Forward osmosis membrane and forward osmosis membrane module containing the same

Abstract

To provide a practical forward osmosis membrane where physical durability to pressure in a direction to peel a separation function layer from a support membrane is high and performance as the forward osmosis membrane is good.SOLUTION: A forward osmosis membrane is constituted with a support membrane and a separation function layer. The support membrane is provided with at least a porous support and the separation function layer is provided on the porous support. The porous support is provided with a dense layer and a macro void layer in this order from a surface contacting with the separation function layer in a depth direction. The thickness of the dense layer is 1.0-9.5 μm. Macro void exists 0-0.20 piece / μm in a region A having a depth of 0-5.0 μm from a boundary surface between the separation function layer and the porous support and exists 0.04-0.40 piece / μm in a region B having a depth of 5.0-10.0 μm from the boundary surface between the separation function layer and the porous support.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a forward osmosis membrane and a forward osmosis membrane module including the same. [Background technology]

[0002] Among selective separation technologies for liquid mixtures, membrane separation technology is used in a wide range of fields, including seawater desalination, ultrapure water production, wastewater treatment, and the food industry. Well-known membranes used in membrane separation technology include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. However, in recent years, forward osmosis using forward osmosis membranes has been attracting attention. Forward osmosis membranes have at least a separation layer and can achieve high concentrations of concentration that cannot be achieved with reverse osmosis membranes. In the forward osmosis method, when a raw material liquid and a derivation solution with a higher osmotic pressure are brought into contact via a forward osmosis membrane, the osmotic pressure difference generated on both sides of the separation functional layer drives the movement of the solvent (e.g., water) from the raw material liquid to the derivation solution.

[0003] Generally, the separation functional layer is often a thin film. Therefore, to physically support the separation functional layer, a support membrane such as a porous support or nonwoven fabric is used, and a composite semipermeable membrane, which is constructed by combining this support membrane and the separation functional layer, is often used as a forward osmosis membrane. In forward osmosis, solutions are positioned on both sides of the membrane. Therefore, pressure may be generated in a direction that peels the separation layer away from the support membrane. If the physical durability of the composite semipermeable membrane is low, such pressure may cause the separation layer to detach from the support membrane or rupture, impairing the membrane's performance.

[0004] In this context, Patent Document 1 discloses a composite forward osmosis membrane having a support membrane and a separation functional layer, wherein the support membrane contains a polymer having a specific functional group, and the thickness and compressive strength of the support membrane are set within a specific range. It is explained that this composite forward osmosis membrane suppresses delamination between the support membrane and the separation functional layer. Patent Document 2 discloses a composite semipermeable membrane comprising a substrate, a porous support, and a separation functional layer, wherein the porous support has a dense layer on the substrate side, and the thickness of the dense layer and the number of macrovoids present between the substrate and the dense layer are within a specific range. It is explained that this composite semipermeable membrane can maintain its water permeability even when operated under high pressure.

[0005] Patent Document 3 discloses a separation membrane in which a membrane having a separation function is formed on a substrate made of a long-fiber nonwoven fabric. Patent Document 3 explains that by keeping the proportion of macrovoids at the interface between the substrate and the separation membrane within a specific range, it is possible to suppress the separation membrane from the substrate due to pressure fluctuations during use. Patent Document 4 discloses a composite membrane in which a separation functional layer is provided on a polysulfone membrane, wherein the average pore diameter, average porosity, and amount of metaphenylenediamine diffusion of the layer from the surface to a depth of 1 μm are within a specific range. This composite membrane is described as having high salt rejection rate and high water permeability performance while reducing economic burden and the burden on wastewater treatment. Patent Document 5 discloses a separation membrane comprising a support layer containing a polymer with a specific cellulose backbone, and a polymer matrix layer made of polyamide, on a substrate made of polyester nonwoven fabric, and explains that this separation membrane has high strength, high porosity, and high hydrophilicity, while also having excellent desalination properties. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2020 / 059769 [Patent Document 2] Japanese Patent Publication No. 2018-039003 [Patent Document 3] Japanese Patent Publication No. 2019-093366 [Patent Document 4] Japanese Patent Publication No. 2011-194272 [Patent Document 5] Japanese Patent Publication No. 2013-022588 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the composite forward osmosis membrane described in Patent Document 1 does not have sufficient physical durability against peeling of the separation functional layer from the support membrane, nor does it have sufficient membrane performance as a forward osmosis membrane, and there is room for improvement. The composite semipermeable membrane described in Patent Document 2 is a membrane suitable for reverse osmosis, which selectively separates liquid mixtures by applying high pressure with the separation functional layer side as positive. Because the macrovoids in the porous support are less likely to collapse during high-pressure operation, water permeability in reverse osmosis is maintained. The separation membrane described in Patent Document 3 has improved peel strength between the nonwoven fabric substrate and the porous support made of a polymer. The composite membrane described in Patent Document 4 has improved performance as a reverse osmosis membrane without the need to add new chemicals after the membrane is manufactured. Furthermore, Patent Documents 2-5 do not examine the physical durability of the disclosed membranes against delamination between the support membrane and the separation functional layer. Also, Patent Documents 2-4 do not verify the practical applicability of these membranes as forward osmosis membranes.

[0008] The object of the present invention is to provide a practical forward osmosis membrane and a forward osmosis membrane module containing the same, which have high physical durability against pressure in the direction of peeling the separation functional layer from the support membrane and good performance as a forward osmosis membrane. [Means for solving the problem]

[0009] An example of an embodiment of the present invention for achieving the above objective is shown below. <Aspect 1> A forward osmosis membrane composed of a support membrane and a separation functional layer, The support film comprises at least a porous support, The separation functional layer is provided on the porous support, The porous support comprises a dense layer and a macrovoid layer in this order in the depth direction from the surface in contact with the separation functional layer. The macrovoid layer is a layer having macrovoids with a major axis length of 1.0 μm or more, The dense layer is a layer having no macrovoids, The thickness of the dense layer is 1.0 to 9.5 μm, The macrovoids are present at 0 to 0.20 pieces / μm in a region A from the interface between the separation functional layer and the porous support to a depth of 0 to 5.0 μm, and present at 0.04 to 0.40 pieces / μm in a region B from the interface between the separation functional layer and the porous support to a depth of 5.0 to 10.0 μm, Forward osmosis membrane. <<Aspect 2>> The forward osmosis membrane according to Aspect 1, wherein the macrovoids are present at 0 to 0.16 pieces / μm in the region A. <<Aspect 3>> The forward osmosis membrane according to Aspect 1 or 2, wherein the macrovoids are present at 0.06 to 0.30 pieces / μm in the region B. <<Aspect 4>> The forward osmosis membrane according to any one of Aspects 1 to 3, wherein the macrovoids are present at 0 to 0.12 pieces / μm in the region A. <<Aspect 5>> The forward osmosis membrane according to any one of Aspects 1 to 4, wherein the macrovoids are present at 0.08 to 0.20 pieces / μm in the region B. <<Aspect 6>> The forward osmosis membrane according to any one of Aspects 1 to 5, wherein the number of macrovoids present in the region B is not less than the number of macrovoids present in the region A. <<Aspect 7>> The forward osmosis membrane according to any one of Aspects 1 to 6, wherein the support membrane of the forward osmosis membrane consists only of the porous support. <<Aspect 8>> The forward osmosis membrane according to any one of Aspects 1 to 7, wherein the thickness of the dense layer is 8.0 μm or less. <<Aspect 9>> The forward osmosis membrane according to any one of Aspects 1 to 8, wherein the thickness of the dense layer is 1.5 to 6.0 μm. <<Aspect 10>> The forward osmosis membrane according to any one of Aspects 1 to 9, wherein the support membrane is a hollow fiber support membrane. <<Aspect 11>> The forward osmosis membrane according to Aspect 10, wherein the hollow fiber support membrane has the dense layer at least on the inner surface of the hollow fiber. <Aspect 12> A forward osmosis membrane according to any one of aspects 1 to 11, wherein the coefficient of variation of the average thickness of the separation functional layer in the forward osmosis membrane is 60% or less. <Aspect 13> A forward osmosis membrane according to any one of aspects 1 to 12, wherein the coefficient of variation of the average thickness of the separation functional layer in the forward osmosis membrane is 30% or less. <Aspect 14> A forward osmosis membrane according to any one of aspects 1 to 13, wherein the porous support comprises one or more selected from polysulfone, polyethersulfone, and derivatives thereof. <Aspect 15> A forward osmosis membrane according to any one of aspects 1 to 14, wherein the porous support contains polysulfone. Appearance 16: A forward osmosis membrane module comprising a housing containing a forward osmosis membrane as described in any one of Appearances 1 to 15. <Aspect 17> A hollow fiber membrane comprising at least a porous support, The porous support comprises a dense layer and a macrovoid layer in this order, extending from the outer surface or inner surface in the thickness direction of the membrane wall. The macrovoid layer is a layer having macrovoids whose major axis is 1.0 μm or more. The dense layer is a layer that does not have the macrovoids. The thickness of the dense layer is 1.0 to 9.5 μm. The aforementioned macrovoid is The porous support has 0 to 0.20 particles / μm present in region A from the outer or inner surface to a depth of 0 to 5.0 μm, and 0.04 to 0.40 particles / μm are present in region B of the porous support, from the outer surface or inner surface to a depth of 5.0 to 10.0 μm. Hollow fiber membrane. <Aspect 18> The hollow fiber membrane according to aspect 17, wherein the macrovoids are present in region A at a density of 0 to 0.16 per μm. <Aspect 19> The hollow fiber membrane according to aspect 17 or 18, wherein the macrovoids are present in the region B at a rate of 0.06 to 0.30 per μm. <Aspect 20> The hollow fiber membrane according to any one of aspects 17 to 19, wherein the macrovoids are present in region A at a density of 0 to 0.12 per μm. [Aspect 21] The hollow fiber membrane according to any one of aspects 17 to 20, wherein the number of macrovoids in region B is equal to or greater than the number of macrovoids in region A. [Aspect 22] The hollow fiber membrane according to any one of aspects 17 to 21, wherein the hollow fiber membrane consists only of the porous support. [Aspect 23] A hollow fiber membrane according to any one of aspects 17 to 22, wherein the thickness of the dense layer is 8.0 μm or less. [Aspect 24] A hollow fiber membrane according to any one of aspects 17 to 23, wherein the thickness of the dense layer is 1.5 to 6.0 μm. <Aspect 25> The hollow fiber membrane according to any one of aspects 17 to 24, wherein the hollow fiber membrane has the dense layer on at least the inner surface of the hollow fiber. [Aspect 26] The hollow fiber membrane according to any one of aspects 17 to 25, wherein the porous support comprises one or more selected from polysulfone, polyethersulfone, and derivatives thereof. [Aspect 27] The hollow fiber membrane according to any one of aspects 17 to 26, wherein the porous support contains polysulfone. [Aspect 28] The hollow fiber membrane according to any one of aspects 17 to 27, wherein the hollow fiber membrane is used as a support membrane for a forward osmosis membrane. [Aspect 29] A hollow fiber membrane module comprising a housing containing a hollow fiber membrane as described in any one of aspects 17 to 28. <Aspect 30> Discharge a spinning stock solution containing resin and solvent from the outer channel of the double-tubular nozzle, and discharge an internal solidifying liquid from the inner channel of the double-tubular nozzle; The spinning liquid discharged from the outer channel of the double-tubular nozzle is immersed in the external coagulation solution via the air-flow portion to coagulate it; and Applying tension to the solidified spinning solution while winding the spinning solution onto the winding solution. Includes, The aforementioned spinning solution comprises a resin (polymer) and a solvent. The temperature of the spinning solution discharged from the double-tubular nozzle is higher than the temperature of the internal coagulation solution, and the temperature difference between the two solutions is 5°C or more and less than 35°C. A method for manufacturing hollow fiber membranes. <Aspect 31> The manufacturing method according to aspect 30, wherein the tension is 4g or more and 60g or less. <Aspect 32> The manufacturing method according to aspect 30 or 31, wherein the temperature of the free-running portion is 15°C or more and 50°C or less. [Aspect 33] The manufacturing method according to any one of aspects 30 to 32, wherein the relative humidity of the air-running portion is 40% or more and 100% or less. [Effects of the Invention]

[0010] A forward osmosis membrane according to one aspect of the present invention may possess both physical durability in the direction of peeling the separation functional layer from the support membrane and good performance as a forward osmosis membrane. A hollow fiber membrane according to another aspect of the present invention can not only be suitably used as a support membrane for a forward osmosis membrane, but can also be a separation membrane that exhibits a certain level of water permeability and pressure resistance on its own. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of one embodiment of a hollow fiber membrane module. [Figure 2] This is a scanning electron microscope image of a cross-section of the forward osmosis membrane obtained in Example 1. [Figure 3] Figure 2 is a reference diagram with auxiliary lines added for analysis. [Figure 4] This is a scanning electron microscope image of a cross-section of the forward osmosis membrane obtained in Comparative Example 1. [Figure 5] Figure 4 is a reference diagram with auxiliary lines added for analysis. [Modes for carrying out the invention]

[0012] An example of this embodiment will be described in detail below. 《Forward osmosis membrane》 The forward osmosis membrane of this embodiment is A forward osmosis membrane composed of a support membrane and a separation functional layer, The support film comprises at least a porous support, The separation functional layer is provided on the porous support, The porous support comprises a dense layer and a macrovoid layer in this order in the depth direction from the surface in contact with the separation functional layer. The macrovoid layer is a layer having macrovoids whose major axis is 1.0 μm or more. The dense layer is a layer that does not have the macrovoids. The thickness of the dense layer is 1.0 to 9.5 μm. The aforementioned macrovoid is In region A, from the interface between the separation functional layer and the porous support to a depth of 0 to 5.0 μm, there are 0 to 0.20 particles / μm present, and In region B, from the interface between the separation functional layer and the porous support to a depth of 5.0 to 10.0 μm, there are 0.04 to 0.40 particles / μm present. It is a forward osmosis membrane.

[0013] <Support membrane> The support membrane in the forward osmosis membrane of this embodiment comprises at least a porous support. In addition to the porous support, this support membrane may further comprise a substrate.

[0014] [Base material] The substrate plays a role in providing strength to the support film and, consequently, the forward osmosis film. The substrate is preferably porous to allow solvents to pass through. The substrate is composed of, for example, woven fabric, nonwoven fabric, mesh net, or foamed sintered sheet. Examples of substrate materials include polymers, specifically polyester, polyamide, polyolefin, and mixtures and copolymers thereof. The substrate is preferably a porous material with a larger pore diameter than the porous support and separation functional layer. The thickness of the substrate is preferably in the range of 40 to 150 μm, balancing the need to ensure the strength of the support membrane with the need to maintain the water permeability of the resulting forward osmosis membrane. The substrate is generally a porous material with a larger pore size than the porous support and separation functional layer. The average pore size of the substrate is generally 0.1 to 100 μm. More specifically, it is evaluated by basis weight and air permeability. The basis weight of the substrate is 20 to 150 g / m².2 The air permeability measured by the Frazier method for the substrate is 0.5 to 30 cc / cm³. 2 It is ×sec).

[0015] In this embodiment, it is preferable that the support membrane does not have a substrate, and the forward osmosis membrane consists substantially only of a porous support and a separation functional layer. A support membrane without a substrate has high diffusivity of the induction solution within the support membrane, and can achieve both high water permeability and low salt back diffusion. Here, the phrase "consisting substantially only of a porous support and a separation functional layer" of a forward osmosis membrane means that the components of the forward osmosis membrane are not limited to strictly consisting only of a porous support and a separation functional layer, but may also include optional components such as dispersants, hydrophilic agents, coating agents, humectants, and preservatives for the separation membrane. These optional components may be inorganic compounds or organic compounds.

[0016] [Porous support] The porous support plays a role in providing strength to the separation functional layer. The porous support may have separation capabilities for solvent-insoluble particles, but it is preferable that it substantially does not have separation capabilities for ions dissolved in the solvent. The statement that the porous support substantially does not have separation capabilities means that the separation capabilities of ions, etc., when the porous support is used as a forward osmosis membrane are lower than the separation capabilities of the separation functional layer when it is used as a forward osmosis membrane. In this embodiment, the porous support comprises a dense layer and a macrovoid layer in the thickness direction of the membrane wall from the surface in this order.

[0017] (Dense layer) The dense layer is thought to assist in the formation of a uniform separation functional layer on a porous support, and also to maintain the water permeability within an appropriate range when it is formed as a forward osmosis membrane. In the forward osmosis membrane of this embodiment, the separation functional layer is formed, as described later, for example, by interfacial polymerization of a polyfunctional amine and a polyfunctional acid halide. The dense layer retains and releases the polyfunctional amine solution supplied when forming the separation functional layer. In this way, it plays a role in supplying the polyfunctional amine solution to the polymerization site of the polyamide (the interface between the polyfunctional amine solution and the polyfunctional acid halide solution), and also acts as the starting point for fold growth in the separation functional layer. Furthermore, because the separation functional layer is formed by filling in the fine irregularities of the dense layer, the adhesion between the separation functional layer and the support membrane is enhanced, and when pressure is applied to the separation functional layer in the direction of peeling from the support membrane, that pressure is evenly distributed and relieved. When the dense layer is uniform, advantageous effects such as the ability to maintain water permeability and high adhesion between the separation layer and the support membrane are expressed not only in a part of the membrane but throughout the entire membrane, which is preferable. Furthermore, when the dense layer is uniformly formed, when the forward osmosis membrane of this embodiment is used as a module, the above advantageous effects are expressed throughout the entire module, which is also preferable. A uniform dense layer means that parameters such as thickness and pore size are within a predetermined range, regardless of the location within the dense layer. Furthermore, a uniform dense layer within a module means that the above parameters are within a predetermined range regardless of which part of the forward osmosis membrane within the module is observed.

[0018] To efficiently retain and release the polyfunctional amine solution, it is preferable that the dense layer has continuous pores. A dense layer is a layer that does not contain macrovoids, which will be discussed later. As described later, macrovoids are pores with a major axis of 1.0 μm or larger. Therefore, a dense layer refers to a layer that does not contain pores, or, if it contains pores, a layer in which the major axis of the contained pores is less than 1.0 μm. Preferably, the major axis of the pores contained in the dense layer is 0.5 μm or less. The dense layer preferably contains pores with a major axis of less than 1.0 μm. It is preferable that the major axis of the pores in the dense layer be 0.001 μm or larger, as this allows them to effectively perform the above-mentioned roles. The thickness of the dense layer is 1.0 to 9.5 μm, preferably 1.5 to 9.0 μm, more preferably 2.0 to 8.0 μm, even more preferably 2.5 to 7.5 μm, particularly preferably 3.0 to 7.0 μm, and especially preferably 3.5 to 6.0 μm. Having the above-mentioned thickness of the dense layer is preferable because it can perform the above-mentioned role and ensure water permeability without significantly hindering the permeation of the solvent.

[0019] The dense layer is preferably located on the outermost surface of the porous support. When the dense layer is located on the outermost surface of the porous support, it facilitates the formation of the separation function layer and reduces its defects, and even when the porous support alone is used as a separation membrane, it is possible to maintain a high level of separation function while preventing contamination inside the membrane. When the porous support is in the form of hollow fibers, it is preferable that the dense layer is present on at least the inner surface of the hollow fibers of the porous support. In this embodiment, there may be multiple dense layers. When the porous support has multiple dense layers, it is preferable that the dense layers are located on the outermost surfaces of both sides of the porous support, for example.

[0020] In this embodiment, the dense layer in the support film is the layer in contact with the separation function layer. However, it is conceivable that macrovoids may accidentally reach the surface of the porous support and come into contact with the separation function layer during the fabrication of the porous support constituting the support film. In this case, the layer in contact with the separation function layer may be a macrovoid layer. However, in order to more advantageously demonstrate the effects of this embodiment, it is preferable that the dense layer is present on most of the surface of the porous support that is in contact with the separation function layer. This requirement can be confirmed by observing the cross-section of the porous support under the conditions described later, where the number of cross-sectional images in which macrovoids have reached the surface of the porous support is 50% or less of the total number of cross-sectional images observed. This percentage is most preferably 0%. In this case, when macrovoids accidentally reach the surface of the support film, the term "interface between the separation function layer and the dense layer" in this specification can be interpreted and applied in a broader sense as "interface between the separation function layer and the support film."

[0021] (Macrovoid layer) A macrovoid layer is a layer containing voids (macrovoids) with a major axis of 1.0 μm or more. The thickness of the macrovoid layer is preferably 5 to 300 μm. The macrovoid layer may reach the opposite surface of the porous support, or, if another dense layer exists on the opposite surface of the porous support, it may extend to that dense layer. The size and shape of the macrovoid are not particularly limited, as long as it has a major axis of 1.0 μm or more. However, from the viewpoint of achieving both improved water permeability inside the porous support membrane and durability against applied pressure (pressure resistance), the major axis of the macrovoid is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 120 μm or less, and may also be 100 μm or less or 80 μm or less. From a similar viewpoint, the minor axis of the macrovoid is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, particularly preferably 20 μm or less, and may also be 10 μm or less. The macrovoid layer contains macrovoids with a major axis of 1.0 μm or more, and it is preferable that the average value of the major axis and the average value of the minor axis calculated for all macrovoids contained in the macrovoid layer are within the above range, and it is more preferable that the major axis and minor axis of all macrovoids contained in the macrovoid layer are within the above range. If the major or minor axis of the macrovoid is larger than the range described above, the pressure resistance of the porous support membrane may be impaired, or the porous support membrane may deform during use, resulting in a loss of the intended performance. Furthermore, according to the inventors' studies, macrovoids often have a roughly elliptical cross-section. Also, the major axis direction of a macrovoid is often roughly perpendicular to the interface direction with the dense layer within the macrovoid layer. When the cross-section of a macrovoid is roughly elliptical, the major axis refers to the length of the major axis of the ellipse, and the minor axis refers to the length of the minor axis of the ellipse.

[0022] (Region A and Region B, and the number of macrovoids in these regions) In the forward osmosis membrane of this embodiment, the range from 0 to 5.0 μm in depth from the interface between the separation functional layer and the dense layer (the interface between the separation functional layer and the support membrane) is defined as "Region A," and the range from 5.0 to 10.0 μm in depth from the interface between the separation functional layer and the dense layer (the interface between the separation functional layer and the support membrane) is defined as "Region B." Here, macrovoids with a major axis of 1.0 μm or more are present in region A at a rate of 0 to 0.20 voids / μm in the planar direction (a direction parallel to the film plane direction, as shown in Figure 2). The number of macrovoids in region A is preferably 0 to 0.16 voids / μm, more preferably 0 to 0.12 voids / μm, and even more preferably 0.02 to 0.10 voids / μm. Furthermore, the number of macrovoids in region B is 0.04 to 0.40 per μm in the planar direction. Preferably, the number of macrovoids in region B is 0.06 to 0.30 per μm, more preferably 0.08 to 0.20 per μm, and even more preferably 0.10 to 0.19 per μm. The number of macrovoids in region B is preferably equal to or greater than the number of macrovoids in region A, and more preferably greater than the number of macrovoids in region A.

[0023] In this embodiment, the adhesion between the separation functional layer and the support film is enhanced when the number of macrovoids in regions A and B satisfies these specific numerical ranges. Furthermore, when pressure (reverse pressure) is applied in the direction that peels the separation functional layer away from the support film, it becomes possible to evenly distribute and relieve that pressure, resulting in high durability. This is preferable because it expands the degree of freedom in equipment design, operating conditions, etc., when used as a forward osmosis membrane. Furthermore, a support membrane in region B where the number of macrovoids falls within the specified numerical range maintains physical durability while preserving the diffusivity of the induction solution within the support membrane when used as a forward osmosis membrane. This improves the water permeability of the forward osmosis membrane, resulting in highly efficient solution processing. Furthermore, if regions A and B of the porous support each have the specific number of macrovoids described above, the porous support may be used as a separation membrane. In this case, by satisfying the macrovoid number requirement in region A, both improved membrane separation performance and reduced contamination inside the membrane can be achieved. Also, by satisfying the macrovoid number requirement in region B, both high water permeability and high strength can be achieved.

[0024] (Measurement of the thickness of the dense layer and the number of macrovoids in regions A and B) Whether a porous support satisfies the above conditions can be checked as follows. The support membrane or forward osmosis membrane is cut perpendicular to the membrane plane at any point to obtain a cross-section. This cross-section is observed under a microscope to obtain a cross-sectional image with a width of at least 5 μm. Voids (macrovoids) with a major axis of 1.0 μm or larger are searched for in this cross-sectional image. If a macrovoid with a major axis of 1.0 μm or larger is present in the cross-sectional image, the shortest distance between the outer edge of that macrovoid (the apex) closest to the separation functional layer and the separation functional layer is measured, and this distance is defined as the thickness of the dense layer. If multiple voids are present in the cross-sectional image, the void whose apex is closest to the separation functional layer is selected, and the distance between the apex of that void and the separation functional layer is measured, and this distance is defined as the thickness of the dense layer. If no voids with a major axis of 1.0 μm or larger are found in the cross-sectional image, the observation magnification is reduced and the microscopic observation is repeated in a wider field of view. If no voids with a major axis of 1.0 μm or larger are found even then, up to 50 images are acquired from different locations, and the 9 images with the highest number of macrovoids in region B are used, with the average value calculated.

[0025] The depth range from 0 to 5.0 μm from the interface between the separation functional layer and the dense layer is defined as "Region A," and the depth range from 5.0 to 10.0 μm from the interface between the separation functional layer and the dense layer is defined as "Region B." In these Regions A and B, the number of macrovoids with a major axis of 1.0 μm or more is counted, and the number is divided by the width of the cross-section of the observed film to calculate the number of macrovoids in each Region A and Region B.

[0026] The thickness of the dense layer and the number of macrovoids in regions A and B are measured using n=9, and the average value is taken as the measurement value. That is, nine film samples are prepared, the above procedure is performed on each sample, and the values ​​are calculated as the average value. The sampling locations for the nine samples may be set as appropriate, in accordance with the measurement of the coefficient of variation of the average thickness of the separation functional layer described later. For each membrane sample, by observing the vicinity of the interface where the porous support and the separation functional layer in the support membrane are in contact, or the vicinity of the surface of the support membrane, using a scanning electron microscope or a transmission electron microscope, the thickness of the dense layer of the porous support in the support membrane, as well as the number of macrovoids in regions A and B, can be measured.

[0027] The following describes examples of observations performed using a scanning electron microscope. For cross-sectional images obtained with a scanning electron microscope, the sample can be prepared and observed, for example, as follows: The film sample is immersed in pure water and frozen using liquid nitrogen, then dried by freeze-drying. After drying, the sample is cut or prepared by the Broad Ion Beam (BIB) method, preferably the BIB method, to create a cross section perpendicular to the film surface direction. The obtained cross section is thinly coated with platinum, platinum / palladium, osmium tetroxide, or osmium, preferably osmium, to be used as the observation sample. The cross section of this observation sample is observed at an accelerating voltage of 1 to 6 kV, preferably 1 kV. The observation magnification should be such that the contact interface between the porous support and the separation functional layer, or the area near the surface of the support film, can be observed. For example, 1,000 to 20,000 times is preferred, and 5,000 times is more preferred.

[0028] From the obtained electron microscope images (cross-sectional images), the thickness of the dense layer, the size of the voids, etc., can be directly measured using a scale, and the respective values ​​can be calculated using the procedure described above. Each measurement can be obtained as an average value within a measurement range of approximately 5 to 100 μm in cross-sectional width. This measurement range is preferably 10 to 50 μm, more preferably 20 to 30 μm, and most preferably 25 μm.

[0029] In this embodiment, the contact interface between the porous support of the forward osmosis membrane and the separation functional layer can be specifically confirmed, for example, as follows. One method involves capturing images of a cross-section of a forward osmosis membrane using a scanning electron microscope, importing these images into appropriate image processing software, and processing them. An example of such image processing software is ImageJ (developed by the National Institutes of Health, USA). The SEM images imported into ImageJ are binarized using a known binarization method, preferably the Otsu method, which is appropriately selected based on the obtained images. For the entire resulting binarized image, the average brightness in the direction horizontal to the membrane surface is calculated at predetermined distances (e.g., 1 pixel) in the depth direction from the membrane surface. The average brightness is then compared from the surface of the separation functional layer toward the support membrane, and the horizontal direction of the portion with the highest average brightness can be identified as the contact interface between the porous support of the forward osmosis membrane and the separation functional layer. It is preferable to observe the forward osmosis membrane so that the surface of the separation functional layer is as horizontal as possible within the field of view. The observation magnification of the cross-sectional image is preferably 1,000 to 20,000 times, and more preferably 5,000 times. The width of the cross-section (length in the direction parallel to the interface between the support membrane and the separation functional layer) can be 5 to 100 μm, preferably 10 to 50 μm, more preferably 20 to 30 μm, and most preferably 25 μm. Furthermore, even if the contact interface between the porous support and the separation functional layer of the forward osmosis membrane is wavy, the contact interface between the porous support and the separation functional layer of the forward osmosis membrane can be uniquely identified by the method described above, unless the forward osmosis membrane is intentionally bent for observation.

[0030] (Material for porous support) The material of the porous support is not particularly limited. However, from the standpoint of ease of molding, the porous support is preferably made of a resin, and more preferably made of a thermoplastic resin. Here, a thermoplastic resin refers to a material made of chain polymers that exhibits the property of deforming or flowing when heated by an external force. Examples of thermoplastic resins include polysulfone, polyethersulfone, polyketone, polyamide, polyester, cellulosulfone, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide. These homopolymers or copolymers can be used individually or in blends of two or more. Furthermore, derivatives of these polymers having any functional group in the main chain, side chain, or terminal can also be used as resins constituting porous supports.

[0031] Here, as cellulosic polymers, cellulose acetate, cellulose nitrate, etc., can be used; as vinyl polymers, polyethylene, polypropylene, polyvinyl chloride, chlorinated vinyl chloride, polyacrylonitrile, etc., can be used. Among these, one or more selected from polysulfone, polyacrylonitrile, polyamide, polyester, polyvinyl alcohol, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene sulfide, polyethersulfone, polyvinylidene fluoride, cellulose acetate, polyvinyl chloride, and chlorinated vinyl chloride are preferred. More preferably, cellulose acetate, polysulfone, polyethersulfone, polyketone, and polyacrylonitrile are used. Among these materials, polysulfone or polyethersulfone is preferred because it has high chemical, mechanical, and thermal stability and is easy to mold. The porous support preferably contains the resins listed above or their derivatives as its main component. Here, "main component" means that it is present in an amount of 50% by mass or more of the total mass of the porous support. Polysulfone is even more preferred as the material for the porous support due to its ease of pore size control.

[0032] (Thickness and shape of the porous support) When the support film consists of a composite structure of a substrate and a porous support, the thickness of the porous support is preferably 0.02 to 0.10 mm from the viewpoint of balancing water permeability resistance and strength. On the other hand, when the support membrane consists only of a porous support, from the viewpoint of balancing water permeability resistance and strength, the thickness of the porous support is preferably 0.05 to 3.00 mm, more preferably 0.10 to 1.00 mm, and even more preferably 0.15 to 0.50 mm. When the support membrane consists solely of a porous support, the porous support is preferably in the form of a film (flat film), a tube, or a hollow fiber, and may also be a shape obtained by chemically or physically deforming these. The porous support is more preferably hollow fiber in order to accommodate a larger membrane area in a smaller space. Here, "hollow fiber" means the shape of a hollow tube with an outer diameter of approximately 5 mm or less, and "tubular" means the shape of a hollow tube with an outer diameter of approximately more than 5 mm.

[0033] [Physical properties of the support film] The physical properties of the support membrane can be indicated by the amount of pure water permeability, compressive strength, etc. Some of these physical properties can be measured in the state of a support membrane module, in which one or more support membranes are housed within a housing; they can be measured in the state of the support membrane after disassembling the support membrane module and removing it; and they can be measured after removing the separation functional layer of the forward osmosis membrane using known methods, to the extent that the properties of the support membrane are not significantly impaired. The physical properties are measured by the method described in the examples below.

[0034] [Pure water permeability] In order to achieve both water permeability resistance and membrane strength, and to facilitate the formation of a suitable separation functional layer, the pure water permeability of the hollow fiber-supported membrane is preferably 10 to 1000 kg / m³. 2 (×hr × bar)) and more preferably 50~700 (kg / (m 2(×hr × bar)) and more preferably 100 to 700 (kg / (m 2 (×hr × bar)) and particularly preferably 300~600 (kg / (m 2 It is ×hr × bar). [Compressive strength] From the viewpoint of providing the support membrane with practical strength and achieving both water permeability resistance and strength, the compressive strength of the hollow fiber support membrane is preferably 0.25 to 1.5 MPa, more preferably 0.40 to 1.2 MPa, and even more preferably 0.50 to 1.0 MPa. By ensuring the support membrane has a compressive strength within the above range, the performance of the forward osmosis membrane can be maintained more reliably. When the compressive strength is too high, the cross-sectional structure of the membrane is often excessively dense, leading to increased water permeability resistance and internal concentration polarization. In this case, the water permeability of the forward osmosis membrane tends to decrease. To increase the compressive strength of the support film, it is effective to increase the polymer concentration and increase the thickness of the support film during the deposition of the porous support.

[0035] [Inner diameter and outer shape of hollow fiber support membrane] When the support membrane is a hollow fiber support membrane, the inner diameter and outer shape of the hollow fiber support membrane are not particularly limited. However, considering film formation stability, ease of handling, and membrane area when formed into a module, an outer diameter of 0.10 to 3.00 mm and an inner diameter of 0.03 to 2.50 mm is preferred, an outer diameter of 0.20 to 1.50 mm and an inner diameter of 0.10 to 1.00 mm is more preferred, and considering the balance between allowing raw material liquid containing poorly soluble substances to pass through the hollow portion without hindrance and strength, an outer diameter of 0.50 to 1.35 mm and an inner diameter of 0.25 to 1.00 mm is preferred. The thickness of the hollow fiber support membrane is preferably 0.02 to 1.00 mm from the viewpoint of strength, more preferably 0.05 to 0.50 mm from the viewpoint of balancing strength and handling, and further preferably 0.10 to 0.35 mm from the viewpoint of balancing water permeability resistance and strength, and from the viewpoint of the diffusibility of the solution in the film thickness portion (membrane wall portion) when used as a forward osmosis membrane.

[0036] [Separation functional layer] The separation layer in a forward osmosis membrane is primarily responsible for solute separation. More specifically, it separates the solvent in a liquid mixture from the solutes, such as ions, dissolved in that solvent. The composition and thickness of the separation layer are determined according to the intended use of the forward osmosis membrane. The separation functional layer is positioned on the surface of the support film. If the support film has a front and back side, it is preferable to position the separation functional layer on either the front or back side. However, the separation functional layer may also be positioned on both sides of the support film or inside the pores of the support film. The separation functional layer may be present on one side of the support film or on both sides. Furthermore, if the separation functional layer is present on both sides of the support film, the thickness, separation performance, salt inhibition performance, etc., of each side may be the same or different.

[0037] When separation functional layers are arranged on both sides of the support membrane, the "separation functional layer side" in this disclosure refers to the side of the entire forward osmosis membrane that blocks the solute with a higher rejection rate. For example, the following methods can be used to determine which side blocks the solute with a higher rejection rate. The amount of salt backdiffusion into the raw material is evaluated when purified water is placed on one side as the raw material and the induction solution on the other side via a forward osmosis membrane, and when the arrangement of these solutions is reversed. When comparing these two evaluation results, the raw material side with the arrangement that shows less salt backdiffusion can be designated as the side that more efficiently blocks the solute of the induction solution (the separation function layer side). Here, a 3.5% by mass aqueous solution of sodium chloride or a 50% by mass aqueous solution of isopropanol can be used as the induction solution, and preferably a 3.5% by mass aqueous solution of sodium chloride is used.

[0038] Examples of materials for the separation functional layer include one or more selected from high-molecular polymers, inorganic substances, organic-inorganic hybrid compounds, and compositions in which a predetermined inorganic or organic compound is dispersed or compatible with these materials. A separation functional layer composed of a polymer preferentially allows solvent permeability while blocking solutes, thereby possessing substantial separation performance. Suitable polymers for such a separation functional layer include, for example, polyamides, polyvinyl alcohols, sulfonated polyethersulfones, polypiperazineamides, polyimides, and composite materials composed of two or more of these.

[0039] [Polyamide separation functional layer] In this embodiment, a polyamide-based poramide separation functional layer is preferably used from the viewpoint of easily forming a defect-free thin film on a porous support. Here, "primarily composed of polyamide" means a separation functional layer in which the mass ratio of polyamide to the total mass of the separation functional layer is 50% by mass or more, 75% by mass or more, or 95% by mass or more. The mass ratio of polyamide to the total mass of the separation functional layer may be 100% by mass. The polyamide separation functional layer is preferably a polycondensation product of a polyfunctional amine and a polyfunctional acid halide. The formation of the polyamide separation functional layer involves forming a polyamide skeleton by performing interfacial polycondensation on the surface of a porous support using an aqueous solution containing a polyfunctional amine and an organic solvent solution containing a polyfunctional acid halide. The organic solvent in the organic solvent solution containing the polyfunctional acid halide is preferably an organic solvent that is immiscible with water. The method for forming the polyamide separation functional layer will be described in detail later.

[0040] [Average thickness of the separation layer] The average thickness of the separation functional layer is preferable as long as there are no pinholes. However, it is desirable to have an appropriate thickness in order to maintain mechanical strength and chemical resistance. Considering film formation stability, water permeability resistance, etc., for example, the average thickness of the separation functional layer (polymer thin film) made of a polymer is preferably 0.01 to 3 μm, and more preferably 0.05 to 1 μm.

[0041] The average thickness of the separation functional layer is measured by microscopic observation. Specifically, for example, the separation membrane is embedded in resin, then cut to prepare ultrathin sections. The obtained sections are treated with staining or other processes and observed using a transmission electron microscope (TEM) or scanning electron microscope (SEM). A preferred method for measuring film thickness is to take images of the cross-section of the separation functional layer in the thickness direction using a scanning electron microscope, import the images into appropriate image processing software, and process the images. An example of image processing software is ImageJ (developed by the National Institutes of Health, USA). The contour of the separation functional layer is extracted from the SEM image imported into ImageJ, the interior is filled in to calculate the area of ​​the separation functional layer, and this can be converted to the average thickness of the separation functional layer in one image using a pre-created calibration curve. More specifically, the extraction of the contour of the separation functional layer involves, for example, binarizing the SEM image acquired in ImageJ using a known binarization method, preferably the Otsu method, appropriately selected based on the obtained image. For the contour at the contact interface between the porous support of the forward osmosis membrane and the separation functional layer, the average brightness in the horizontal direction is calculated at predetermined distances (e.g., 1 pixel) from the membrane surface toward the depth direction in the entire obtained binarized image. The average brightness is compared from the surface of the separation functional layer toward the support membrane side, and the horizontal direction of the portion with the highest average brightness is taken as the contact interface between the porous support of the forward osmosis membrane and the separation functional layer, and the straight portion thereof can be taken as the contour. Regarding the contour of the separation layer surface, in the obtained binarized image, the curve obtained by connecting the areas with contrast differences from the background with continuous lines can be considered the contour of the separation layer surface. The contour in the thickness direction of the separation layer may be the ends of the acquired image. By connecting these lines, the contour of the separation layer can be extracted.

[0042] The observation magnification of the cross-sectional image is preferably 5,000 to 30,000 times, and more preferably 10,000 times. The width of the cross-section (length in the direction parallel to the interface between the support film and the separation functional layer) is preferably about 5 to 100 μm, more preferably 5 to 50 μm, even more preferably 5 to 20 μm, and most preferably 13 μm. Furthermore, even if the contact interface between the porous support and the separation functional layer of the forward osmosis membrane is wavy, the contact interface between the porous support and the separation functional layer of the forward osmosis membrane can be uniquely identified by the method described above, unless the forward osmosis membrane is intentionally bent for observation.

[0043] [Coefficient of variation of the average thickness of the separation layer] In this embodiment, it is preferable that the coefficient of variation of the average thickness of the separation functional layer of the forward osmosis membrane is within a specific range. In this embodiment, the coefficient of variation is the value obtained by dividing the standard deviation of the average thickness by the average value of the average thickness, and is expressed as a percentage (%). The coefficient of variation of the average thickness of the separation functional layer is preferably 0 to 60%, more preferably 0 to 50%, even more preferably 0 to 40%, particularly preferably 0 to 30%, and most preferably 0 to 20%, from the viewpoint that partial functional defects of the separation functional layer are more effectively eliminated during the formation process of the separation functional layer, and the effect of the heat treatment described later is enhanced.

[0044] In this embodiment, the preferred method for measuring the average thickness and coefficient of variation of the separation functional layer is as follows. The hollow fiber membrane is divided into three equal parts along its longitudinal direction to obtain three samples. A cross-section perpendicular to the membrane surface direction (longitudinal direction) is obtained at any location on these three samples, preferably at a portion divided in half along the longitudinal direction of each sample, and microscopic observation is performed to measure the average thickness of the separation functional layer in the resulting image. This procedure is performed on three forward osmosis membranes, or three forward osmosis membranes cut from one forward osmosis membrane module, and the average thickness of the separation functional layer in a total of nine images is measured. Using the nine obtained average thickness values, the mean value and the standard deviation of the average thickness are calculated, and the coefficient of variation is calculated from these values. When cutting three forward osmosis membranes from a single forward osmosis membrane module, it is preferable to cut them from three locations: the radial outer periphery, the middle, and the center of the module. This cutting method allows for evaluation of the overall variability of the module. In the case of a flat membrane-shaped normal osmosis membrane, the membrane can be divided into nine sections to obtain nine samples, and a cross-section can be obtained from the center of each sample for microscopic observation.

[0045] The field of view of the microscope image when measuring the average thickness of the separation functional layer is preferably about 5 to 100 μm in width of the cross-section (length in the direction parallel to the interface between the support film and the separation functional layer), more preferably 5 to 50 μm, even more preferably 5 to 20 μm, and most preferably 13 μm. The magnification of the microscope image is preferably 5,000 to 30,000 times, more preferably 10,000 times.

[0046] In this embodiment, it is preferable that the structure of the support membrane and the separation functional layer of the forward osmosis membrane is uniform within the aforementioned range. If the structure of the separation functional layer and the support membrane located near the separation functional layer are uniform, the expected function and physical durability can be achieved in any part of the separation functional layer. For example, in the case of a hollow fiber-like forward osmosis membrane, the structure of the forward osmosis membrane is preferably more uniform in at least one of the circumferential and longitudinal directions, more preferably more uniform in both the circumferential and longitudinal directions, and particularly preferably more uniform in all parts of the membrane when the hollow fibers are bundled and modularized.

[0047] [Forward Osmosis Membrane and Forward Osmosis Evaluation] The forward osmosis membrane of this embodiment has high water permeability (Flux) and low salt back diffusion rate (RSF). The water permeability and salt back diffusion rate of the forward osmosis membrane in this embodiment are evaluated by performing forward osmosis treatment using purified water as the raw material solution and a 3.5% by mass aqueous sodium chloride solution as the induction solution, with each solution under conditions of 25°C. When the forward osmosis membrane has a structure having a support membrane and a separation functional layer disposed on one side of the support membrane, the water permeability may vary significantly depending on whether the raw material solution and the inducing solution are disposed on the separation functional layer side or the support membrane side, respectively. In the present embodiment, when the forward osmosis membrane is put into actual use, in order to reduce the risk of membrane contamination, it is desirable to dispose the raw material solution on the separation functional layer side and the inducing solution on the support membrane side for use. When evaluating the water permeability and the amount of salt back-diffusion of the forward osmosis membrane, it is also desirable to dispose the raw material solution on the separation functional layer side and the inducing solution on the support membrane side for evaluation so as to reflect the performance in actual use.

[0048] The amount of salt back-diffusion of the forward osmosis membrane means the amount of the inducing solute that moves from the inducing solution to the raw material solution when the raw material solution is disposed on the separation functional layer side and the inducing solution having a higher osmotic pressure than this is disposed on the support membrane side with the forward osmosis membrane interposed therebetween. The amount of salt back-diffusion (RSF) is defined by the following mathematical formula (1). [[ID=~]] RSF = G / (M×H) (1) Here, G is the amount (g) of the moved inducing solute, M is the effective membrane area (m 2 ) of the forward osmosis membrane, and H is the time (hr). The lower the amount of salt back-diffusion (RSF) of the forward osmosis membrane of the present embodiment, the more preferable. The larger the amount of salt back-diffusion, the more the amount of the inducing solute mixed into the raw material solution in the inducing solution increases; the more the amount of the solute in the raw material solution mixed into the inducing solution increases; the purity of the raw material solution concentrate decreases and its component balance is disrupted; the inducing solution is contaminated; the components in the inducing solution decrease over time; and other problems may occur. The amount of salt back-diffusion of the forward osmosis membrane of the present embodiment is, in one aspect, 2.0 g / (m 2 ×hr) or less, preferably 1.2 g / (m 2 ×hr) or less, more preferably 0.80 g / (m 2 ×hr) or less, still more preferably 0.40 g / (m 2 ×hr) or less, and particularly preferably 0.30 g / (m [[ID=~]] 2 ×hr) or less. The amount of salt back-diffusion R of the forward osmosis membrane of the present embodiment is 0.001 g / (m 2It is preferable that the salt back diffusion amount R is ≥ ×hr, and even within this range, the advantageous effects intended by the present invention will be achieved.

[0049] The permeability (Flux) of a forward osmosis membrane refers to the amount of water that moves from the raw material to the induction solution when the raw material is flowed through the separation functional layer side of the forward osmosis membrane and an induction solution with a higher osmotic pressure is placed on the support membrane side. The permeability (Flux) of a forward osmosis membrane is defined by the following formula (2). Flux = L / (M × H) (2) Here, L is the amount of water that has permeated (kg), and M is the effective surface area of ​​the forward osmosis membrane (m²). 2 ) and H is time (hr). In this embodiment, a higher water permeability (Flux) of the forward osmosis membrane is preferable. To achieve highly efficient solvent transfer, the water permeability of the forward osmosis membrane should be 1.0 kg / (m³). 2 It is preferable that it be 3.0 kg / (m²) or more, and more preferably 3.0 kg / (m²). 2 It is 5.0 kg / (m³) or more, and more preferably 5.0 kg / (m³). 2 It is 7.0 kg / (m³) or more, and particularly preferably 7.0 kg / (m³). 2 The permeability should be 50 kg / (m³) or more. On the other hand, if the water permeability is excessively high, the amount of salt back diffusion may increase, so the water permeability of the forward osmosis membrane should be 50 kg / (m³). 2 It is preferable that it is less than or equal to ×hr.

[0050] In this embodiment, salt permeability RSF / Flux (unit: g / kg), defined as the salt back diffusion rate (RSF) divided by water permeability (Flux), is an index representing the selectivity between solvent permeability and salt permeability. A lower salt permeability value indicates that salt is less likely to permeate and solvent permeability is easier. Therefore, a lower value is preferable. In conventional forward osmosis membranes, a decrease in salt back diffusion often leads to a significant decrease in water permeability, resulting in a high RSF / Flux value. However, the forward osmosis membrane of this embodiment exhibits a sufficiently low RSF / Flux value. From the viewpoint of practicality in concentrating the raw material liquid and efficient solvent transfer, the RSF / Flux value of the forward osmosis membrane in this embodiment is preferably 0.20 g / kg or less, more preferably 0.16 g / kg or less, even more preferably 0.08 g / kg or less, particularly preferably 0.06 g / kg or less, and most preferably 0.04 g / kg or less. Ideally, the RSF / Flux value is 0 g / kg, but from the viewpoint of ease of manufacturing the forward osmosis membrane, it may be, for example, 0.0001 g / kg or more.

[0051] In this embodiment, the physical durability of the forward osmosis membrane can be evaluated by applying a predetermined intermembrane pressure difference and performing a forward osmosis treatment. The intermembrane pressure differential can be applied with either side of the forward osmosis membrane considered positive. However, by applying an intermembrane pressure differential with the support membrane side and the induction solution side of the forward osmosis membrane considered positive, for example, both the forward osmosis membrane performance and physical durability can be evaluated simultaneously. In this case, pressure is applied in a direction that peels the separation functional layer away from the support membrane. Therefore, if the physical durability of the forward osmosis membrane is low, it may not be able to withstand this pressure, causing a portion of the separation functional layer to peel off from the support membrane or a portion of the separation functional layer to crack. When this happens, the separation functional layer is irreversibly altered, making it easier for the induction solution to permeate to the raw material side, resulting in a significant increase in the salt back diffusion rate and salt permeability. Therefore, by performing a forward osmosis treatment while applying a predetermined intermembrane pressure and measuring the amount of salt back diffusion and salt permeability, the degree of physical durability of the forward osmosis membrane, particularly the separation functional layer, can be investigated.

[0052] Specific methods for evaluating the physical durability of forward osmosis membranes include, for example, the following: First, purified water is used as the raw material, and a 3.5% by mass sodium chloride aqueous solution is used as the induction solution. Each solution is subjected to forward osmosis treatment for 5 minutes or more at 25°C under a reference pressure of 20 kPa in the intermembrane pressure difference, with the support membrane side and induction solution side being positive. The water permeability and salt back diffusion rate are determined and set as the reference values. Next, after thoroughly washing the forward osmosis membrane with water, the intermembrane pressure difference is changed to a predetermined pressure higher than the reference pressure, and forward osmosis treatment is performed under the same conditions as before to determine the water permeability (Flux) and salt back diffusion rate (RSF). After washing the forward osmosis membrane with water again, forward osmosis treatment is performed under the aforementioned reference pressure to determine the water permeability (Flux) and salt back diffusion rate (RSF). These values ​​are used as the water permeability and salt back diffusion rate after applying the predetermined intermembrane pressure difference, and the RSF / Flux value after applying the predetermined pressure is calculated.

[0053] The percentage obtained by dividing the reference RSF / Flux value by the RSF / Flux after applying a predetermined pressure can be evaluated as the performance retention rate (%) after applying a predetermined pressure. In the forward osmosis membrane of this embodiment, the performance retention rate after applying a predetermined intermembrane differential pressure is preferably 40% or more, and more preferably 50% or more. However, while a lower RSF / Flux value generally indicates better performance as a forward osmosis membrane, the RSF / Flux value often changes when the membrane undergoes structural or compositional changes. Therefore, comparing the physical durability of a forward osmosis membrane using the performance retention rate relative to the standard RSF / Flux value is not always appropriate. From this perspective, in this embodiment, it is more appropriate to directly compare the RSF / Flux values ​​after applying a predetermined intermembrane pressure differential. The smaller the RSF / Flux value after applying the same intermembrane pressure differential, the greater the physical durability of the forward osmosis membrane and the higher its performance as a forward osmosis membrane, and therefore the greater its practical usefulness.

[0054] A predetermined intermembrane pressure differential applied to evaluate the physical durability of a forward osmosis membrane can be, for example, 50 to 200 kPa. Specifically, by repeatedly performing forward osmosis treatment with the intermembrane pressure differential increased by 10 to 50 kPa increments, and by performing forward osmosis treatment under standard conditions, the RSF / Flux value after each applied intermembrane pressure differential can be obtained. In the forward osmosis membrane of the present invention, the RSF / Flux value after applying a differential pressure of 200 kPa between membranes is preferably 0.25 g / kg or less, more preferably 0.15 g / kg or less, even more preferably 0.10 g / kg or less, particularly preferably 0.08 g / kg or less, and most preferably 0.06 g / kg or less.

[0055] [Shape of a forward osmosis membrane] The forward osmosis membrane in this embodiment is preferably hollow fiber in shape. Hollow fiber forward osmosis membranes tend to have high performance as forward osmosis membranes because defects in the separation functional layer are reduced. Furthermore, when the forward osmosis membrane of this embodiment is used in a modularized form, it is preferable for the forward osmosis membrane to be hollow fiber in shape from the viewpoint of increasing the effective membrane area per module volume. In a hollow fiber forward osmosis membrane, it is preferable that at least one separation functional layer is located on the inner surface of the hollow fiber support membrane in order to prevent physical damage to the separation functional layer.

[0056] [Induction solution] The derivative solution exhibits a higher osmotic pressure compared to the raw material solution and is a solution that has the function of moving the solvent from the raw material solution through a forward osmosis membrane. This induction solution exhibits high osmotic pressure due to its high concentration of the induction solute. Examples of derivative solutes include alkali metal salts, alkaline earth metal salts, ammonium salts, sugars, monoalcohols, glycols, and water-soluble polymers. Specific examples of these include: Examples of alkali metal salts include sodium chloride, potassium chloride, sodium sulfate, sodium thiosulfate, and sodium sulfite; Examples of alkaline earth metal salts include magnesium chloride, calcium chloride, and magnesium sulfate; Examples of ammonium salts include ammonium chloride, ammonium sulfate, ammonium carbonate, etc. As sugars, for example, in addition to common sugars such as sucrose, fructose, and glucose, special sugars such as oligosaccharides and rare sugars are also included; Examples of monoalcohols include methanol, ethanol, 1-propanol, 2-propanol, etc. Examples of glycols include ethylene glycol, propylene glycol, etc. Examples of water-soluble polymers include polyethylene oxide, polypropylene oxide, and copolymers of ethylene oxide and propylene oxide; Each of these can be listed.

[0057] [Module] In this embodiment, the support membrane and the forward osmosis membrane can be used as a module (support membrane module or forward osmosis membrane module) containing multiple membranes within a housing. The shape of the module is not particularly limited. However, it is preferable that a compartment where the liquid comes into contact with only one surface of the membrane and a compartment where the liquid comes into contact with only the other surface of the membrane are separated by an adhesive resin that fixes the membrane to the module housing. Taking the case where the support membrane or forward osmosis membrane is in the form of a hollow fiber membrane as an example, it is preferable to have a hollow fiber membrane module in which a plurality of hollow fiber membranes are housed in a housing, and which has a configuration in which a compartment where the liquid comes into contact only with the inner surface side of the hollow fiber membrane and a compartment where the liquid comes into contact only with the outer surface side of the membrane exist in isolation. The size of the housing is not specifically defined. However, cylindrical housings with a diameter of 5 to 500 mm and a length of 20 to 10,000 mm can be used, for example. As for the adhesive resin, adhesives such as urethane-based or epoxy-based adhesives can be used.

[0058] Figure 1 shows a schematic cross-sectional view illustrating the structure of an example of a hollow fiber membrane module. The hollow fiber membrane module (1) shown in Figure 1 has a structure in which a bundle of multiple hollow fiber membranes (4) is filled into a cylindrical housing, and both ends of the bundle of hollow fiber membranes are fixed to the cylinder with adhesive fixing parts (5, 6). The housing has outer conduits (2, 3) on its sides and is sealed by headers (7, 8). Here, the adhesive fixing parts (5, 6) are solidified so as not to block the hollow portion of the hollow fiber membrane. The headers (7, 8) each have inner conduits (9, 10) that communicate with the inside (hollow portion) of the hollow fiber membrane (4) but not with the outside. Through these inner conduits (9, 10), liquid can be introduced into or removed from the inside of the hollow fiber membrane (4). The outer conduits (2, 3) each communicate with the outside of the hollow fiber membrane (4) but not with the inside. This hollow fiber membrane module (1) has a structure in which the liquid flowing inside and the liquid flowing outside come into contact only through the hollow fiber membrane (4).

[0059] [Membrane area] In this embodiment, the membrane area refers to the area of ​​the region in which the support membrane or forward osmosis membrane comes into contact with the raw material liquid and can exhibit separation function. In other words, it refers to the area of ​​the portion of the forward osmosis membrane that comes into contact with the raw material liquid or induction solution. Specifically, for example, in the case of a module of a hollow fiber membrane-like forward osmosis membrane that supplies raw material liquid to the inside, the membrane area (internal surface area of ​​the hollow fiber membrane-like forward osmosis membrane) is defined by the following formula (2), based on the length, inner diameter, and number of hollow fiber membrane-like forward osmosis membranes excluding the adhesive fixing part within the module. a = c × π × b × n (2) Here, a is the inner surface area (m²) of the hollow fiber membrane-like forward osmosis membrane. 2 ), b is the length of the hollow fiber membrane-like forward osmosis membrane excluding the adhesive fixing portion (m), c is the inner diameter of the hollow fiber membrane-like forward osmosis membrane (m), and n is the number of hollow fiber membrane-like forward osmosis membranes. For hollow fiber support membrane modules where the support membrane is in the form of hollow fibers, the internal surface area can also be calculated in accordance with the above. The length of the hollow fibers in a modularized hollow fiber support membrane or hollow fiber forward permeability membrane, excluding the adhesive-fixed portion, is sometimes referred to as the "effective length."

[0060] Method for manufacturing forward osmosis membranes The method for manufacturing a forward osmosis membrane in this embodiment may include at least a step of forming a separation functional layer, and may also include a step of manufacturing a support membrane by forming a porous support. The process for forming a porous support preferably includes a step of solidifying a resin solution, obtained by dissolving the resin in a good solvent, in a solidification bath containing a non-solvent of the resin.

[0061] <Method for manufacturing the support film> The following describes in detail the manufacturing methods for hollow fiber-like support membranes and flat-membrane-like support membranes. [Method for manufacturing hollow fiber support membranes] In this embodiment, a hollow fiber support membrane (hollow fiber membrane) consisting only of a particularly preferred hollow fiber porous support can be manufactured using a material selected from the aforementioned thermoplastic resins by known dry-wet film formation methods, melt-wet film formation methods, wet film formation methods, etc. Among these, it is preferable to manufacture it by the following method. Discharge the spinning solution from the outer channel of the double-tubular nozzle, and the internal coagulation solution from the inner channel of the double-tubular nozzle; The spinning solution discharged from the outer channel of the double-tubular nozzle is immersed in the external coagulation bath via the empty portion to coagulate it; and Applying tension to the solidified spinning solution while winding the spinning solution onto the winding solution. Includes, The aforementioned spinning solution comprises a resin (polymer) and a solvent. The temperature of the spinning solution discharged from the double-tubular nozzle is higher than the temperature of the internal coagulation solution, and the temperature difference between the two solutions is 5°C or more and less than 35°C. A method for manufacturing hollow fiber membranes. The hollow fiber membrane, after being wound onto the winding machine, may be cut to a predetermined length.

[0062] (Spinning solution) The spinning solution contains a resin (polymer) and a solvent, and is preferably a solution in which the resin is dissolved in a good solvent. In this method, a non-protic polar organic solvent such as N-methyl-2-pyrrolidone, dimethylacetamide, or dimethylformamide is preferably used as the solvent (good solvent) for the spinning solution. The spinning solution may also contain a non-solvent of the resin. As the non-solvent in the spinning solution, glycols such as polyethylene glycol and polypropylene glycol, as well as electrolytes and polyvinylpyrrolidone, can be used. Of these, glycols are preferred because they provide good spinnability and result in high-quality films. The content of the non-solvent in the spinning solution is preferably set so that the mass ratio of non-solvent / (good solvent + non-solvent) is within the range of 50-90% of the weight ratio at the compatibility limit. The compatibility limit is the point at which the polymer solution cannot become a homogeneous solution and phase separation occurs. Since the compatibility limit is generally a function of temperature, the content of the non-solvent must be set based on the compatibility limit at the spinning temperature. If the mass ratio of non-solvent / (good solvent + non-solvent) is less than 50% of the weight ratio at the miscibility limit, the viscosity of the spinning solution may be too low, resulting in poor spinnability. On the other hand, if this value exceeds 90%, the controllability of the cross-sectional shape of the hollow fiber support membrane may deteriorate. For similar reasons, the temperature of the spinning solution during the formation of the hollow fiber porous support film is preferably 30 to 80°C, and more preferably 35 to 60°C.

[0063] The polymer concentration in the spinning solution is preferably 10 to 30% by mass, more preferably 15 to 25% by mass. The polymer concentration in the spinning solution is particularly related to the strength of the resulting hollow fiber support film. When the polymer concentration in the spinning solution is within the above range, a hollow fiber support film with excellent film strength can be obtained. When preparing the spinning solution, the spinning solution may be stirred at a specified temperature for 24 hours or more, and then degassed under reduced pressure.

[0064] (Internal coagulation liquid) When forming a porous support with hollow fibers, for example, as described above, a double spinning nozzle is used, with the spinning solution being discharged from the outer cylindrical opening (outer channel) and the internal coagulation solution being discharged from the inner opening (inner channel). As the internal coagulation solution, for example, an aqueous solution can be used that mainly consists of water and contains one or more additives selected from alcohols, ethylene glycols, and amide solvents. Examples of alcohols include methanol, ethanol, and isopropyl alcohol. Examples of ethylene glycols include triethylene glycol, tetraethylene glycol, and glycerin. Examples of amide solvents include N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide. By adding such additives to the internal coagulation solution, the rate of coagulation can be controlled, making it possible to easily obtain a porous support with a desired structure. For example, adding an additive to the internal coagulation solution slows down coagulation and can reduce the pore size on the surface. However, adding too much additive to the internal coagulation solution can worsen spinning stability or coarseen the surface pore size, making it difficult to form the separation functional layer.

[0065] As the internal coagulation solution, it is preferable to use water or a mixture of water and a small amount of additive, in order to maintain spinning stability and variability of membrane performance. When glycols are added as the internal coagulation solution additive, the amount added is preferably 60% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, particularly preferably 10% by mass or less, and most preferably 5% by mass or less, relative to the total mass of the solvent contained in the internal coagulation solution. If this value exceeds 60% by mass, it becomes difficult to maintain a balance in the size of the pores on the inner and outer surfaces of the resulting hollow fiber membrane, and the pores on the inner surface tend to become particularly coarse. Using water as the internal solidification liquid is particularly preferable because it allows for the formation of a dense layer of appropriate thickness while simultaneously creating macrovoids near the surface of the porous support.

[0066] The internal coagulation solution is preferably adjusted to an appropriate temperature before being used for spinning. If the temperature of the internal coagulation solution is too high, the dense layer on the inner surface of the hollow fiber membrane becomes too thin, and the structure near the inner surface tends to become non-uniform. On the other hand, if the temperature of the internal coagulation solution is too low, the dense layer on the inner surface of the hollow fiber membrane may become too thick. If the dense layer is excessively thick, monomer supply may not be properly performed during the formation of the separation functional layer of the forward osmosis membrane, which may reduce the performance of the forward osmosis membrane, and the water permeability of the forward osmosis membrane may decrease due to the resistance of the dense layer. Based on these findings, the temperature of the internal coagulation solution is preferably 5 to 50°C, more preferably 10 to 40°C, and even more preferably 15 to 35°C.

[0067] To properly control the structure of the inner surface of the hollow fiber support membrane, it is preferable to set the temperature of the spinning solution higher than the temperature of the internal coagulation solution. More preferably, the temperature of the spinning solution should be set to 30-80°C, even more preferably to 35-60°C, the temperature of the internal coagulation solution should be set to 5-50°C, more preferably to 10-35°C, and the temperature difference between the spinning solution and the internal coagulation solution should be set to 5°C or more and less than 35°C, more preferably to 5-33°C, and even more preferably to 5-30°C. With such temperature settings, it is easier to control the structure of the inner surface of the hollow fiber membrane, the structure tends to become more uniform, and the spinning stability also tends to be higher. These temperature settings are just examples and can be adjusted as needed depending on the composition of each solution.

[0068] Furthermore, by setting the temperature of the spinning solution and the external coagulation solution within an appropriate range, it is possible to control the structure of the outer surface of the hollow fiber membrane or the surface of the flat membrane. However, the outer surface of the hollow fiber membrane and the surface of the flat membrane are susceptible to the effects of temperature rise in the spinning solution during continuous production, changes in the composition of the external coagulation solution, and atmospheric temperature and humidity. Therefore, from the viewpoint of uniformity of surface structure and ease of manufacturing, it is easier and more preferable to control the structure of the inner surface of the hollow fiber membrane. Furthermore, the internal coagulation solution used in the production of hollow fiber membranes has a low flow rate and a smaller volume compared to the coagulation bath. Therefore, when the internal coagulation solution is set to a predetermined temperature, it is possible to lower the temperature only of the surface layer of the inner surface of the hollow fiber membrane. Consequently, only the surface layer of the hollow fiber membrane can be thickened, and phase separation proceeds before macrovoids grow excessively, forming a dense layer. Furthermore, by appropriately setting the temperature difference between the spinning solution and the internal coagulation solution, the thickness of the dense layer on the inner surface of the hollow fiber membrane can be controlled. Specifically, increasing the temperature difference between the two solutions makes the lower-temperature regions on the inner surface of the hollow fiber membrane thicker, resulting in a thicker dense layer. On the other hand, decreasing the temperature difference between the two solutions makes the lower-temperature regions on the inner surface of the hollow fiber membrane thinner, resulting in a thinner dense layer. In either case, the region inside the lower-temperature surface layer has relatively lower viscosity, allowing macrovoids to grow faster than coagulation, thus forming the aforementioned macrovoid layer. For the reasons stated above, controlling the inner surface structure of the hollow fiber membrane is more preferable because it allows for easy acquisition of the desired membrane structure.

[0069] (external coagulation liquid) The spinning solution extruded from the spinneret is immersed in an external coagulation bath via the open section and coagulated. As the external coagulation solution used as the coagulation bath, one or more types selected from water, the non-solvents exemplified above, and other organic solvents can be used as additives to the internal coagulation solution. The external coagulation solution may be a liquid with the same composition as the internal coagulation solution, or a liquid with a different composition. As the external coagulation solution, it is preferable to use water, or a mixture of water and a non-solvent as an additive to the internal coagulation solution as exemplified above.

[0070] When a mixture of water and alcohol, ethylene glycols, or an amide solvent is used as the external coagulation solution, the amount of additive selected from alcohol, ethylene glycols, and amide solvents added is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 15% by mass or less, and particularly preferably 5% by mass or less, relative to the total mass of the external coagulation solution. When the amount of additive in the external coagulation solution is within this range, the coagulation on the outer surface of the hollow fiber proceeds appropriately, macrovoids of a good size are easily formed, and the shape of the hollow fiber membrane becomes uniform, which is preferable. The most preferred external coagulation solution is water. During spinning, the external coagulation solution becomes contaminated with solvents from the spinning stock that leak out from the hollow fiber membrane. Therefore, if the composition of the external coagulation solution is to be maintained within a certain range, it is necessary to refresh the external coagulation solution. Using water as the external coagulation solution is particularly preferable because it only requires continuously rinsing with water, making it easy to control the composition of the external coagulation solution.

[0071] The temperature of the coagulation bath is preferably 10 to 60°C, more preferably 20 to 50°C, and even more preferably 25 to 40°C. When the coagulation bath temperature is high, the resulting hollow fiber support membrane tends to have a looser structure, leading to higher water permeability of the hollow fiber support membrane, and consequently, higher water permeability of the forward osmosis membrane. If the coagulation bath temperature is too high, the internal and external structure of the hollow fiber support membrane is easily disturbed by thermal vibrations. As a result, the uniformity of the structure, including the surface of the hollow fiber support membrane, decreases, which can lead to defects during the flow of chemical solution in the separation functional layer formation process, and may result in increased salt back diffusion in the forward osmosis membrane. On the other hand, when the coagulation bath temperature is low, the structure of the support membrane tends to become denser, and the water permeability of the support membrane and the forward osmosis membrane tends to decrease. Lower coagulation bath temperatures increase spinning stability and tend to result in a more uniform structure of the resulting hollow fiber membrane.

[0072] In this embodiment, it is preferable that the temperature of the coagulation bath be lower than the temperature of the spinning solution. The temperature difference between the coagulation bath temperature and the spinning solution temperature is preferably 40°C or less, and more preferably 3°C or more and 40°C or less. If the temperature difference between the spinning solution and the coagulation solution is too large, or if the temperature of the coagulation bath is higher than the temperature of the spinning solution, the structure near the outer surface of the hollow fiber membrane may become non-uniform, resulting in reduced performance as a forward osmosis membrane and potentially lowering physical durability, such as making the separation functional layer more prone to peeling off in certain areas.

[0073] (idle running part) The spinning solution extruded from the spinneret passes through an empty section with a certain empty distance before reaching the coagulation bath. The empty distance from the spinneret to the coagulation bath should be adjusted appropriately according to the spinning conditions, the size of the spinneret, etc. However, from the standpoint of the structure of the hollow fiber support membrane and the uniformity of the surface pore size, the empty distance is preferably 100 to 500 mm, and more preferably 200 to 400 mm. By setting an appropriate empty distance, the overall structure of the hollow fiber support membrane is stabilized while the outer surface structure becomes moderately sparse. Therefore, when a separation functional layer is formed inside the hollow fiber to form a forward osmosis membrane, the induction solution diffuses well into the separation functional layer, which tends to increase the water permeability of the forward osmosis membrane. Furthermore, by appropriately controlling the temperature and humidity of the air-running portion, hollow fibers with a more uniform structure can be obtained. From this viewpoint, the temperature of the air-running portion is preferably 15 to 50°C, and more preferably 25 to 40°C. Also, from the viewpoint of stabilizing the overall structure of the hollow fiber support film while making the outer surface structure moderately sparse, the humidity of the air-running portion is preferably 40 to 100% relative humidity, more preferably 70 to 100%, and even more preferably 90 to 100%.

[0074] (winding up) The tension during winding of the hollow fiber membrane can be adjusted by the discharge speed of the spinning solution, the winding speed, the type and number of turn rolls, etc. The tension applied during winding of the hollow fiber membrane is preferably set appropriately, taking into consideration the composition of the spinning solution and other factors. In this embodiment, the tension during winding (unit: g) is a value measured by using a tension meter to clamp the hollow fiber membrane while it is in motion. The tension during winding of the hollow fiber membrane is preferably 4 to 60 g, more preferably 10 g or more and less than 40 g, and even more preferably 10 to 38 g, in order to prevent the yarn from breaking. A tension of 5 g or more during winding prevents meandering and slack in the hollow fiber membrane during winding, allowing for stable spinning, and resulting in less variation in the structure and properties of the resulting hollow fiber membrane, which is preferable. Furthermore, a tension of less than 40 g during winding suppresses strain in the center of the hollow fiber film thickness, allowing for higher compressive strength. The tension during winding is particularly preferably 10 g or more and 35 g or less. Maintaining the tension within this range, and appropriately adjusting the temperature and humidity of the spinning solution, pneumatic conveying section, internal coagulation solution, and external coagulation solution, spinning stability can be obtained, and the uniformity of the surface structure of the hollow fiber membrane is also improved, which is even more preferable.

[0075] [Method for manufacturing a flat membrane-shaped support film] A flat support film can be manufactured, for example, using the resin solution exemplified as being used in the manufacture of the hollow fiber support film described above, by the following method. A flat film-like support membrane consisting of a substrate and a porous support is, for example, A method of solidifying a substrate by applying a resin solution to it and then immersing it in a solidifying solution (e.g., water); A method of solidifying a substrate by immersing it in a resin solution and then immersing it in a solidifying solution (e.g., water); A method of solidifying a substrate and resin solution by extruding them into a solidifying liquid through a slit-shaped nozzle; It can be obtained by the following means. On the other hand, a flat support film consisting solely of a porous support can be obtained, for example, by coating a resin solution onto a glass substrate, immersing it in a solidifying solution to solidify it, and then peeling the solidified support film from the glass substrate. The film formation conditions, such as the composition of the resin solution and the composition of the coagulation solution, can be appropriately set by those skilled in the art, with reference to known technologies and the aforementioned methods for manufacturing hollow fiber-supported films. The flat membrane of this embodiment is more preferably a support membrane consisting solely of a porous support.

[0076] [Heat treatment] The support film obtained in the manner described above may be subjected to heat treatment. The heat treatment of the support membrane may be carried out in the same manner as the heat treatment of the forward osmosis membrane after the formation of the separation functional layer described later, or by a method that is appropriately modified by those skilled in the art.

[0077] [Process for forming the separation functional layer] A forward osmosis membrane can be obtained by forming a separation functional layer on the support membrane obtained in the manner described above. The following describes an example of a method for forming a separation functional layer, mainly composed of polyamide, on a support film. A separation functional layer mainly composed of polyamide can be formed by performing interfacial polycondensation on the surface of a porous support using an aqueous solution containing a polyfunctional amine and an organic solvent solution containing a polyfunctional acid halide. In this embodiment, a preferred method for forming the separation functional layer is, for example, to sequentially pass a first solution containing one of a polyfunctional amine and a polyfunctional acid halide, and a second solution containing the other, over a support film. It is not preferable for both the polyfunctional amine and the polyfunctional acid halide to be contained in a single solution. In this embodiment, for example, the first solution may contain a polyfunctional amine, and the second solution may contain a polyfunctional acid halide.

[0078] [Polyfunctional amines] A polyfunctional amine is an amine that has at least two primary amino groups and at least one secondary amino group in one molecule, with at least one of these amino groups being a primary amino group. Examples include aromatic polyfunctional amines such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine; aliphatic amines such as ethylenediamine and propylenediamine; and alicyclic polyfunctional amines such as 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, and 4-aminoethylpiperazine. Among these, aromatic polyfunctional amines having at least two to four primary amino groups and at least one secondary amino group in one molecule are preferred when considering separation performance, water permeability resistance, and heat resistance. Suitable polyfunctional aromatic amines include m-phenylenediamine, p-phenylenediamine, or 1,3,5-triaminobenzene. In particular, m-phenylenediamine is more preferable due to its availability and ease of handling. These polyfunctional amines can be used individually or as a mixture of two or more. When mixing two or more polyfunctional amines, the amines may be combined with each other, or with an amine having at least two secondary amino groups in one molecule. Examples of amines having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidylpropane.

[0079] [Polyfunctional acid halogens] A polyfunctional acid halide is an acid halide that has at least two halogenated carbonyl groups in one molecule. For example, Examples of trifunctional acid halides include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride. Examples of difunctional acid halides include aromatic difunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride; aliphatic difunctional acid halides such as adipoyl chloride and sebacoyl chloride; and alicyclic difunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofrancicarboxylic acid dichloride. Considering the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride. Furthermore, considering the separation performance and heat resistance of the resulting forward osmosis membrane, the polyfunctional acid chloride is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. In particular, trimesic acid chloride is preferred from the viewpoint of ease of availability and handling. These polyfunctional acid halides can be used individually or as a mixture of two or more.

[0080] [Solvent and monomer solution concentrations] The polyfunctional amine and polyfunctional acid halide are each dissolved in a suitable solvent and subjected to interfacial polycondensation as the first or second solution. The solvents for the first and second solutions are preferably those that dissolve the monomers they contain, form a liquid-liquid interface without miscibility when the two solutions come into contact, and do not damage the supporting film. Furthermore, solvents that are inert to polyfunctional amine compounds and polyfunctional acid halides are even more preferable. Examples of such solvents include the following: The solvent for the polyfunctional amine can be one or more selected from water, alcohol, etc. The solvent for the polyfunctional acid halide can be one or more selected from hydrocarbon solvents such as n-hexane, cyclohexane, n-heptane, n-octane, n-nonane, n-decane, etc.

[0081] By selecting solvents such as those described above as the solvents for the polyfunctional amine and polyfunctional acid halide, the polyfunctional amine solution and the polyfunctional acid halide solution become immiscible, allowing the interfacial polycondensation reaction to proceed and yielding a thin film of high-molecular polymer (polyamide). The composition and concentration of each solution should be set according to the type of monomer, the partition coefficient with respect to the solvent, etc., and are not particularly limited, but can be set appropriately according to the desired separation function. For example, when using an aqueous solution of m-phenylenediamine as the polyfunctional amine solution and an n-hexane solution of trimesic acid chloride as the polyfunctional acid halide solution, the appropriate monomer concentrations for interfacial polycondensation are as follows: The concentration of m-phenylenediamine is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5.0% by mass. The concentration of trimesic acid chloride is preferably 0.01 to 10% by mass, and more preferably 0.04 to 2.0% by mass. If the concentrations of these solutions are too low, the formation of the polyamide separation functional layer by interfacial polycondensation will be incomplete, leading to defects and a decrease in the separation performance when used as a forward osmosis membrane. Conversely, if the concentrations of these solutions are too high, the formed polyamide separation functional layer will become too thick, potentially reducing water permeability and increasing the amount of residual unreacted material in the separation functional layer, thus negatively impacting the performance as a forward osmosis membrane.

[0082] [Polymerization additive] The polyfunctional amine solution or polyfunctional acid halide solution may contain polymerization additives such as surfactants, organic solvents (except for organic solvents in the polyfunctional acid halide solution), organic acid salts, basic compounds, and antioxidants, provided that they do not significantly interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. Surfactants have the effect of improving the wettability of the porous support surface and reducing the interfacial tension between the amine solution and the nonpolar solvent. Organic solvents can act as catalysts for interfacial polycondensation reactions, and therefore, the addition of organic solvents may make interfacial polycondensation reactions more efficient. Organic acid salts can change the wettability of the support surface, which may result in improved film formation and improved separation performance when used as a forward osmosis membrane. Basic compounds can remove hydrogen halides produced by polymerization, which may therefore promote polymerization.

[0083] Examples of polymerization additives include surfactants such as sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, and sodium lauryl sulfate; organic solvents such as ethanol, isopropanol, N,N-dimethylformamide, and ε-caprolactam; organic acid salts consisting of amines such as triethylamine and organic acids such as camphor sulfonic acid; basic compounds such as sodium hydroxide, trisodium phosphate, and triethylamine; phenolic antioxidants, amine antioxidants, sulfuric antioxidants, phosphorus-based antioxidants, and acylation catalysts.

[0084] Furthermore, in this embodiment, it is particularly preferable to perform heat treatment (curing) after forming a polymer thin film by interfacial polycondensation. This heat treatment is presumed to improve the physical durability and solvent resistance of the polymer thin film by aligning the higher-order structure of the polymer thin film and increasing the crosslinking density, as well as reducing the amount of salt reverse diffusion in the forward osmosis membrane. In other words, it is believed that by applying heat treatment to the forward osmosis membrane in an appropriate manner, a forward osmosis membrane can be formed in which partial functional defects in the separation functional layer are reduced.

[0085] In the method for manufacturing a forward osmosis membrane according to this embodiment, it is preferable to form a support membrane having a dense layer and a macrovoid layer, which have a specific structure, and then to provide a separation function layer on the dense layer, followed by a heat treatment. Furthermore, it is even more preferable to perform the heat treatment in a wet state. Examples of heat treatment methods in a humid state include the permeation of a humid gas (e.g., nitrogen or air containing moisture) heated through a heat source, the permeation of hot water, the permeation of water vapor, and exposure to water vapor. Here, "permeation" refers to the process of supplying fluid to a forward osmosis membrane, bringing the separation functional layer and support membrane of the forward osmosis membrane into contact with the fluid. A preferred permeation method is, for example, in the case of a forward osmosis membrane using a hollow fiber support membrane consisting only of a porous support, to supply fluid to the inside or outside of the hollow fibers, or both, thereby bringing the front, back, and interior of the separation functional layer, as well as the pores of the support membrane, into contact with the fluid.

[0086] When heat treatment is performed in a dry state, the forward osmosis membrane may dry out excessively, and in particular, shrinkage of the pores in the support membrane and deformation of the support membrane may occur. If the pores of the support membrane shrink, the water permeability of the resulting forward osmosis membrane may decrease. Also, if the support membrane deforms, deformation of the separation functional layer may be induced, which may reduce the salt blocking performance of the separation functional layer and increase the amount of salt back diffusion. Therefore, when heat treatment is performed in a dry state, the heat treatment time is preferably 15 minutes or less from the viewpoint of avoiding excessive drying of the forward osmosis membrane.

[0087] In this embodiment, "heat treatment" refers to a process of heating the object to be treated to a temperature of 50°C or higher, preferably 70°C or higher. The heat treatment in this embodiment is more effective when the coefficient of variation of the thickness of the separation functional layer of the forward osmosis membrane is within the range described above. When the coefficient of variation of the thickness of the separation functional layer is within the range described above, the performance of the entire molecular functional layer can be improved by the predetermined heat treatment, and even if there is a defect in part of the separation function, its expansion can be prevented.

[0088] The heat treatment in this embodiment can be carried out by, for example, supplying hot water to the forward osmosis membrane after the separation functional layer has been formed, immersing the forward osmosis membrane in hot water after the separation functional layer has been formed, or supplying high-temperature steam to the forward osmosis membrane. Of these, it is preferable to carry out the heat treatment by supplying hot water to the forward osmosis membrane after the separation functional layer has been formed, or by supplying high-temperature steam to the forward osmosis membrane. It is preferable to supply hot water to at least the separation functional layer side of the forward osmosis membrane. This method is particularly preferable because it allows heat to be uniformly transferred to the separation functional layer and washes away residual monomers and other substances in the support membrane, making it less likely for unintended reactions to occur during the heat treatment. The temperature of the hot water is preferably 50 to 100°C, and more preferably 70 to 95°C. This type of heat treatment is preferable because the heat from the hot water is efficiently transferred to the separation functional layer, thereby promoting the crosslinking reaction of the polymer thin film constituting the separation functional layer. The hot water supply time is preferably 5 minutes to 2 hours. When the hot water supply time is 5 minutes or more, the crosslinking reaction and structural changes of the separation functional layer proceed well. However, even if hot water is supplied for more than 2 hours, the effect of the heat treatment does not increase in proportion to the hot water supply time, so the hot water supply time is preferably 2 hours or less.

[0089] When heat treatment is performed by supplying high-temperature steam to a forward osmosis membrane, "high-temperature steam" refers to gaseous water at 100°C or higher, especially under high-pressure conditions. Such high-temperature steam can generally be generated in a pressure vessel such as an autoclave used in high-pressure steam sterilization. The temperature of the high-temperature steam is preferably 100 to 160°C, and more preferably 100 to 140°C. Keeping the temperature of the high-temperature steam within this range is preferable because it promotes crosslinking reactions of the polymer thin film constituting the separation functional layer, and prevents significant damage to the support membrane, the separation functional layer, or both, resulting in an extremely low amount of salt back diffusion in the forward osmosis membrane. The time for supplying high-temperature steam to the forward osmosis membrane is preferably 1 minute to 4 hours. When the supply time is 1 minute or longer, crosslinking reactions and the like proceed well. Even if high-temperature steam is supplied for more than 4 hours, the effect of the heat treatment does not increase in proportion to the supply time of high-temperature steam, so a steam supply time of 4 hours or less is preferable.

[0090] In this embodiment, the heat treatment may consist of only one type of heat treatment, a combination of two or more types of heat treatments, or the same treatment may be repeated multiple times.

[0091] When forming a separation functional layer consisting of a polymer thin film on a support film, if at least one of the first monomer and the second monomer contains a monomer having three or more reactive groups, and the above-mentioned heat treatment in a wet state is applied to the three-dimensional polymer thin film formed therefrom, the above-mentioned effects become more pronounced. As a result, the strength and durability of the forward osmosis membrane are improved, and the amount of salt back diffusion in forward osmosis is further reduced, which is particularly preferable. [Examples]

[0092] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited in any way by these examples. Unless otherwise specified, the operations were performed at 25°C.

[0093] [Measurement of the thickness of the dense layer, as well as the size and number of voids] The thickness of the dense layer of the porous support within the support membrane, as well as the size and number of voids, were measured by observing nine electron microscope layers (cross-sectional images) obtained from the forward osmosis membrane. In the case of hollow fiber-type forward osmosis membranes, one membrane was taken from each of three locations (the radial outer periphery, the middle, and the center) of the forward osmosis membrane module (a total of three membranes). Each membrane was then divided into three equal parts along its longitudinal direction, yielding nine samples. A cross-section perpendicular to the membrane surface direction (longitudinal direction) was obtained at the center of each sample, and the resulting cross-section was observed. In the case of a flat-membrane forward osmosis membrane, each side of the membrane was divided into three equal parts, resulting in nine sections from which samples were obtained. A cross-section was then obtained from the center of each sample, and the resulting cross-sections were observed. In both the case of hollow fiber-type and flat-type forward osmosis membranes, the measured values ​​were calculated as the average value across 9 samples. For each sample, a scanning electron microscope was used to image the area near the interface where the porous support and the separation functional layer are in contact. By analyzing the obtained images (cross-sectional images), the dense layer and macrovoid layer of the porous support within the support film were identified, and the size of the voids in the macrovoid layer was determined. In this embodiment, the thickness of the dense layer of the support film, as well as the size and number of voids, were measured after the film was formed into a forward osmosis membrane. It has been confirmed that these measurements are the same within the margin of error even when measured in the support film alone.

[0094] Cross-sectional images of each sample were obtained as follows: The samples were immersed in pure water in a dedicated glass container, frozen with liquid nitrogen, and then dried by freeze-drying. Using the Broad Ion Beam (BIB) processing method (processing equipment: E-3500, Hitachi High-Tech Corporation), a cross-section perpendicular to the film plane was prepared from the dried samples, and a thin layer of osmium was coated onto it to prepare the observation samples. The observation samples were photographed using a scanning electron microscope (S-4800, Hitachi High-Tech Corporation) under the following conditions. Acceleration voltage: 1.0kV Emission current: 10μA Probe current: Normal Detector: Upper Magnification: 5,000x Pixel count: 1280 x 960 Working distance: 5.0 mm

[0095] The observation field was determined so that a 25 μm wide area of ​​the sample in the direction of the film surface was contained within the field of view. Cross-sectional images were acquired as 8-bit grayscale images under conditions that prevented luminance saturation and maximized contrast. The thickness of the dense layer of the porous support, the size of the voids, and other parameters of the resulting cross-sectional image were directly measured using a scale. The contact interface between the porous support of the forward osmosis membrane and the separation functional layer was determined by importing the obtained cross-sectional image into ImageJ (developed by the National Institutes of Health, USA), binarizing it using the Otsu method, calculating the average brightness in the horizontal direction relative to the membrane surface, and comparing the average brightness from the surface of the separation functional layer toward the support membrane side. The horizontal direction of the area with the highest average brightness was defined as the contact interface between the porous support of the forward osmosis membrane and the separation functional layer.

[0096] As an example of cross-sectional image measurement, Figures 2 and 3 show cross-sectional images of an observation sample prepared from the longitudinal center of a hollow fiber-shaped forward osmosis membrane taken from the radially intermediate portion of the forward osmosis membrane module of Example 1. Figure 2 is an electron microscope image, and Figure 3 is the same image as Figure 2 with auxiliary lines added. Figures 2 and 3 show that four macrovoids with a major axis of 1 μm or larger were observed in the entire cross-sectional image. The dense layer extended from the surface of the support film (the interface between the separation functional layer and the dense layer) to the shallowest point of the macrovoid, and its thickness was 4.7 μm. One macrovoid was observed in region A of this cross-section (the region from 0 to 5 μm deep from the interface between the separation functional layer and the dense layer). Therefore, the number of macrovoids in region A of this cross-section was 0.04 voids / μm. On the other hand, three macrovoids are observed in region B (a region with a depth of 5.0 to 10.0 μm from the interface between the separation functional layer and the dense layer). Since the width of the observation field is 25 μm, the number of macrovoids in region B of this cross-section was calculated to be 0.12 voids / μm (3 voids / 25 μm). This calculation was performed for images of nine fields of view, and the thickness of the dense layer and the number of macrovoids were calculated as the average values.

[0097] [Measurement of the average thickness and coefficient of variation of the separation layer] The average thickness and coefficient of variation of the separation functional layer were measured using the same nine samples as those used in the above-mentioned [Measurement of Dense Layer Thickness, and Void Size and Number], with a magnification of 10,000x and a field of view set so that the 13 μm width of the sample in the film plane direction was included in the field of view. The measurement was performed using nine electron microscope layers (cross-sectional images) obtained by a method similar to that used in the [Measurement of Dense Layer Thickness, and Void Size and Number]. First, the contour of the separation functional layer was extracted in each cross-sectional view using the following method. The obtained cross-sectional images were imported into image processing software (ImageJ; developed by the National Institutes of Health, USA) and binarized using the Otsu method. In the obtained binarized images, the average brightness in the horizontal direction relative to the membrane surface was calculated, and the average brightness was compared from the surface of the separation functional layer toward the support membrane side. The horizontal direction of the part with the highest average brightness was defined as the contact interface (contour) between the porous support of the forward osmosis membrane and the separation functional layer. The contour of the separation functional layer surface was defined as a curve created by connecting the parts with a contrast difference from the background in the obtained binarized image with continuous lines. The contour in the thickness direction was defined as the ends of the acquired image. By connecting these lines, the contour of the separation functional layer was extracted. The area of ​​the separation functional layer was calculated by filling in the interior of the obtained contour, and this was converted to the average thickness of the separation functional layer in one image using a calibration curve created in advance. Then, the average of the nine obtained measurements was taken as the average thickness of the separation functional layer in each comparative example, and its coefficient of variation was calculated.

[0098] [Evaluation of the resistance of the applied film-to-film differential pressure in forward osmosis performance] We investigated how forward osmosis performance is affected by the applied differential pressure between membranes. First, for each example and comparative example, the forward osmosis membrane was subjected to forward osmosis operation under the following conditions, and then the water permeability (Flux) and salt back diffusion rate (RSF) were determined, and the salt permeability (RSF / Flux) was calculated. Raw material liquid: Purified water, 25℃, membrane surface linear velocity 3cm / sec Induction solution: 3.5% by mass sodium chloride aqueous solution, 25°C, film surface velocity 3 cm / sec Intermembrane pressure difference: 20 kPa Driving time: 1 hour The forward osmosis operation was performed by adding saturated sodium chloride aqueous solution to the induction solution to maintain a constant concentration of the induction solution. The intermembrane pressure differential was set by operating the back pressure valve on the induction solution side so that the induction solution side (the support membrane side of the forward osmosis membrane) was positive (high pressure).

[0099] The salt permeability (RSF / Flux) obtained from the above measurements was used as the reference salt permeability value. After the above measurements were completed, the forward osmosis membrane was washed with water for 2 hours, and the forward osmosis treatment was repeated under the same conditions as above, except that the intermembrane pressure difference was changed to 50 kPa. Next, the forward osmosis membrane was washed with water again, and the intermembrane pressure difference was returned to 20 kPa, and the forward osmosis treatment was repeated under the same conditions as above to determine the water permeability (Flux) and salt reverse diffusion rate (RSF), and the salt permeability (RSF / Flux) was calculated. This was taken as the salt permeability value after 50 kPa operation. After the measurement was completed, the forward osmosis membrane was washed again with water, and the intermembrane pressure difference was changed to 100 kPa. The forward osmosis treatment was then repeated under the same conditions as above, and the intermembrane pressure difference was returned to 20 kPa for operation. After that, the water permeability (Flux) and salt reverse diffusion rate (RSF) were determined, and the salt permeability value after 100 kPa operation was calculated. In this manner, forward osmosis operation was performed by sequentially increasing the intermembrane pressure difference from 20 kPa to 200 kPa, interspersed with operations at 20 kPa. After each application of the intermembrane pressure difference, the salt permeability value was determined after the operation at 20 kPa. Table 3 shows the reference salt permeability value, the salt permeability value after applying 100 kPa and 200 kPa, and the performance retention rate. The performance retention rate is expressed as a percentage, calculated by dividing the reference salt permeability value by the salt permeability value after applying each intermembrane pressure difference.

[0100] [Dimensions of the support membrane] For the hollow fiber support membrane, the inner diameter, outer diameter, and film thickness were measured, while for the flat film support membrane, only the film thickness was measured. In the case of hollow fiber-supported membranes, measurements were taken using optical microscope images (cross-sectional images) of the cross-section obtained by cutting the membrane with a plane perpendicular to the membrane surface direction (longitudinal direction). The outer and inner diameters of these cross-sectional images were measured using a scale. The film thickness was calculated by dividing the difference between the outer and inner diameters by 2. Here, the outer and inner diameters refer to the outer and inner diameters of the hollow fiber, respectively. In the case of a flat support film, measurements were taken using optical microscope images (cross-sectional images) of the cross-section obtained by cutting the film with a plane perpendicular to the film surface direction. The film thickness of this cross-sectional image was measured using a scale. In this embodiment, the inner diameter, outer diameter, and film thickness of the support film were measured after it had been formed into a forward osmosis membrane. It has been confirmed that the measurements are the same within the margin of error even when measured with only the support film.

[0101] [Pure water permeability of hollow fiber-supported membranes] A hollow fiber support membrane was cut to an effective length of 10 cm, and pure water at 25°C was injected from one end. The air was then removed from the other end and the membrane was sealed. Next, an average pressure of 100 kPa (1 bar) was applied to the inside of the hollow fiber for 10 minutes to perform internal pressure filtration. The amount of filtered water was measured, and the pure water permeability per unit time per unit area of ​​the inner surface of the support membrane was calculated. Here, the hollow fiber was handled in a way that prevented it from becoming completely dry. Before measurement, the pores of the hollow fiber were wetted with a 90% by mass ethanol aqueous solution, then washed with water, and then measured. Pure water permeability was measured using a single fiber of the hollow fiber support membrane with n=5, and the average value was adopted as the measured value.

[0102] [Compressive strength of hollow fiber support membrane] A hollow fiber support membrane, cut to an effective length of 10 cm, was immersed in a pressurized container filled with 40°C pure water. One end of the hollow fiber support membrane was sealed, and the other end was connected to a nozzle leading outside the container via a syringe needle. The pressurized container was sealed, and water pressure was applied. When the pressurized pressure was maintained at 0.10 MPa for 30 seconds, the amount of water (g) that permeated into the inside of the hollow fiber was measured, and the water permeability was calculated. The above operation was repeated while increasing the pressurized pressure by 0.05 MPa increments, and the pressure at which the water permeability began to decrease was recorded. Compressive strength was measured using a single fiber of the hollow fiber support membrane with n=2, and the average value was adopted as the measured value.

[0103] [Example 1] [Fabrication of hollow fiber support membranes] A homogeneous polymer solution was prepared as the spinning stock, consisting of 19% by mass of polysulfone (Solvay Specialty Polymers, Udel-P3500), 61% by mass of N-methyl-2-pyrrolidone (Fujifilm Wako Pure Chemical Industries, Ltd.), and 20% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.). The stock solution was filled into a wet hollow fiber spinning machine equipped with a double spinning head. The stock solution at 40°C and an internal coagulation solution (water) at 25°C were discharged from the double spinning head, and the machine was run for 250 mm through air heated to 30°C with a relative humidity of 98%. After coagulation in a coagulation bath (external coagulation solution) filled with water at 30°C, the material was wound up with a tension of 30 g using a free roll as the turn roll to obtain a hollow fiber support membrane. The resulting hollow fiber support membrane had an outer diameter of 1.02 mm, an inner diameter of 0.62 mm, a film thickness of 0.20 mm, and a pure water permeability of 425 kg / m³. 2 The compressive strength was 0.79 MPa (×hr × bar). Spinning stability was good, and no significant fluctuations in the inner and outer diameters of the hollow fiber membrane were observed.

[0104] [Fabrication of support membrane modules] The 130 hollow fiber support membranes described above were cut to 120 mm lengths, filled into a cylindrical plastic housing with a diameter of 20 mm and a length of 100 mm, fixed at both ends with adhesive, cut to create an open end face, and then fitted with a header, resulting in the structure shown in Figure 1, with an effective length of 80 mm and an effective membrane inner surface area of ​​0.02 m². 2 A support membrane module was fabricated.

[0105] [Formation of the separation functional layer] An aqueous solution (first solution) containing 2.0% by mass of m-phenylenediamine and 0.15% by mass of sodium lauryl sulfate was passed through the inside of the hollow fiber support membrane in the above-mentioned support membrane module for 20 minutes. After the passage was complete, the first solution was drained by gravity from the piping at the bottom of the module. With the inside of the hollow fibers still wet with the first solution, the outside of the support membrane module was reduced to 90 kPaG (11 kPaA) and the reduced pressure was maintained for 1 minute. Then, air was passed through the inside of the hollow fibers at a linear velocity of 210 cm / sec for 1 minute to remove the excess first solution. Subsequently, an n-hexane solution (second solution) containing 0.20% by mass of trimesinate chloride was passed through the inside of the hollow fibers for 2 minutes to induce interfacial polymerization and form a separation functional layer on the inner surface of the hollow fibers. Subsequently, excess second solution was removed by flowing nitrogen gas through it, and then 85°C hot water was flowed through the inside of the hollow fiber at a linear velocity of 5 cm / sec for 30 minutes. Subsequently, the module was placed in an autoclave (AC; SX-500, manufactured by Tommy Seikou Co., Ltd.) with both ends of the hollow fiber support membrane open, and curing was performed by circulating 121°C high-temperature steam inside the autoclave for 20 minutes. Furthermore, the inside of the hollow fiber support membrane was washed with 20°C water for 30 minutes to obtain a forward osmosis membrane module. [evaluation] Various evaluations were performed using the obtained forward osmosis membrane module. Furthermore, Figures 2 and 3 show cross-sectional images of observation samples prepared from the longitudinal center of a hollow fiber-like forward osmosis membrane taken from the radially intermediate portion of the obtained forward osmosis membrane module.

[0106] [Example 2] A forward osmosis membrane module was fabricated in the same manner as in Example 1, except that a solution consisting of 98% by mass of water and 2% by mass of tetraethylene glycol was used as the internal coagulation solution, and the temperature of the internal coagulation solution was set to 30°C. Various evaluations were performed using the obtained forward osmosis membrane module.

[0107] [Example 3] In the preparation of the hollow fiber support membrane, a homogeneous polymer solution consisting of 19.2% by mass of polysulfone (Solvay Specialty Polymers, Udel-P3500), 60.5% by mass of N-methyl-2-pyrrolidone (Fujifilm Wako Pure Chemical Industries, Ltd.), and 20% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.) was used as the spinning stock, and the temperature of the internal coagulation solution was set to 20°C. A forward osmosis membrane module was then prepared in the same manner as in Example 1. Various evaluations were performed using the obtained forward osmosis membrane module.

[0108] [Example 4] In the preparation of the hollow fiber support membrane, a homogeneous polymer solution consisting of 19% by mass of polyethersulfone (BASF, Ultrason E2020P), 61% by mass of N-methyl-2-pyrrolidone (Fujifilm Wako Pure Chemical Industries, Ltd.), and 20% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.) was used as the spinning stock solution, and a solution consisting of 95% by mass of water and 5% by mass of tetraethylene glycol was used as the internal coagulation solution, and the temperature of the internal coagulation solution was set to 35°C. A forward osmosis membrane module was prepared in the same manner as in Example 1. Various evaluations were performed using the obtained forward osmosis membrane module.

[0109] [Example 5] In the fabrication of the hollow fiber-supported membrane, the temperature of the internal coagulation solution was set to 40°C and the temperature of the external coagulation solution to 35°C, and in the separation functional layer formation step, the separation functional layer was formed on the outside of the hollow fibers. In this manner, a forward osmosis membrane was fabricated in the same manner as in Example 1. In this embodiment, various measurements and evaluations were performed by appropriately changing the measurement position, pressure application direction, etc., taking into consideration that the separation functional layer is located outside the hollow fiber support membrane.

[0110] [Example 6] [Fabrication of a flat membrane-like support film] A homogeneous polymer solution was prepared consisting of 19% by mass of polysulfone (Solvay Specialty Polymers, Udel-P3500), 61% by mass of N-methyl-2-pyrrolidone (Fujifilm Wako Pure Chemical Industries, Ltd.), and 20% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.). This solution was heated to 40°C, cast onto a glass plate with a thickness of 250 μm using a doctor blade, and immediately immersed in a solidification bath filled with 10°C water for 5 minutes to solidify, thereby producing a flat film-like support membrane. The thickness of the resulting support film was 0.20 mm.

[0111] [Formation of the separation functional layer] An aqueous solution (first solution) containing 2.0% by mass of m-phenylenediamine and 0.15% by mass of sodium lauryl sulfate was dropped onto the entire surface of the flat film-shaped support film (the side not in contact with the glass plate) and left to stand for 20 minutes. Then, air was flowed horizontally across the surface of the support film for 1 minute at a linear velocity of 210 cm / sec relative to the surface of the first solution-coated surface to remove excess first solution. Subsequently, an n-hexane solution (second solution) containing 0.20% by mass of trimesinate chloride was dropped onto the entire surface of the first solution-coated surface and left to stand for 2 minutes to allow interfacial polymerization to occur, forming a separation functional layer on the porous support. Subsequently, nitrogen gas was flowed over the separation function layer formation surface to remove excess second solution, and then 85°C hot water was flowed over the separation function layer formation surface for 30 minutes at a linear velocity of 5 cm / sec. The flat membrane, after being circulated with hot water, was placed in an autoclave (SX-500, manufactured by Tommy Seikou Co., Ltd.), and high-temperature steam at 121°C was circulated inside the autoclave for 20 minutes. Furthermore, the flat membrane was washed with 20°C water for 30 minutes to obtain a flat-film-shaped forward osmosis membrane.

[0112] [Fabrication of flat membrane cells] The flat-film-like forward osmosis membrane obtained above was cut into a 140 mm x 140 mm rectangle, and a flat-film cell was fabricated by placing the flat-film-like forward osmosis membrane inside a rectangular housing with dimensions of 200 mm in length, 200 mm in width, and 300 mm in thickness.

[0113] [evaluation] Various evaluations were performed using the obtained flat membrane cells. In flat membranes, the location of the dense layer and the separation layer of the support membrane are indicated by the front and back of the membrane. Here, the back is the side that was in contact with the glass plate during the fabrication of the support membrane, and the front is the side opposite the back.

[0114] [Example 7] In the [Formation of the Separation Functional Layer], a forward osmosis membrane module was fabricated in the same manner as in Example 1, except that the vacuum on the outer part of the support membrane module after removing the first solution was changed to 10 kPaG (91 kPaA), and the time for flowing air after vacuum reduction was changed to 5 minutes. Various evaluations were performed using the obtained forward osmosis membrane module.

[0115] [Example 8] In the [Formation of the Separation Functional Layer], a separation functional layer was formed on the inner surface of the hollow fiber support membrane, and excess second solution was removed by flowing nitrogen gas through it. The module was then placed in a 50°C dryer for 5 minutes and washed with 20°C water for 30 minutes. Otherwise, a forward osmosis membrane module was fabricated in the same manner as in Example 1. Various evaluations were performed using the obtained forward osmosis membrane module.

[0116] [Example 9] In the [Preparation of Hollow Fiber Support Membrane], a homogeneous polymer solution consisting of 21% by mass of polysulfone (Solvay Specialty Polymers, Udel-P3500), 59% by mass of N-methyl-2-pyrrolidone (Fujifilm Wako Pure Chemical Industries, Ltd.), and 20% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.) was used as the spinning stock, and the temperature of the internal coagulation solution was set to 15°C. The forward osmosis membrane module was prepared in the same manner as in Example 1. Various evaluations were performed using the obtained forward osmosis membrane module.

[0117] [Comparative Example 1] [Fabrication of hollow fiber support membranes] A homogeneous polymer solution was prepared as the spinning stock, consisting of 18% by mass of hydroxylated-terminated polyethersulfone (BASF, Ultrason E2020PSR), 57% by mass of N,N-dimethylacetamide (Fujifilm Wako Pure Chemical Industries, Ltd.), and 25% by mass of tetraethylene glycol (Tokyo Chemical Industries, Ltd.). The stock solution was filled into a wet hollow fiber spinning machine equipped with a double spinning head. The stock solution at 40°C and the internal coagulation solution at 45°C were discharged from the double spinning head, and after being run for 200 mm through air heated to 30°C and with a relative humidity of 98%, the material was coagulated in a coagulation bath (external coagulation solution) filled with 50°C water. The material was then wound using a free roll as the turn roll under a tension of 10 g to obtain a hollow fiber support membrane. At this time, a solution consisting of 50% by mass of water and 50% by mass of tetraethylene glycol was used as the internal coagulation solution. The resulting hollow fiber support membrane had an outer diameter of 1.00 mm, an inner diameter of 0.70 mm, and a film thickness of 0.15 mm. The pure water permeability of the support membrane was 1,850 kg / m³. 2 The compressive strength was 0.43 MPa (×hr × bar).

[0118] [Fabrication of support membrane modules] and [Formation of separation functional layers] A forward osmosis membrane module was fabricated in the same manner as in Example 1, except that the hollow fiber support membrane described above was used. [evaluation] Various evaluations were performed using the obtained forward osmosis membrane module. Furthermore, Figures 4 and 5 show cross-sectional images of observation samples prepared from the longitudinal center of a hollow fiber-like forward osmosis membrane taken from the radially intermediate portion of the obtained forward osmosis membrane module. Figure 4 is an electron microscope image, and Figure 5 is Figure 4 with auxiliary lines added. In the forward osmosis membrane of Comparative Example 1, the density layer is thin at 0.2 μm, so the density layer is barely visible in the cross-sectional images of Figures 4 and 5. Also, in the cross-sectional image of Figure 5, the number of macrovoids in region A is listed as "0.60 voids / μm," which does not match the number of macrovoids in region A listed as "0.61 voids / μm" in Table 1. This is because the values ​​in Figure 5 are obtained from a single cross-sectional image, while the values ​​in Table 1 are the average values ​​of nine fields of view.

[0119] [Comparative Example 2] In the [fabrication of the support membrane module], a forward osmosis membrane module was fabricated in the same manner as in Example 1, except that the temperature of the internal coagulation solution was set to 37°C. Various evaluations were performed using the obtained forward osmosis membrane module.

[0120] [Comparative Example 3] In the [fabrication of the support membrane module], a forward osmosis membrane module was fabricated in the same manner as in Example 9, except that the temperature of the internal coagulation solution was set to 5°C. Various evaluations were performed using the obtained forward osmosis membrane module.

[0121] [Comparative Example 4] A forward osmosis membrane module was fabricated in the same manner as in Example 8, except that a hollow fiber support membrane module obtained in the same manner as in Comparative Example 1 was used, by forming a separation functional layer on the inner surface of the hollow fiber support membrane. Various evaluations were performed using the obtained forward osmosis membrane module.

[0122] [Comparative Example 5] [Fabrication of a flat membrane-like support film] and [Formation of a separation functional layer] A homogeneous polymer solution was prepared consisting of 20% by mass of polysulfone (Solvay Specialty Polymers, Udel-P3500) and 80% by mass of N,N-dimethylformamide (Fujifilm Wako Pure Chemical Industries, Ltd.). This solution was heated to 40°C and cast onto a glass plate using a doctor blade to a thickness of 250 μm. The solution was then immediately immersed in a solidification bath filled with 40°C water and solidified for 5 minutes to produce a flat support film. The thickness of the resulting support film was 0.20 mm. The dense layer of the fabricated support film was greater than 15 μm. A flat membrane cell containing a flat membrane-like forward osmosis membrane was prepared in the same manner as in Example 6, except that the hollow fiber support membrane obtained above was used. [evaluation] Various evaluations were performed using the obtained flat membrane cells.

[0123] [Reference examples 1~4] In the [Preparation of Hollow Fiber Support Film], the hollow fiber support film was prepared in the same manner as in Example 1, except that the winding conditions after spinning and solidifying the spinning solution were changed as shown in Table 1, and its physical properties were evaluated. In Reference Example 2, the physical properties of the hollow fibers obtained by spinning varied greatly from location to location and were unstable, resulting in poor spinning stability.

[0124] The results are shown in Tables 1-3.

[0125] [Table 1]

[0126] [Table 2]

[0127] In Table 1, the abbreviations in the Spinning Solution column represent the following: PSf: Polysulfone PES: Polyethersulfone PES-OH: Terminally hydroxylated polyethersulfone NMP:N-methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide DMF: N,N-dimethylformamide TEG: Tetraethylene glycol

[0128] [Table 3]

[0129] [Table 4]

[0130] Referring to Tables 1-3, the forward osmosis membrane modules of Examples 1-9 have high water permeability of the forward osmosis membrane. Even after being subjected to a history of intermembrane pressure differentials with the support membrane side (induction solution side) as positive, a small salt permeability (RSF / Flux) value is maintained. From this, it has been verified that the forward osmosis membranes included in the modules of Examples 1 to 9 are practical forward osmosis membranes that possess high performance as forward osmosis membranes while also having high physical durability.

[0131] In contrast to these, the forward osmosis membrane modules of Comparative Examples 1 and 4 exhibited high forward osmosis performance when the intermembrane pressure difference, with the support membrane side (induction solution side) being positive, was small. However, after being subjected to a history of high intermembrane pressure differences, the performance degradation was significant. Specifically, the forward osmosis membrane module of Comparative Example 1 showed a significant decrease in performance retention, and the forward osmosis membrane module of Comparative Example 4 showed a very large salt permeability (RSF / Flux) value. This is thought to be due to a particularly large number of macrovoids in region A and a thin density layer. This behavior is thought to be because the interface between the separation functional layer and the support membrane is unstable, and there are areas with low adhesion between the separation functional layer and the support membrane. As a result, the separation functional layer could not withstand the pressure in the direction of peeling it away from the support membrane, leading to irreversible deterioration.

[0132] Furthermore, while the number of macrovoids in region B of the forward osmosis membrane in Comparative Example 2 is appropriate, the number of macrovoids in region A is large, and the thickness of the dense layer is also thin. Therefore, even when the intermembrane differential pressure, with the support membrane side (induction solution side) as positive, is low, its performance as a forward osmosis membrane is slightly lower compared to Examples 1-3. Moreover, after being subjected to a history of high intermembrane differential pressure, the performance deteriorated significantly, and the performance retention rate was low. The slightly lower performance at low intermembrane differential pressure is thought to be because the number of macrovoids in the support membrane is inappropriate, disrupting the supply balance of each monomer during interfacial polymerization, resulting in low separation performance of the formed separation functional layer. The low performance retention rate after applying high intermembrane differential pressure is thought to be due to the thinness of the dense layer, the presence of macrovoids near the surface, etc., resulting in areas of low adhesion between the separation functional layer and the support membrane.

[0133] Furthermore, in the forward osmosis membranes of Comparative Examples 3 and 5, macrovoids were almost absent in regions A and B of the support membrane. Therefore, although the obtained forward osmosis membranes had physical durability, their performance as forward osmosis membranes was poor when the intermembrane pressure difference was small. This is thought to be because the increased density of the support membrane significantly reduced the diffusivity of the induction solution, decreasing the water permeability of the forward osmosis membrane, and consequently increasing the influence of free diffusion of salt.

[0134] From the above, it was found that in order to obtain a practical forward osmosis membrane that combines physical durability and performance as a forward osmosis membrane, it is important to control the structure of the porous support within the support membrane and the method of forming the separation functional layer. [Explanation of Symbols]

[0135] 1. Hollow fiber membrane module 2, 3 Outer conduit 4 Hollow fiber membrane 5, 6 Adhesive fixing part 7, 8 Header 9, 10 Inner conduit

Claims

1. A hollow fiber membrane comprising at least a porous support, The porous support comprises a dense layer and a macrovoid layer in this order, extending from the outer surface or inner surface in the thickness direction of the membrane wall. The macrovoid layer is a layer having macrovoids whose major axis is 1.0 μm or more. The dense layer is a layer that does not have the macrovoids. The thickness of the dense layer is 1.0 to 9.5 μm. The aforementioned macrovoid is In region A of the porous support, from the outer or inner surface to a depth of 0 to 5.0 μm, there are 0 to 0.20 particles / μm in a direction parallel to the film plane direction of the macrovoid layer, and In region B of the porous support, from the outer or inner surface to a depth of 5.0 to 10.0 μm, there are 0.04 to 0.40 particles / μm in a direction parallel to the film surface direction of the macrovoid layer. Hollow fiber membrane.

2. The hollow fiber membrane according to claim 1, wherein the macrovoids are present in region A at a rate of 0 to 0.16 per μm in a direction parallel to the film surface direction of the macrovoid layer.

3. The hollow fiber membrane according to claim 1, wherein the macrovoids are present in region B at a rate of 0.06 to 0.30 per μm in a direction parallel to the film surface direction of the macrovoid layer.

4. The hollow fiber membrane according to claim 2, wherein the macrovoids are present in region A in a direction parallel to the film surface direction of the macrovoid layer, with a density of 0 to 0.12 per μm.

5. The hollow fiber membrane according to claim 3, wherein the macrovoids are present in region B at a rate of 0.08 to 0.20 per μm in a direction parallel to the film surface direction of the macrovoid layer.

6. The hollow fiber membrane according to claim 1, wherein the number of macrovoids in region B in a direction parallel to the film surface direction of the macrovoid layer is equal to or greater than the number of macrovoids in region A in a direction parallel to the film surface direction of the macrovoid layer.

7. The hollow fiber membrane according to any one of claims 1 to 6, wherein the hollow fiber membrane consists only of the porous support.

8. The hollow fiber membrane according to any one of claims 1 to 6, wherein the thickness of the dense layer is 8.0 μm or less.

9. The hollow fiber membrane according to any one of claims 1 to 6, wherein the thickness of the dense layer is 1.5 to 6.0 μm.

10. The hollow fiber membrane according to any one of claims 1 to 6, wherein the hollow fiber membrane has the dense layer at least on the inner surface of the hollow fiber.

11. The hollow fiber membrane according to any one of claims 1 to 6, wherein the porous support comprises one or more selected from polysulfone, polyethersulfone, and derivatives thereof.

12. The hollow fiber membrane according to any one of claims 1 to 6, wherein the porous support contains polysulfone.

13. The hollow fiber membrane according to any one of claims 1 to 6, wherein the hollow fiber membrane is used as a support membrane for a forward osmosis membrane.

14. A hollow fiber membrane module comprising a housing containing a hollow fiber membrane according to any one of claims 1 to 6.

15. A method for manufacturing a hollow fiber membrane according to any one of claims 1 to 6, Discharge the spinning solution from the outer channel of the double-tubular nozzle, and the internal coagulation solution from the inner channel of the double-tubular nozzle; The spinning liquid discharged from the outer channel of the double-tubular nozzle is immersed in an external coagulation bath via the empty portion to coagulate it; and Applying tension to the solidified spinning solution while winding the spinning solution onto the winding solution. Includes, The aforementioned spinning solution contains a resin (polymer) and a solvent. The temperature of the spinning solution discharged from the double-tubular nozzle is higher than the temperature of the internal coagulation solution, and the temperature difference between the two solutions is 5°C or more and less than 35°C. The temperature of the external coagulation bath is lower than the temperature of the spinning solution discharged from the double-tubular nozzle, and the temperature difference between the two solutions is 3°C or more and 40°C or less. The distance of the aforementioned free-running portion is between 100 mm and 500 mm. A method for manufacturing hollow fiber membranes.

16. The manufacturing method according to claim 15, wherein the tension is 4 g or more and 60 g or less.

17. The manufacturing method according to claim 15, wherein the temperature of the free-running portion is 15°C or more and 60°C or less.

18. The manufacturing method according to claim 15, wherein the relative humidity of the free-running portion is 40% or more and 100% or less.

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