollow fiber type semipermeable membrane assembly had an outer diameter of 117 mm and an axial length between the open ends of 58 cm. The average effective length of the hollow fiber type semipermeable membrane was about 70 cm. The effective membrane area was about 67 m ² on the basis of the outer diameter of the hollow fiber type semipermeable membrane.
(Measurement of water permeability of module)
This element is loaded into a pressure vessel, and among the nozzles communicating with the respective openings of the hollow fiber type semipermeable membrane, fresh water having a sodium chloride concentration of 0 g / L is supplied from one nozzle by a supply pump, and the other nozzle From which fresh water was allowed to flow. A high-concentration aqueous solution having a sodium chloride concentration of 35 g / L is supplied to a supply fluid distribution pipe communicating with the outside of the hollow fiber type semipermeable membrane by a supply pump, and after passing through the outside of the hollow fiber type semipermeable membrane, the hollow fiber type It flows out from the nozzle which exists in the side surface of the pressure vessel connected to the outside of the semipermeable membrane assembly, and the pressure and the flow rate are adjusted by the flow rate adjusting valve. The supply pressure of the high concentration aqueous solution is PDS1 (MPa), the supply flow rate is QDS1 (L / min), the amount of discharged water of the high concentration aqueous solution is QDS2 (L / min), the supply flow rate of fresh water is QFS1 (L / min), When the outflow flow rate is QFS2 (L / min) and the freshwater outflow pressure is PFS2 (kPa), the water permeability of the module (QDS2-QDS1), the pressure, and the flow rate are set to satisfy the following conditions. The flow rate and pressure were adjusted, and the flow rate increment (QDS2-QDS1) of the high-concentration aqueous solution under the conditions was measured as the module water permeability.
PDS1 = 1.0 MPa
PFS2 = 10 kPa or less QDS1 / (QDS2-QDS1) = 2
QFS2 / (QDS2-QDS1) = 0.1
The water permeability (FR) by concentration is calculated from the following formula.
FR [L / m ² / day] = module water permeability [L / min] / outer diameter reference membrane area [m ² ] × (60 [min] × 24 [hour])

(5) Dense layer thickness After the hollow fiber type semipermeable membrane to be evaluated is washed with water, the solvent is replaced by immersion in an order of 25 ° C. 2-propanol (Nacalai Tesque) and cyclohexane (Nacalai Tesque) for 1 hour each. The hollow fiber type semipermeable membrane after solvent replacement is drained and dried for 24 hours in a vacuum dryer (Yamato Vacuum Drying Oven DP41) having an internal temperature of 50 ° C. and an internal pressure of −40 Pa.
The hollow fiber type semipermeable membrane obtained by drying is embedded in a resin, and a section is cut out using a microtome (REICHERT-NISSEI ULTRACUT) so that the cross section of the hollow fiber type semipermeable membrane can be observed.
The cut section is observed with a differential interference microscope (OPTIPHOT mirror base, reflective differential interference device NR, manufactured by Nikon).
From the obtained microscope image, the dense layer thickness at 10 locations was measured, and the average value thereof was defined as the dense layer thickness.

Example 1
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 49.9 wt%, ethylene glycol (EG, Mitsubishi Chemical) 8.8 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 75 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Example 2)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 44% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 47.3% by weight, ethylene glycol (EG, Mitsubishi Chemical) 8.4% by weight % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 72 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Example 3)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical Corp.) 47.0 wt%, ethylene glycol (EG, Mitsubishi Chemical Corp.) 11.7 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 80 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

Example 4
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 52.8 wt%, ethylene glycol (EG, Mitsubishi Chemical) 5.9 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 72 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Example 5)
In the same manner as in Example 1, a hollow fiber type semipermeable membrane having an inner diameter of 76 μm, an outer diameter of 120 μm, and a hollow ratio of 40% was obtained.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Example 6)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 52.8 wt%, ethylene glycol (EG, Mitsubishi Chemical) 5.9 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 71 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 170 μm, an outer diameter of 270 μm, and a hollow ratio of 40%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Example 7)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 43 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical Corp.) 51.0 wt%, ethylene glycol (EG, Mitsubishi Chemical Corp.) 5.7 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 72 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 158 μm, an outer diameter of 250 μm, and a hollow ratio of 40%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of the present example, and the water permeation performance due to the pressure difference, the salt removal rate, and the water permeation amount ratio were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 1.

(Comparative Example 1)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41 wt%, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 49.9 wt%, ethylene glycol (EG, Mitsubishi Chemical) 8.8 wt% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 40 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 2)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 38% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 52.4% by weight, ethylene glycol (EG, Mitsubishi Chemical) 9.3% % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 60 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 3)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 41.1% by weight, ethylene glycol (EG, Mitsubishi Chemical) 17.6% by weight % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 60 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 4)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 47% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 44.8% by weight, ethylene glycol (EG, Mitsubishi Chemical) 7.9% by weight % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 98 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 5)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 38% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 43.2% by weight, ethylene glycol (EG, Mitsubishi Chemical) 18.5% by weight % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 88 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 6)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 41% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 41.1% by weight, ethylene glycol (EG, Mitsubishi Chemical) 17.6% by weight % And benzoic acid (Nacalai Tesque) 0.3% by weight were uniformly dissolved at 180 ° C. to obtain a film forming stock solution. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 82 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 7)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 43% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 56.7% by weight, benzoic acid (Nacalai Tesque) 0.3% by weight A film-forming stock solution was obtained by uniform dissolution at 180 ° C. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 65 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 158 μm, an outer diameter of 250 μm, and a hollow ratio of 40%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

(Comparative Example 8)
Cellulose triacetate (CTA, Daicel Chemical Industries, LT35) 38% by weight, N-methyl-2-pyrrolidone (NMP, Mitsubishi Chemical) 61.7% by weight, benzoic acid (Nacalai Tesque) 0.3% by weight A film-forming stock solution was obtained by uniform dissolution at 180 ° C. The obtained film-forming stock solution was degassed under reduced pressure, and then discharged from an arc-type (three-division) nozzle into a space cut off from the outside air at 163 ° C. After passing through a space time of 0.03 seconds, NMP / EG / It was immersed in a 12 ° C. coagulation bath consisting of water = 4.25 / 0.75 / 95. Subsequently, the hollow fiber type semipermeable membrane was washed by a multi-stage inclined submerged washing method and shaken off in a wet state. The obtained hollow fiber type semipermeable membrane was immersed in water at 65 ° C. and annealed for 40 minutes.
The obtained hollow fiber type semipermeable membrane had an inner diameter of 100 μm, an outer diameter of 175 μm, and a hollow ratio of 33%.
An evaluation module having a length of about 100 cm was produced using the hollow fiber type semipermeable membrane of this comparative example, and the water permeability, salt removal rate and water permeability ratio by pressure difference were measured. In addition, an element for measuring the amount of water permeation with a concentration difference of about 70 cm in effective length of the hollow fiber type semipermeable membrane was produced, and the amount of water permeation was measured. The evaluation results are summarized in Table 2.

As is clear from the above results, the hollow fiber type semipermeable membranes of Examples 1 to 7 all have high values of water permeability performance with the concentration difference as the driving force. It is possible to efficiently obtain water and pressure for generating energy using as a driving force. On the other hand, in Comparative Example 1, since the hydrothermal treatment temperature is low, the membrane structure is not sufficiently densified and immobilized, and the water permeability by pressurization is high, but the salt removal rate is insufficient, and the concentration In the case of water treatment using the difference as the driving force, the water permeation performance using the concentration difference as the driving force is low because the concentration difference through the semipermeable membrane cannot be sufficiently obtained due to the leaked salt. In Comparative Example 2, since the polymer concentration is low and the hydrothermal treatment temperature is low, the structure as a whole is not sufficiently densified. In this case, since the salt content leaks and the concentration difference through the semipermeable membrane cannot be taken sufficiently, the water permeability performance using the concentration difference as a driving force is low. In Comparative Example 3, the solvent / non-solvent ratio is large, and solvent evaporation in the air travel part is probably not sufficiently promoted. Therefore, the structure of the membrane surface is not densified as expected, and the separation performance is not high. In the case of water treatment using as a driving force, salt leaks and the concentration difference through the semipermeable membrane cannot be taken sufficiently, so the water permeability performance using the concentration difference as the driving force is low. In Comparative Example 4, the polymer concentration in the film-forming stock solution is high, and the hydrothermal treatment temperature is high. Therefore, the water permeability by pressurization is low, and the water permeability performance in the case of water treatment using the concentration difference as the driving force is also low. . Comparative Example 5 has a low polymer concentration in the membrane-forming stock solution, a large solvent / non-solvent ratio, a high hydrothermal treatment temperature, low water permeability due to pressurization, and a high salt removal rate. The water permeability in the case of water treatment using the concentration difference as a driving force is low. Comparative Example 6 has a large solvent / non-solvent ratio in the film-forming stock solution and a high hot water treatment temperature, so that the water permeability by pressurization is low, and the water permeability performance in the case of water treatment using the concentration difference as the driving force is low. The water permeation performance during water treatment using the concentration difference as the driving force is low. Comparative Example 7 is a system having no non-solvent in the film-forming stock solution, and has a low hot water treatment temperature and a high hollowness ratio. Therefore, the water permeability by pressurization is high, and the water treatment uses a concentration difference as a driving force. Although its water permeability is very high, its pressure resistance is very low, and it is not practical when utilizing a concentration difference for a highly concentrated solution in a pressurized state. Comparative Example 8 is a system in which the polymer concentration in the membrane-forming stock solution is low and there is no non-solvent in the membrane-forming stock solution, but since the hydrothermal treatment temperature is low, the water permeation amount due to the pressure difference is high, but the salt removal rate is low. The water permeability in the case of water treatment using the concentration difference as the driving force is low.
As described in these comparative examples, there are cases where the water permeability due to the difference in concentration is low even though the water permeability due to pressure is high. This is because the salt removal performance is not sufficiently high even if the water permeability by pressure is high, the concentration on the low concentration side increased due to salt leakage, and the diffusion of salt in the membrane on the low concentration side is insufficient. It is presumed that the concentration difference through the membrane could not be taken sufficiently because the concentration polarization increased and the concentration on the low concentration side increased.

  The hollow fiber type semipermeable membrane of the present invention is designed so that the water permeability of the membrane is high, and the water permeability with the difference in salt concentration as the driving force is high due to the high selectivity between water and salt. This is extremely useful in the field of generating energy using a concentration difference as a driving force.

Claims (3)

An aqueous solution having a sodium chloride concentration of 35 g / L at 25 ° C. and a pressure of 1.0 MPa was allowed to flow outside the hollow fiber type semipermeable membrane having a length of 70 cm, and fresh water having a sodium chloride concentration of 25 ° C. having a sodium chloride concentration of 0 g / L was hollow fiber type When flowing inside one open end of the semipermeable membrane and discharging from the other open end at 10 kPa or less, it flows from the inside to the outside of the hollow fiber type semipermeable membrane using the concentration difference as a driving force. 2 times the water permeability is a flow rate flowing into the outside, and water permeability of the conditions the flow rate of exhaust from the inside of the hollow fiber type semipermeable membrane is 10% of the translucent water is 30~90L / m ² / The water permeability is 100 to 300 L / m ² when an aqueous solution having a sodium chloride concentration of 1.5 g / L is filtered from the outside to the inside of the hollow fiber type semipermeable membrane at 25 ° C. and a pressure of 1.5 MPa. A hollow fiber type semipermeable membrane that has an outer diameter of 100 to 2 8 is 0Myu m, inner diameter of 50 to 200 [mu] m, wherein the hollow ratio is 24 to 42%, hollow fiber semipermeable membrane for water treatment for the driving force density differences. A membrane-forming stock solution containing a polymer, a solvent, and a non-solvent is prepared, and this is discharged from the spinneret into the coagulation liquid through the aerial running section to produce a hollow fiber type semipermeable membrane. The method for producing a hollow fiber type semipermeable membrane according to claim 1, which is obtained by shrinking the membrane by hot water treatment after washing with water, wherein the polymer concentration in the membrane forming stock solution is 40 to 45 wt%. And that the solvent / non-solvent weight ratio in the membrane forming stock solution is 80/20 to 95/5, the temperature of the hot water treatment is more than 70 ° C. and 80 ° C. or less, and the solvent is N, N -One or more selected from dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N, N-dimethylsulfoxide, and the non-solvent is ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol Wherein the at least one selected from the call. A hollow fiber type semipermeable membrane module comprising the hollow fiber type semipermeable membrane according to claim 1 incorporated therein.