JP7122202B2 - Water vapor separation membrane and method for producing water vapor separation membrane - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water vapor separation membrane and a method for manufacturing a water vapor separation membrane.

In various fields such as semiconductors, secondary batteries, organic EL display devices, organic EL elements, and fuel cells, there is an increasing demand for supplying air from which water vapor has been removed (dry air). Therefore, it is desired to provide a highly efficient and highly accurate water vapor removal technique.

On the other hand, as a gas separation technique, a technique using a hollow fiber membrane is attracting attention. Gas separation technology using hollow fiber membranes is used in various fields such as air purification, separation of water vapor from air, separation of carbon dioxide from air, and separation and removal of harmful components from exhaust gas. It has been put to practical use. It is also conceivable to apply the gas separation technology using hollow fiber membranes to dry air supply technology. That is, it is conceivable to realize the supply of dry air by a water vapor removal technique using a hollow fiber water vapor separation membrane. Compared to the conventional dry air supply technology using a desiccant, the technology using such a water vapor separation membrane does not require regular chemical replacement work and does not generate waste, so costs can be reduced. I hope Furthermore, by using a hollow fiber water vapor separation membrane, the membrane area can be made larger than that of a flat membrane. For these reasons, the technique using a hollow-fiber-like water vapor separation membrane is attracting attention as a technique that can be expected to save space and save energy.

Dry air supply technology using a water vapor separation membrane provides dry air by supplying air containing a relatively large amount of water vapor (moist air) to one side of the water vapor separation membrane. Specifically, the water vapor contained in the moist air is preferentially permeated through the water vapor separation membrane, so that air with a large amount of water vapor is obtained on the other side of the water vapor separation membrane while Air with less water vapor on the side is obtained. This provides dry air. Therefore, examples of the water vapor separation membrane include a humidifying membrane as described in Patent Document 1 and a dehumidifying membrane as described in Patent Document 2.

In Patent Document 1, the sieving coefficient for dextran having a weight average molecular weight of 30000 is 0.1 or less, the sieving coefficient for dextran having a weight average molecular weight of 1200 is 0.3 or more, and the water permeability is 1.1 × Humidification membranes are described that are 10 ⁻¹¹ m ³ /m ² /s/Pa or more and 4.3×10 ⁻¹⁰ m ³ /m ² /s/Pa or less. Further, in Patent Document 1, the humidifying membrane includes a support layer having a pore length of 0.3 μm or more and a dense layer having a pore length of 0.1 μm or less and a thickness of 2.0 μm or less. is stated.

According to Patent Document 1, it is disclosed that a humidifying membrane having both high gas barrier properties and water vapor permeability and excellent durability and heat resistance can be obtained.

Patent Document 2 discloses that the average pore diameter is 8 nm or less, the water permeability is 1.0×10 ⁻⁵ ml/[cm ² ·min·(Kgf/cm ² )] or more, and the nitrogen gas permeability is 20 ml/ A porous polymeric dehumidifying membrane comprising a porous hollow fiber membrane of a water-insoluble membrane-forming polymer having a [cm ² ·min·(Kgf/cm ² )] or less is described.

Patent Document 2 discloses that a porous hollow fiber membrane obtained from a water-insoluble membrane-forming polymer and having excellent dehumidifying performance can be obtained.

JP 2007-289944 A JP-A-11-537

The water vapor separation membrane is required not only to have high gas barrier properties and water permeability, but also to have high efficiency of releasing water vapor adsorbed on the inner peripheral surface from the outer peripheral surface, that is, high purge efficiency.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency, and a method for producing the water vapor separation membrane.

As a result of various studies, the inventors of the present invention have found that the above object can be achieved by the present invention described below.

A water vapor separation membrane according to an aspect of the present invention is a porous hollow fiber water vapor separation membrane containing a hydrophilic resin, wherein the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane is equal to the outer circumference of the water vapor separation membrane. a first region in which holes having an average diameter smaller than the average diameter of the holes in the surface and smaller than the average diameter of the holes in the outer peripheral surface are formed; and a second region formed with pores having an average diameter larger than the average diameter of the pores in the first region and larger than the average diameter of the pores in the first region.

According to such a configuration, it is possible to provide a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency.

This is believed to be due to the following.

It is thought that when moist air is supplied to the inner peripheral surface side of the water vapor separation membrane, water vapor contained in the supplied moist air is adsorbed on the inner peripheral surface side of the water vapor separation membrane. Specifically, the water vapor contained in the moist air is condensed on the inner peripheral surface of the water vapor separation membrane, and the condensed moisture is contained in the water vapor separation membrane even if the pores on the inner peripheral surface are small. It is thought that the water vapor separation membrane is adsorbed on the inner peripheral surface side of the water vapor separation membrane by the hydrophilic resin. Further, in the water vapor separation membrane, a first region in which pores having an average diameter smaller than the average diameter of the pores in the outer peripheral surface are formed, and an inner peripheral surface side from the first region, the inner and a second region formed with holes having an average diameter larger than the average diameter of the pores in the peripheral surface and larger than the average diameter of the pores in the first region. For this reason, since small holes are formed in the inner peripheral surface and the first region, the hydrophilic resin contained in the water vapor separation membrane is difficult to be removed by a washing process or the like during manufacturing, and the water vapor separation membrane is hard to remove. It is believed to be favorably retained on and within the membrane of the water vapor separation membrane. In particular, it is believed that the hydrophilic resin is held between the inner peripheral surface, the first region, and therebetween. From this, it is considered that the water vapor contained in the moist air is preferably adsorbed on the inner peripheral surface side of the water vapor separation membrane.

The moisture adsorbed on the inner peripheral surface of the water vapor separation membrane is the difference in the amount of water vapor between the air supplied to the inner peripheral surface and the air present on the outer peripheral surface (difference in water vapor concentration) and the pressure on the outer peripheral surface. It is thought that the pressure difference between the inner peripheral surface side and the outer peripheral surface side due to the movement is used as a driving force to move in the cross-sectional direction of the water vapor separation membrane. That is, it is considered that the moisture adsorbed on the inner peripheral surface of the water vapor separation membrane moves from the inner peripheral surface of the water vapor separation membrane toward the outer peripheral surface. At that time, it is considered that the moving speed increases because the second region in which large pores are formed is present in the water vapor separation membrane.

After that, it is considered that the moisture moved to the outer peripheral surface of the water vapor separation membrane is released from the outer peripheral surface. It is considered that the release of moisture from the outer peripheral surface is promoted by reducing the pressure on the outer peripheral surface side of the water vapor separation membrane or by supplying dry air to the outer peripheral surface side. In addition, since the outer peripheral surface of the water vapor separation membrane is formed with pores having an average diameter larger than the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane, it is considered that moisture is easily released from the outer peripheral surface. . Further, the hydrophilic resin contained in the water vapor separation membrane is more likely to be removed by a washing process or the like during manufacturing on the outer peripheral surface side than the first region than on the other regions. Also from this, it is considered that moisture is easily released from the outer peripheral surface.

From these facts, it is considered that the water vapor separation membrane not only has high water permeability but also has high efficiency (purge efficiency) of releasing water vapor adsorbed on the inner peripheral surface from the outer peripheral surface.

On the inner peripheral surface of the water vapor separation membrane, pores having an average diameter smaller than the average diameter of the pores on the outer peripheral surface of the water vapor separation membrane are formed. Conceivable.

From the above, it is considered that a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency can be obtained.

Moreover, in the water vapor separation membrane, the average diameter of the pores on the outer peripheral surface is preferably 0.1 to 20 μm.

According to such a configuration, it is possible to provide a water vapor separation membrane having high gas barrier properties, high water permeation performance, and high purge efficiency. It is considered that this is because the moisture that has been adsorbed on the inner peripheral surface of the water vapor separation membrane and has moved through the membrane to the outer peripheral surface is more easily released from the outer peripheral surface.

Moreover, in the water vapor separation membrane, the hydrophilic resin is preferably a vinylpyrrolidone-based resin.

According to such a configuration, it is possible to provide a water vapor separation membrane having high gas barrier properties, high water permeation performance, and high purge efficiency. This is probably because the vinylpyrrolidone-based resin is highly hydrophilic, and thus the water vapor contained in the supplied moist air is more preferably adsorbed on the inner peripheral surface side of the water vapor separation membrane. .

Moreover, in the water vapor separation membrane, it is preferable that the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum of the inner peripheral surface is higher than the absorption intensity of the outer peripheral surface.

According to such a configuration, it is possible to provide a water vapor separation membrane having high gas barrier properties, high water permeation performance, and high purge efficiency.

This is believed to be due to the following.

First, the above relationship of the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum indicates that more hydrophilic resin is present on the inner peripheral surface than the hydrophilic resin present on the outer peripheral surface. it is conceivable that. That is, it is considered that the hydrophilic resin contained in the inner peripheral surface side of the water vapor separation membrane is large and the hydrophilic resin contained in the outer peripheral surface side of the water vapor separation membrane is small.

Since the hydrophilic resin contained on the inner peripheral surface side of the water vapor separation membrane is large, the water vapor contained in the supplied moist air is more preferably adsorbed on the inner peripheral surface side of the water vapor separation membrane. it is conceivable that.

Since the amount of hydrophilic resin contained on the outer peripheral surface side of the water vapor separation membrane is small, it is considered that moisture is more likely to be released from the outer peripheral surface.

From these facts, it is considered that a water vapor separation membrane having high gas barrier properties, higher water permeation performance and higher purge efficiency can be obtained.

Moreover, in the water vapor separation membrane, it is preferable that the permeation flux of air is 0 LMH/bar or more and less than 5000 LMH/bar.

According to such a configuration, it is possible to obtain a water vapor separation membrane having not only high water permeation performance and purge efficiency, but also higher gas barrier properties. With such a water vapor separation membrane, movement of gases other than water vapor is suppressed, and water vapor can be separated more preferentially.

Further, a method for producing a water vapor separation membrane according to another aspect of the present invention is the method for producing the water vapor separation membrane, wherein a membrane-forming stock solution containing a resin constituting the water vapor separation membrane and a solvent is prepared. a step of forming the membrane-forming undiluted solution in the form of hollow fibers; a passing step of passing the membrane-forming undiluted solution formed in the form of hollow fibers through a humidified space; and a membrane-forming undiluted solution that has passed through the humidified space. and contacting with an external coagulation liquid.

According to such a configuration, it is possible to suitably manufacture a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency.

This is believed to be due to the following.

First, a membrane-forming stock solution containing a resin constituting the water vapor separation membrane and a solvent is prepared, the obtained membrane-forming stock solution is formed into hollow fibers, and then the membrane-forming stock solution formed into hollow fibers is humidified. When it is passed through the humidified space, the membrane-forming undiluted solution formed in the form of hollow fibers is brought into contact with the moisture existing in the humidified space. As a result, phase separation occurs from the outer peripheral surface side of the membrane-forming stock solution formed in the form of hollow fibers, relatively large pores are formed near the outer peripheral surface side, and relatively small pores are formed inside the pores to solidify. is considered to be On the other hand, since only the moisture present in the humidified space comes into contact with the membrane-forming undiluted solution formed in the form of hollow fibers, it is thought that the amount of contact is small and the inner peripheral surface does not solidify. It is considered that this forms the area from the outer peripheral surface to the vicinity of the first region. That is, the average diameter of the holes on the outer peripheral surface is larger than the average diameter of the holes on the inner peripheral surface, and the holes are formed that are larger than the average diameter of the holes on the first region, and further, the inner side near the outer peripheral surface is formed. It is considered that a water vapor separation membrane having the first region is formed in the .

After that, when the membrane-forming undiluted solution that has passed through the humidified space is brought into contact with the external coagulating liquid, phase separation occurs in the region that was not coagulated in the previous phase separation, and it is thought that the inner peripheral surface is coagulated. . At that time, it is believed that solidification is performed so that a relatively large hole is formed inside the first region, a relatively small hole is formed inside the first region, and a smaller hole is formed on the inner peripheral surface. . It is considered that this forms the first region to the inner peripheral surface. That is, inside the first region, a second region larger than the average diameter of the holes in the inner peripheral surface and larger than the average diameter of the holes in the first region is formed, and further inside the second region, the outer peripheral surface It is thought that an inner peripheral surface having holes smaller than the average diameter of the holes in is formed.

From the above, it is considered that a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency can be produced.

Further, in the method for producing a water vapor separation membrane, the space preferably has a temperature of 20° C. or more and less than 80° C. and a relative humidity of 30 to 100% RH.

According to such a configuration, it is possible to more preferably manufacture a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency. It is considered that this is because the phase separation in the passing step is performed more favorably.

Moreover, in the method for producing a water vapor separation membrane, it is preferable that in the passing step, the time for passing through the space is 0.2 seconds or more and less than 20 seconds.

According to such a configuration, it is possible to more preferably manufacture a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency. It is considered that this is because the phase separation in the passing step is performed more favorably.

According to the present invention, it is possible to provide a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency, and a method for producing the water vapor separation membrane.

FIG. 1 is a diagram showing a scanning electron micrograph of a cross section of a water vapor separation membrane according to an embodiment of the present invention. FIG. 2 is a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the water vapor separation membrane according to the embodiment of the present invention. FIG. 3 is a diagram showing a scanning electron micrograph of the outer peripheral surface of the water vapor separation membrane according to the embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the position in the membrane and the average diameter of the pores at that position in the water vapor separation membrane according to the embodiment of the present invention. FIG. 5 is a partial perspective view of a water vapor separation membrane according to an embodiment of the invention. FIG. 6 is a schematic diagram showing an example of a hollow fiber molding nozzle used in the manufacturing method according to the embodiment of the present invention. FIG. 7 is a diagram showing a scanning electron micrograph of a cross section of a water vapor separation membrane according to a comparative example. FIG. 8 is a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the water vapor separation membrane according to the comparative example. FIG. 9 is a scanning electron micrograph of the outer peripheral surface of a water vapor separation membrane according to a comparative example.

As a result of studies by the present inventors, conventional water vapor separation membranes, such as the humidifying membrane described in Patent Document 1 and the porous polymer dehumidification membrane described in Patent Document 2, are actually used as water vapor separation membranes. In this case, the water vapor permeation performance was sometimes lower than the water permeation performance. In other words, the conventional water vapor separation membrane may have a low efficiency (purge efficiency) for releasing water vapor adsorbed on the inner peripheral surface from the outer peripheral surface.

Specifically, in Patent Document 1, although the water permeability of the humidifying membrane and the presence or absence of air leaks are evaluated, the water vapor permeability is not particularly evaluated. Further, it is disclosed that the porous polymer dehumidifying membrane described in Patent Document 2 has a high water permeability and a low nitrogen gas permeability. Therefore, the porous polymer dehumidifying membrane described in Patent Document 2 is considered to have high water permeability and high gas barrier properties, but Patent Document 2 does not particularly evaluate the water vapor permeability performance. Based on these facts, it is considered that in Patent Documents 1 and 2, the performance of the water vapor separation membrane is evaluated in terms of water permeation performance and gas barrier property. Even if the humidifying membrane described in Patent Document 1 and the porous polymer dehumidifying membrane described in Patent Document 2 have high gas barrier properties and high water permeation performance, as described above, the water permeation performance is poor. In some cases, the water vapor transmission performance was low.

Therefore, when the water vapor is allowed to permeate through the water vapor separation membrane, as described above, it is thought that the moisture adsorbed on the inner peripheral surface side moves within the membrane and is released on the outer peripheral surface side. The present inventors speculated that the release process on the outer peripheral surface side is rate-determining. Considering that conventional water vapor separation membranes do not have a structure that increases the rate at which water is released from the membrane on the outer peripheral side, we investigated a structure for water vapor separation membranes that would increase this rate. As a result, it was found that the above object of providing a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency can be achieved by the present invention described below.

Embodiments according to the present invention will be described below, but the present invention is not limited to these.

A water vapor separation membrane according to an embodiment of the present invention is a porous hollow fiber water vapor separation membrane containing a hydrophilic resin. That is, the water vapor separation membrane is a membrane containing a hydrophilic resin and is a porous hollow fiber membrane. Regarding the water vapor separation membrane, the relationship between the position of the pores present in the membrane and the size of the pores at each position is as follows.

First, as shown in FIGS. 1 to 4, in the water vapor separation membrane 10, the average diameter of the pores on the inner peripheral surface 11 is smaller than the average diameter of the pores on the outer peripheral surface 12. FIG. The water vapor separation membrane 10 has a first region 13 in which pores having an average diameter smaller than the average diameter of the pores in the outer peripheral surface 12 are formed, and an inner peripheral surface 11 side of the first region 13, the inner and a second region 14 formed with holes having an average diameter larger than the average diameter of the holes in the peripheral surface 11 and larger than the average diameter of the holes in the first region 13 . That is, the water vapor separation membrane 10 has the first region 13 and the second region 14 in order from the outer peripheral surface 12 toward the inner peripheral surface 11 . The relationship between the structures of the outer peripheral surface 12, the first region 13, the second region 14, and the inner peripheral surface 11 in the water vapor separation membrane 10 and the average diameter of the pores is determined by the longitudinal direction of the water vapor separation membrane 10. It can be confirmed by observing a cross section, which is a plane perpendicular to the direction, with an electron microscope.

In addition, FIG. 1 is a view showing a scanning electron micrograph of a cross section (a plane perpendicular to the longitudinal direction of the water vapor separation membrane) of the water vapor separation membrane 10 according to the present embodiment. FIG. 2 is a scanning electron micrograph of the vicinity of the outer peripheral surface 12 in the cross section of the water vapor separation membrane 10 according to this embodiment. FIG. 3 is a diagram showing a scanning electron micrograph of the outer peripheral surface 12 of the water vapor separation membrane 10 according to this embodiment.

FIG. 4 is a diagram showing the relationship between the position in the membrane and the average diameter of the pores at that position in the water vapor separation membrane 10 according to this embodiment. In FIG. 4, the x-axis indicates the position within the membrane, that is, the distance from the outer peripheral surface 12 of the water vapor separation membrane 10 toward the inner peripheral surface 11 from the outer peripheral surface 12 . Also, in FIG. 4, the y-axis indicates the average diameter of the pores formed at each position in the membrane.

The results shown in FIGS. 1 to 4 are based on Example 2 below.

As shown in FIG. 4, the water vapor separation membrane 10 has a function with the distance from the outer peripheral surface 12 of the water vapor separation membrane 10 as the x axis and the average diameter of the pores in the water vapor separation membrane 10 as the y axis. It has a local minimum and a local maximum. The position of the minimum value corresponds to the first region 13 , and the position of the maximum value corresponds to the second region 14 . That is, in the water vapor separation membrane 10, the average diameter of the pores in the water vapor separation membrane 10 gradually decreases from the outer peripheral surface 12 side toward the inner peripheral surface 11 side, and then gradually increases, After that, it has a structure that becomes progressively smaller.

From the above, the water vapor separation membrane 10 includes, in order from the outer peripheral surface 12 toward the inner peripheral surface 11, a layer (first coarse layer) near the outer peripheral surface 12 including the outer peripheral surface 12, and the first coarse layer. A layer near one region (first dense layer), a layer near the second region (second coarse layer), and a layer near the inner peripheral surface 11 including the inner peripheral surface 11 (second dense layer: separation layer).

The first coarse layer is a layer near the outer peripheral surface 12 including the outer peripheral surface 12 as described above. The outer peripheral surface 12 releases moisture that has been absorbed by the inner peripheral surface 11 and has passed through the second region 14 and the first region 13 to the outside. For this reason, the outer peripheral surface 12 is the surface most affected by the driving force, for example, the reduced pressure and dry air from the outside when releasing this moisture to the outside. Therefore, it is preferable that the first coarse layer including the outer peripheral surface 12 has a property of easily releasing moisture.

The average diameter of the pores in the outer peripheral surface 12 is preferably 0.1 to 20 μm, more preferably 0.5 to 20 μm, even more preferably 0.5 to 10 μm. Also, the first coarse layer tends to increase in size as the formed hole approaches the outer peripheral surface 12 . Therefore, in the first coarse layer, the maximum value of the average diameters of the pores formed in each film thickness direction is the average diameter of the pores in the outer peripheral surface 12 . Accordingly, the maximum value of the first coarse layer is preferably 0.1 to 20 μm, more preferably 0.5 to 20 μm, even more preferably 0.5 to 10 μm. If the pores formed in the first coarse layer are too small, it tends to be difficult to release the moisture in the film to the outside. It is considered that this is because the driving force is not sufficiently transmitted in the thickness direction. Therefore, it is considered that the purge efficiency is lowered. Also, if the pores formed in the first coarse layer are too large, there is a tendency that the water vapor separation membrane cannot be produced favorably.

In addition, the average diameter of the holes in the outer peripheral surface 12 can be measured, for example, as follows. The outer peripheral surface of the water vapor separation membrane is subjected to a magnification that makes it easy to understand the size of the pores (for example, a magnification of 5000 times, etc.). An image (e.g., FIG. 3) taken with a scanning electron microscope at 20°C is binarized using image measurement software (Image-Pro Plus manufactured by Planetron Co., Ltd.) to obtain the pore area distribution. . From the obtained area, the diameter when the pores are considered to be a perfect circle is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average diameter of the pores on the outer peripheral surface of the water vapor separation membrane (the above defined as the maximum value in the first coarse layer).

It is preferable that the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum of the outer peripheral surface 12 is weaker than that of the inner peripheral surface 11 . That is, in the water vapor separation membrane 10 , the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum of the inner peripheral surface 11 is preferably higher than that of the outer peripheral surface 12 . In addition, the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum of the inner peripheral surface 11 is more than 1.5 times and less than 20 times the absorption intensity of the outer peripheral surface 12. is preferably 2 times or more and less than 20 times, and more preferably 2 times or more and 10 times or less. The above relationship of the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum is considered to represent that more hydrophilic resin is present on the inner peripheral surface than the hydrophilic resin present on the outer peripheral surface. be done. That is, it is considered that the hydrophilic resin contained in the inner peripheral surface side of the water vapor separation membrane is large and the hydrophilic resin contained in the outer peripheral surface side of the water vapor separation membrane is small. That is, the hydrophilic resin present on the outer peripheral surface 12 is less than the hydrophilic resin present on the inner peripheral surface 11 . From this, it is considered that even if the water vapor separation membrane 10 contains a hydrophilic resin, moisture is likely to be released from the outer peripheral surface 12 . On the other hand, if the absorption strength of the outer peripheral surface 12 is too high, it means that there is too much hydrophilic resin present on the outer peripheral surface 12, which tends to make it difficult to release the moisture in the film to the outside. On the other hand, if the absorption strength of the outer peripheral surface 12 is too weak, it means that the amount of hydrophilic resin present on the outer peripheral surface 12 is too small. Therefore, if the relationship of the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum is the above relationship, first, the hydrophilic resin contained on the inner peripheral surface 11 side of the water vapor separation membrane 10 is Therefore, it is considered that the water vapor contained in the supplied moist air is more preferably adsorbed on the inner peripheral surface 11 side of the water vapor separation membrane 10 . In addition, since the amount of hydrophilic resin contained on the outer peripheral surface 12 side of the water vapor separation membrane 10 is small, it is considered that moisture is more likely to be released from the outer peripheral surface 12 . From these facts, it is considered that a water vapor separation membrane having high gas barrier properties, higher water permeation performance and higher purge efficiency can be obtained.

The infrared absorption spectrum here is not particularly limited as long as it is a spectrum obtained by infrared spectroscopy. Specifically, a general infrared spectrophotometer (for example, JIR-5500 manufactured by JEOL Ltd.) is used to measure the inner and outer peripheral surfaces of the water vapor separation film by a single reflection ATR method. Infrared absorption spectrum and the like obtained when The absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum includes, for example, the absorption intensity around 1671 cm ⁻¹ .

The first dense layer is a layer near the first region 13 in which holes having an average diameter smaller than the average diameter of the pores in the outer peripheral surface 12 and smaller than the average diameter of the pores in the second region 14 are formed. If there is, it is not particularly limited. Further, the first region 13 is not particularly limited as long as holes having an average diameter smaller than the average diameter of the holes in the outer peripheral surface 12 and smaller than the average diameter of the holes in the second region 14 are formed. Specifically, the average diameter of the pores in the first region 13 is preferably 0.01 to 1.0 μm, more preferably 0.01 to 0.8 μm, and more preferably 0.01 to 0.8 μm. More preferably, it is 5 μm. In addition, since the minimum value of the average diameters of the pores formed in the first dense layer in each film thickness direction is the average diameter of the pores in the first region 13, the above-mentioned The minimum value is preferably 0.01 to 1.0 μm, more preferably 0.01 to 0.8 μm, even more preferably 0.01 to 0.5 μm. If the holes in the first region 13 or the holes formed in the first dense layer are too small, the dehumidifying performance tends to be lowered. It is considered that this is because the movement speed of moisture in the first dense layer becomes too slow. Moreover, if the pores in the first region 13 or the pores formed in the first dense layer are too large, the difference in size between the pores in the first coarse layer and the second coarse layer becomes too small, which is preferable. The first dense layer is not formed, and the outflow suppressing effect of the hydrophilic resin tends to be insufficient.

Moreover, the average diameter of the pores in the first region 13, that is, the minimum value in the first dense layer can be measured, for example, as follows. The first dense layer in the cross section of the water vapor separation membrane (the plane perpendicular to the longitudinal direction of the water vapor separation membrane) is measured at a magnification that makes it easy to understand the size of the pores (for example, a magnification of 5000 times, etc.). An image taken with a scanning electron microscope at a magnification of 2000 times or 1000 times depending on the size is measured using image measurement software (Image-Pro Plus manufactured by Planetron Co., Ltd.). to obtain the pore area distribution. From the obtained area, the diameter when the pores are considered to be perfect circles is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average of the pores in the first region 13 of the water vapor separation membrane. Defined as the diameter (said minimum value in said first dense layer). Then, the average value is calculated at a plurality of locations in the thickness direction of the first dense layer observed in the same cross section, and the minimum value is the minimum value in the first dense layer (the number of holes in the first region 13). average diameter).

The second coarse layer is a layer near the second region 14 in which holes having an average diameter larger than the average diameter of the pores in the inner peripheral surface 11 and larger than the average diameter of the pores in the first region 13 are formed. If so, it is not particularly limited. Moreover, the second region 14 is not particularly limited as long as the holes having an average diameter larger than the average diameter of the holes in the inner peripheral surface 11 and larger than the average diameter of the holes in the first region 13 are formed. Specifically, the average diameter of the pores in the second region 14 is preferably 1 to 20 μm, more preferably 1 to 15 μm, even more preferably 1 to 10 μm. In addition, since the maximum value of the average diameters of the pores formed in the second coarse layer in each film thickness direction is the average diameter of the pores in the second region 14, the above-mentioned The maximum value is preferably 1 to 20 μm, more preferably 1 to 15 μm, even more preferably 1 to 10 μm. If the holes in the second region 14 or the holes formed in the second coarse layer are too small, the dehumidifying performance tends to be lowered. It is considered that this is because the moving speed of water in the second coarse layer becomes too slow. Specifically, when the pores in the second region 14 and the pores formed in the second coarse layer are smaller than the average diameter of the pores in the inner peripheral surface 11, the movement speed of moisture in the second coarse layer is reduced. It is believed that it is unable to do so sufficiently to enhance the effect. Further, if the pores in the second region 14 or the pores formed in the second coarse layer are too large, the strength of the membrane may be lowered, or the hydrophilic resin may be retained in the separation layer, which is the second dense layer. There is a tendency to not be able to perform functions sufficiently.

The average diameter of the pores in the second region 14, that is, the maximum value in the second coarse layer can be measured by the same method as the minimum value in the first dense layer. That is, the second coarse layer in the cross section of the water vapor separation membrane (the plane perpendicular to the longitudinal direction of the water vapor separation membrane) is measured at a magnification that makes it easy to understand the size of the pores (for example, a magnification of 5000 times, etc.). An image taken with a scanning electron microscope at a magnification of 2000 times or 1000 times depending on the size of the hole is measured using image measurement software (Image-Pro manufactured by Planetron Co., Ltd.). Plus) to obtain the pore area distribution. From the obtained area, the diameter when the pores are regarded as perfect circles is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average of the pores in the second region 14 of the water vapor separation membrane. It is defined as the diameter (the maximum value in the second coarse layer). Then, the average value is calculated at a plurality of locations in the film thickness direction of the second coarse layer observed in the same cross section, and the maximum value is the maximum value in the second coarse layer (the number of holes in the second region 14). average diameter).

The second dense layer (separation layer) is a layer near the inner peripheral surface 11 including the inner peripheral surface 11 . The separation layer including the inner peripheral surface 11 is a layer that suppresses permeation of gases other than water vapor, that is, exerts gas barrier properties, and furthermore, incorporates water vapor into the film.

The average diameter of the pores in the inner peripheral surface 11 is preferably 1 to 100 nm, more preferably 1 to 50 nm, even more preferably 1 to 30 nm. In addition, the second dense layer (separation layer) tends to become smaller as the formed holes approach the inner peripheral surface 11 . Therefore, the minimum value among the average diameters of the pores formed in the second dense layer (separation layer) in each film thickness direction is the average diameter of the pores in the inner peripheral surface 11 . Therefore, the minimum value of the second dense layer (separation layer) is preferably 1 to 100 nm, more preferably 1 to 50 nm, even more preferably 1 to 30 nm. If the pores in the inner peripheral surface 11 or the pores formed in the second dense layer (separation layer) are too large, the gas barrier property cannot be sufficiently exhibited, that is, the tendency that the permeation of gases other than water vapor cannot be sufficiently suppressed. There is If the gas barrier property cannot be exhibited sufficiently, it cannot function as a dehumidification film. Further, the smaller the pores in the inner peripheral surface 11 and the pores formed in the second dense layer (separation layer), the better, but in practice, the limit is about 1 nm. For this reason, the average diameter of the pores in the inner peripheral surface 11 and the minimum value in the second dense layer (separation layer) are preferably within the above ranges.

The average diameter of the pores in the inner peripheral surface 11, that is, the minimum value in the second dense layer (separation layer) can be measured from the removal rate of dextran dispersed in water, for example, as follows. . A membrane module is prepared by using 30 water vapor separation membranes with an effective membrane length of 20 cm. Using this membrane module, a liquid in which dextran is dispersed is allowed to permeate, and the rejection is measured. As the dextrans, at least two kinds of dextrans having different molecular weights (for example, dextran-40 and dextran-70 manufactured by Tokyo Kasei Kogyo Co., Ltd.) are used, and the rejection rate by the water vapor separation membrane is 90%. Determine the molecular weight of the dextran at time. The Stokes diameter is calculated from the obtained molecular weight using the following Stokes formula, and this Stokes diameter is defined as the average diameter of the pores in the inner peripheral surface 11, that is, the minimum value in the second dense layer (separation layer). do.

The Stokes formula is the following formula.

Rs=2KT/(6πηD)
In the above formula, Rs represents the Stokes diameter. K indicates the Boltzmann coefficient and is 1.381×10 ⁻²³ . In addition, K is 298 ° C., which is the absolute temperature, η indicates the viscosity of the solvent, which is 0.00089 Pa s, and D = 8.76 × 10 ^-9 × (Mw: weight average molecular weight) ^{-0 .48} .

The permeation performance of the water vapor separation membrane is preferably as follows, for example.

The water vapor separation membrane preferably has an air permeation flux (air leak amount) of 0 LMH/bar or more and less than 5000 LMH/bar, more preferably 0 to 3000 LMH/bar, and 0 to 500 LMH/bar. is more preferred, and 0 LMH/bar is most preferred. If the amount of air leakage is too large, the gas barrier property tends to deteriorate, and the water vapor separation membrane tends to fail to function sufficiently. Further, the air leak amount is preferably as small as possible, and therefore, as described above, 0LMH is most preferable.

In addition, the permeation flux of air is obtained, for example, as follows. Prepare a membrane module using a water vapor separation membrane with an effective length of 20 cm with one end sealed, filter air under the conditions of a predetermined filtration pressure and temperature of 25 ° C., and measure the permeation amount of air per hour. . From this measured permeation amount, the permeation amount per unit membrane area, unit time, unit pressure, and 1 bar (0.1 MPa) is converted into permeation flux (L/m ² /h/bar: LMH/bar). obtain.

In addition, the water vapor separation membrane preferably has a water permeation flux (water permeability) at a transmembrane pressure difference of 0.1 MPa, preferably 1 to 1000 LMH, more preferably 1 to 800 LMH, and 1 to 600 LMH. It is even more preferable to have If the water permeability is too high, the gas barrier properties tend to deteriorate, so the water vapor separation membrane tends to fail to function sufficiently. On the other hand, if the water permeability is too low, the moisture transfer speed in the membrane tends to be too slow, making it difficult to function as a water vapor separation membrane.

The permeation flux of water at a transmembrane pressure difference of 0.1 MPa is obtained, for example, as follows. Prepare a membrane module using a water vapor separation membrane with an effective length of 20 cm with one end sealed, filter pure water under conditions of a filtration pressure of 0.1 MPa and a temperature of 25 ° C., and measure the water permeation rate per hour. do. From this measured water permeation rate, the water permeation rate per unit membrane area, unit time, and unit pressure is converted to obtain the water permeation flux (L/m ² /h: LMH) at a transmembrane pressure difference of 0.1 MPa. . The permeation flux of water here is the permeation flux of water at a transmembrane pressure difference of 0.1 MPa, so it is LMH/bar.

It is preferable that the water vapor separation membrane is free of macrovoids. A macrovoid is a defective portion in the water vapor separation membrane, and is, for example, a pore having a pore size exceeding 20 μm.

The water vapor separation membrane has a hollow fiber shape and may be open on one side in the longitudinal direction and may be open or closed on the other side. Examples of the shape of the water vapor separation membrane include shapes such as those shown in FIG. FIG. 5 is a partial perspective view showing an example of the water vapor separation membrane according to this embodiment.

The outer diameter R1 of the water vapor separation membrane is preferably 200 to 1500 μm, more preferably 200 to 1000 μm, even more preferably 200 to 900 μm. If the outer diameter is too small, the inner diameter of the water vapor separation membrane tends to be small, resulting in increased ventilation resistance and a tendency to fail to secure a sufficient flow rate. On the other hand, if the outer diameter is too large, the inner diameter of the water vapor separation membrane tends to increase, and the shape of the hollow fiber membrane cannot be maintained, and the membrane tends to be easily crushed or distorted. In addition, the bursting pressure of the water vapor separation membrane is lowered, and there is a tendency that sufficient pressure resistance strength cannot be secured as the water vapor separation membrane. Furthermore, the membrane area per unit volume of the module tends to decrease, leading to a decrease in module efficiency. If it is the above outer diameters, it is a suitable size as a water vapor separation membrane provided for the apparatus which implement|achieves the separation technique using a water vapor separation membrane.

The inner diameter R2 of the water vapor separation membrane is preferably 100 to 750 μm, preferably 100 to 700 μm, more preferably 100 to 650 μm. If the inner diameter is too small, there is a tendency that ventilation resistance increases and sufficient flow rate cannot be ensured. On the other hand, if the inner diameter is too large, the outer diameter tends to be too large, and the shape of the hollow fiber membrane cannot be maintained, and the membrane tends to be easily crushed or distorted. In addition, the bursting pressure of the water vapor separation membrane is lowered, and there is a tendency that sufficient pressure resistance strength cannot be secured as the water vapor separation membrane. Furthermore, the membrane area per unit volume of the module tends to decrease, leading to a decrease in module efficiency. The inner diameter as described above is a suitable size for a water vapor separation membrane provided in an apparatus that realizes separation technology using a water vapor separation membrane.

The film thickness T of the water vapor separation membrane is 50 to 500 μm, more preferably 50 to 400 μm, even more preferably 50 to 300 μm. If the film thickness is too thin, there is a tendency that deformation such as distortion tends to occur due to insufficient strength. On the other hand, if the film thickness is too thick, it tends to be difficult to obtain a suitable film structure, such as difficulty in suppressing the occurrence of macrovoids. In some cases, the strength may decrease.

If the outer diameter R1, the inner diameter R2, and the film thickness T of the water vapor separation membrane are within the above ranges, the water vapor separation membrane has a suitable size as a water vapor separation membrane provided in an apparatus that realizes separation technology using a water vapor separation membrane. Therefore, the size of the device can be reduced.

The strength of the water vapor separation membrane is not particularly limited as long as it can be used as a water vapor separation membrane. Specifically, the strength of the water vapor separation membrane is preferably 1 to 20 MPa, more preferably 1 to 15 MPa, further preferably 1 to 10 MPa in terms of pressure resistance (bursting strength). If the strength is too low, there is a tendency that it cannot be practically used as a water vapor separation membrane. That is, since the water vapor separation membrane usually supplies pressurized moist air to the inner peripheral surface side and decompresses the outer peripheral surface side (secondary side) in many cases, a sufficiently high pressure resistance is required. tend not to satisfy it. If the intensity is too high, there is fluorescence that reduces the water vapor transmission performance. As for the strength of the water vapor separation membrane, if the pressure resistance is within the above range, it can be suitably used as a water vapor separation membrane.

In addition, the pressure resistance (bursting strength) is measured by preparing a membrane module using a water vapor separation membrane with one end of the water vapor separation membrane sealed and the other end left open, and applying it to the inner peripheral side of the water vapor separation membrane. It represents the pressure when the pressure is gradually increased and the water vapor separation membrane ruptures.

The water vapor separation membrane contains a hydrophilic resin as described above. That is, the water vapor separation membrane preferably contains not only the hydrophilic resin but also other resins as resins constituting the water vapor separation membrane. The other resin is preferably a main component of the resin constituting the water vapor separation membrane. Here, the term "main component" refers to a content of 95% by mass or more relative to the resin contained in the water vapor separation membrane. In this case, the content of the hydrophilic resin is 5% by mass or less. The content of the hydrophilic resin is higher than 0% by mass, and the hydrophilic resin should be contained to such an extent that the desired water permeability is exhibited.

The other resin, that is, the resin that is the main component is not particularly limited, and examples thereof include resins that are used as resins that constitute water vapor separation membranes. Examples of the main component resin include acrylic resin, polyvinyl chloride, polyacrylonitrile, polystyrene, polyamide, polyacetal, polycarbonate, polyphenylene ether, polyphenylene sulfide, polyethylene terephthalate, polytetrafluoroethylene, polyvinylidene fluoride, and polyetherimide. , polyamideimide, polychloroethylene, polyethylene, polypropylene, nylon, crystalline cellulose, polysulfone, polyphenylsulfone, polyethersulfone, ABS (acrylonitrile butadiene styrene) resin, and AS (acrylonitrile styrene) resin. Among these, amorphous polymers such as ABS resin, polyethersulfone, polysulfone, polyvinyl chloride, and polyetherimide are preferred, and polysulfone is more preferred, from the viewpoint of excellent pore size controllability. Moreover, these resins may be used alone, or two or more of them may be used as the main component resin.

The hydrophilic resin is not particularly limited, and specific examples thereof include resins having a hydrophilic group in the molecule. Examples of the hydrophilic resin include cellulose ester; ethylene-vinyl alcohol copolymer; polyvinyl alcohol; pyrrolidone-based resins; and polyacrylic acid esters. Among the resins exemplified above, vinylpyrrolidone-based resins are preferable from the viewpoint of high hydrophilicity and excellent moisture adsorption performance. Among these, polyvinylpyrrolidone is preferable from the viewpoint of being excellent in handleability and cost. Moreover, as the hydrophilic resin, the above-exemplified resins may be used alone, or two or more of them may be used in combination.

Moreover, the manufacturing method of the water vapor separation membrane according to the present embodiment is not particularly limited as long as the above water vapor separation membrane can be manufactured. Examples of this manufacturing method include the following manufacturing methods. The production method includes a step of preparing a membrane-forming stock solution containing a resin constituting the water vapor separation membrane and a solvent (preparation step), a step of forming the membrane-forming stock solution into a hollow fiber shape (formation step), A step of passing the membrane-forming stock solution formed in the form of hollow fibers through a humidified space (passing step), and a step of contacting the membrane-forming stock solution that has passed through the humidified space with an external coagulation solution (contacting step). and the like.

According to such a manufacturing method, first, in the preparation step, a film-forming stock solution containing a resin and a solvent that constitute the water vapor separation membrane is prepared, and in the formation step, the film-forming solution obtained in the preparation step is prepared. The stock solution is formed into hollow fibers. After that, in the passing step, when the membrane-forming undiluted solution formed in the shape of hollow fibers is passed through the humidified space, the membrane-forming undiluted solution formed in the shape of hollow fibers is brought into contact with moisture present in the humidified space. . When the membrane-forming undiluted solution formed in the form of hollow fibers is passed through the humidified space, the membrane-forming undiluted solution formed in the form of hollow fibers is brought into contact with water existing in the humidified space. As a result, phase separation occurs from the outer peripheral surface side of the membrane-forming stock solution formed in the form of hollow fibers, relatively large pores are formed near the outer peripheral surface side, and relatively small pores are formed inside the pores to solidify. is considered to be On the other hand, since only the moisture present in the humidified space comes into contact with the membrane-forming undiluted solution formed in the form of hollow fibers, it is thought that the amount of contact is small and the inner peripheral surface does not solidify. It is considered that this forms the area from the outer peripheral surface to the vicinity of the first region. That is, the average diameter of the holes on the outer peripheral surface is larger than the average diameter of the holes on the inner peripheral surface, and the holes are formed that are larger than the average diameter of the holes on the first region, and further, the inner side near the outer peripheral surface is formed. It is considered that a water vapor separation membrane having the first region is formed in the . After that, in the contacting step, when the membrane-forming undiluted solution that has passed through the humidified space is brought into contact with the external coagulating liquid, phase separation occurs in the region that did not solidify in the phase separation in the passing step, and the inner circumference It is believed that the surface is solidified. At that time, it is believed that solidification is performed so that a relatively large hole is formed inside the first region, a relatively small hole is formed inside the first region, and a smaller hole is formed on the inner peripheral surface. . It is considered that this forms the first region to the inner peripheral surface. That is, inside the first region, a second region larger than the average diameter of the holes in the inner peripheral surface and larger than the average diameter of the holes in the first region is formed, and further inside the second region, the outer peripheral surface It is thought that an inner peripheral surface having holes smaller than the average diameter of the holes in is formed. Therefore, it is considered possible to manufacture the water vapor separation membrane according to the present embodiment, that is, a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency.

The preparation step is not particularly limited as long as it can prepare a membrane-forming stock solution containing a resin and a solvent that constitute the water vapor separation membrane. Specific examples of the preparation process include a method of heating and stirring raw materials for the membrane-forming stock solution. Moreover, kneading is preferable at the time of heating and stirring. The method of heating and stirring is not particularly limited, and for example, twin-screw kneading equipment, a kneader, a mixer, a tank, or the like can be used during kneading.

As described above, the resin preferably contains a hydrophilic resin, and contains not only a hydrophilic resin but also other resins.

As the hydrophilic resin, the resins exemplified as the hydrophilic resin contained in the water vapor separation membrane can be used. Further, as the other resin, the resins exemplified as other resins contained in the water vapor separation membrane can be used.

The solvent is not particularly limited as long as it can dissolve the thermoplastic resin at least at a specific temperature. Examples of the solvent include γ-butyrolactone, ε-caprolactone, dimethylformamide, dimethylsulfoxide, dimethylacetamide, methanol, acetone, glycerin, N-methylpyrrolidone, butyl sebacate, dimethyl phthalate, dibutyl phthalate, and dibutyl phthalate. benzyl, nonylbenzyl phthalate, octyl phthalate, tetrahydrofuran, hexyl benzoate, caprolactone and the like. Among these, dimethylacetamide, N-methylpyrrolidone, and the like are preferable from the viewpoint of high solubility in resins and high solubility in water. As the solvent, the solvents exemplified above may be used alone, or two or more of them may be used in combination.

The membrane-forming stock solution may contain the resin and the solvent, or may consist of these. In addition, the membrane-forming stock solution may contain other components in addition to these components. Other components include, for example, phase separation promoters and additives.

The membrane-forming stock solution obtained in the preparation step is used for producing a water vapor separation membrane. At that time, it is preferable that the obtained membrane-forming stock solution is sufficiently degassed. Then, after weighing with a metering pump such as a gear pump, it is used for manufacturing a water vapor separation membrane, which will be described later.

The formation step is not particularly limited as long as the membrane-forming stock solution can be formed into hollow fibers. Examples of the forming step include an extrusion step of extruding the membrane-forming undiluted solution in the form of hollow fibers. Examples of the extruding step include a step of extruding the membrane-forming undiluted solution from a hollow fiber molding nozzle shown in FIG. FIG. 6 is a schematic diagram showing an example of a hollow fiber molding nozzle used in the manufacturing method according to this embodiment. Further, FIG. 6(a) shows a cross-sectional view thereof, and FIG. 5(b) is a plan view showing the discharge port side of the hollow fiber molding nozzle for discharging the membrane-forming undiluted solution. Specifically, the hollow fiber molding nozzle 21 here includes an annular outer discharge port 26 and a circular or annular inner discharge port 27 disposed inside the outer discharge port 26 . The hollow fiber molding nozzle 21 is provided at the end of a flow tube 24 for circulating the membrane-forming stock solution, and the membrane-forming stock solution flowing in the flow pipe 24 is discharged outward through a flow path 22 in the nozzle. It is discharged from outlet 26 . The hollow fiber molding nozzle 21 discharges the undiluted membrane-forming liquid from the outer discharge port 26, and at the same time, circulates the internal coagulating liquid through the flow pipe 25 and discharges the inner coagulating liquid through the flow path 23 in the nozzle. It is discharged from the outlet 27 . By doing so, the hollow fiber-shaped membrane-forming undiluted solution extruded from the hollow fiber molding nozzle 21 is brought into contact with the internal coagulating solution.

The internal coagulation liquid is not particularly limited as long as it is an internal coagulation liquid capable of producing the water vapor separation membrane. Examples of the internal coagulation liquid include a mixed solvent of dimethylacetamide and glycerin, a mixed solvent of γ-butyrolactone and glycerin, a mixed solvent of γ-butyrolactone and ethylene glycol, a mixed solvent of γ-butyrolactone and water, dimethyl Examples include a mixed solvent of acetamide and water, a mixed solvent of dimethylacetamide and ethylene glycol, a mixed solvent of dimethylformamide and water, and water. Among these, a mixed solvent of dimethylformamide and water and water are preferable from the viewpoint that suitable performance can be obtained.

The passing step is a step of passing the membrane-forming undiluted solution, which has been formed into hollow fibers in the forming step, through a humidified space. By doing so, as described above, phase separation occurs from the outer peripheral surface side of the membrane-forming stock solution formed in the shape of hollow fibers, relatively large pores are formed near the outer peripheral surface side, and relatively small pores are formed inside the pores. It is believed to solidify such that pores are formed. On the other hand, since only the moisture present in the humidified space comes into contact with the membrane-forming undiluted solution formed in the form of hollow fibers, it is thought that the amount of contact is small and the inner peripheral surface does not solidify. It is considered that this forms the area from the outer peripheral surface to the vicinity of the first region. That is, the average diameter of the holes on the outer peripheral surface is larger than the average diameter of the holes on the inner peripheral surface, and the holes are formed that are larger than the average diameter of the holes on the first region, and further, the inner side near the outer peripheral surface is formed. It is considered that a water vapor separation membrane having the first region is formed in the .

The temperature of the space is preferably 20°C or higher and lower than 80°C, more preferably 20 to 70°C, and even more preferably 30 to 70°C. Also, the relative humidity of the space is preferably 30 to 100% RH, preferably 40 to 100% RH, and preferably 50 to 100% RH. If the temperature is too low or the relative humidity is too low, the water vapor transmission performance tends to decrease. It is considered that this is because the phase separation is not properly performed, and the outer peripheral surface and the first coarse layer are not properly formed. Further, when the temperature is too high or the relative humidity is too high, there is a tendency that the strength of the water vapor separation membrane is lowered, or the hollow fiber membrane cannot be suitably formed. Therefore, when the temperature and relative humidity of the space are within the above ranges, it is possible to more preferably produce a water vapor separation membrane with high gas barrier properties and water permeability and high purge efficiency. It is considered that this is because the phase separation in the passing step is performed more favorably.

The time for passing through the space is preferably 0.2 seconds or more and less than 20 seconds, more preferably 0.2 seconds or more and less than 15 seconds, and further preferably 0.2 seconds or more and less than 13 seconds. preferable. If the time is too short, the water vapor permeation performance tends to decrease. It is considered that this is because the phase separation is not properly performed, and the outer peripheral surface and the first coarse layer are not properly formed. On the other hand, if the time is too long, the strength of the water vapor separation membrane tends to be lowered, or the hollow fiber membrane cannot be suitably formed. Therefore, when the time is within the above range, a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency can be more preferably produced. It is considered that this is because the phase separation in the passing step is performed more favorably.

The contacting step is not particularly limited as long as it is a step of contacting the membrane-forming undiluted solution that has passed through the humidified space in the passing step with an external coagulating liquid. Specifically, the contacting step includes a step of immersing the membrane-forming undiluted solution that has passed through the humidified space in the passing step in an external coagulating liquid stored in an external coagulating bath. As described above, it is believed that this step causes phase separation in the region that was not solidified by phase separation in the passing step, and solidifies up to the inner peripheral surface. At that time, it is believed that solidification is performed so that a relatively large hole is formed inside the first region, a relatively small hole is formed inside the first region, and a smaller hole is formed on the inner peripheral surface. . It is considered that this forms the first region to the inner peripheral surface. That is, inside the first region, a second region larger than the average diameter of the holes in the inner peripheral surface and larger than the average diameter of the holes in the first region is formed, and further inside the second region, the outer peripheral surface It is thought that an inner peripheral surface having holes smaller than the average diameter of the holes in is formed. Therefore, it is considered possible to manufacture the water vapor separation membrane according to the present embodiment, that is, a water vapor separation membrane having high gas barrier properties, high water permeability, and high purge efficiency.

The external coagulating liquid is not particularly limited as long as it is a solvent capable of further coagulating the membrane-forming liquid that has passed through the humidified space in the passing step. Specific examples of the external coagulation liquid include water, an aqueous solution containing salts or a solvent, and the like. Examples of salts here include various salts such as sulfates, chlorides, nitrates, and acetates. Water is preferable as the external coagulation liquid.

The temperature of the external coagulating liquid is not particularly limited as long as it is a temperature at which the membrane-forming stock liquid that has passed through the humidified space in the passing step can be further coagulated. Specifically, the temperature of the external coagulation liquid is preferably 20°C or higher and lower than 95°C, more preferably 30°C or higher and lower than 95°C, and further preferably 40°C or higher and lower than 95°C. preferable. If the temperature is too low, the water permeability tends to decrease. It is considered that this is because the solvent exchange rate in the contacting step is slowed down, and the obtained water vapor separation membrane is excessively densified. On the other hand, if the temperature is too high, the gas barrier properties tend to deteriorate. This is believed to be due to the faster solvent exchange rate in the contacting step.

The manufacturing method may include the preparing step, the forming step, the passing step, and the contacting step, and may further include other steps. Examples of the other steps include a step of washing the obtained water vapor separation membrane after the contacting step (washing step), and a step of cross-linking the hydrophilic resin contained in the water vapor separation membrane (cross-linking step). .

The washing step is not particularly limited as long as the obtained water vapor separation membrane can be washed. Examples of the washing method in the washing step include a method of immersing the obtained water vapor separation membrane in a water bath and washing in the water bath. By such washing, the solvent contained in the resulting water vapor separation membrane can be removed. Further, by this washing, the hydrophilic resin contained in the water vapor separation membrane is sequentially removed from the outer peripheral surface side. Since the water vapor separation membrane has the first dense layer, the hydrophilic resin is removed from the first coarse layer, while the second coarse layer inside the first dense layer is removed. It becomes difficult to remove the hydrophilic resin from the layer and the separation layer. Therefore, the remaining amount of the hydrophilic resin can be changed between the outer peripheral surface side and the inner peripheral surface side.

The cross-linking step is not particularly limited as long as the hydrophilic resin contained in the water vapor separation membrane can be cross-linked. The cross-linking step includes, for example, a step of immersing the water vapor separation membrane (the water vapor separation membrane before crosslinking) in an aqueous solution containing a radical initiator, a step of immersing the water vapor separation membrane in a strong acid or a strong alkali, and a heat treatment of the water vapor separation membrane. and a step of subjecting the water vapor separation membrane to radiation treatment.

The water vapor separation membrane according to this embodiment may be crimped. The crimped shape refers to a structure in which the water vapor separation membrane is crimped as if permed. By crimping (applying crimps), even if the packing rate is increased during the module, it is excellent in that the purge efficiency does not decrease.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the scope of the present invention is not limited to these.

[Example 1]
First, as a resin, polysulfone (hereinafter sometimes abbreviated as PSF) (Ultrason S3010 manufactured by BASF Japan Ltd.), as a solvent, dimethylacetamide (DMAc manufactured by Mitsubishi Chemical Corporation), and as a hydrophilic resin, A mixture was prepared with polyvinylpyrrolidone (PVP: Sokalan K-90P manufactured by BASF Japan Ltd.) at a mass ratio of 20:70:10. This mixture was melted in a melting tank under a constant temperature of 95°C. By doing so, a membrane-forming stock solution was obtained.

The membrane-forming stock solution was kneaded and then extruded through a nozzle having a double ring structure (nozzle for forming a hollow fiber membrane) as shown in FIG. At this time, water as an internal coagulating liquid was discharged simultaneously with the membrane-forming stock solution.

The membrane-forming stock solution extruded together with this internal coagulation solution was passed through the humidified space so that the passage time was 6.4 seconds. The moving distance of the membrane-forming stock solution in this humidified space was 80 cm. The humidified space had a temperature of 45° C. and a relative humidity of 100% RH. After that, the membrane-forming undiluted solution that passed through the humidified space was immersed in water having a water temperature of 40° C., which was an external coagulating liquid. By doing so, the membrane-forming stock solution was solidified to obtain a hollow fiber membrane.

The obtained water vapor separation membrane was then washed in water. By doing so, the solvent was removed by extraction and the hydrophilic resin was also partially removed.

The water vapor separation membrane thus obtained had an outer diameter of 780 μm, an inner diameter of 400 μm, and a thickness of 190 μm.

(structure)
By observing the cross section of the water vapor separation membrane according to Example 1 (the surface perpendicular to the longitudinal direction of the water vapor separation membrane) using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.), The membrane structure of the water vapor separation membrane was confirmed. As a result, it was confirmed that the relationship between the pore sizes in the membrane was as shown in FIG. That is, in the membrane structure of the water vapor separation membrane according to Example 1, the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane is smaller than the average diameter of the pores on the outer peripheral surface and smaller than the average diameter of the pores on the outer peripheral surface. a first region in which holes having diameters are formed; It was confirmed that the structure has a second region in which pores with a large average diameter are formed.

(Average diameter of pores on the outer peripheral surface)
An image of the outer peripheral surface of the water vapor separation membrane taken with a scanning electron microscope at a magnification of 5000 (for example, FIG. 3) is binarized using image measurement software (Image-Pro Plus manufactured by Planetron Co., Ltd.). , to obtain the distribution of the pore area. From the obtained area, the diameter when the pores are considered to be a perfect circle is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average diameter of the pores on the outer peripheral surface of the water vapor separation membrane (the above The maximum value in the first coarse layer: outer peripheral surface hole diameter).

(Average diameter of pores in the first region)
The image of the first dense layer in the cross section of the water vapor separation membrane (the plane perpendicular to the longitudinal direction of the water vapor membrane) was taken with a scanning electron microscope at a magnification of 5000 times, and the image measurement software (manufactured by Planetron Co., Ltd.) Image-Pro Plus) was used to obtain the pore area distribution. From the obtained area, the diameter when the pores are considered to be perfect circles is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average of the pores in the first region 13 of the water vapor separation membrane. It was taken as the diameter (the minimum value in the first dense layer). Then, the average value is calculated at a plurality of locations in the thickness direction of the first dense layer observed in the same cross section, and the minimum value is the minimum value in the first dense layer (average of holes in the first region diameter).

(Average diameter of pores in the second region)
The image of the second coarse layer in the cross section of the water vapor separation membrane (the plane perpendicular to the longitudinal direction of the water vapor membrane) was taken with a scanning electron microscope at a magnification of 5000 times. Image-Pro Plus) was used to obtain the pore area distribution. From the obtained area, the diameter when the pores are regarded as perfect circles is calculated, and the mode when the pore distribution is fitted to the normal distribution is the average of the pores in the second region 14 of the water vapor separation membrane. The diameter (the maximum value in the second coarse layer). Then, at a plurality of locations in the film thickness direction in the second coarse layer observed in the same cross section, the average value is calculated, and the maximum value is the maximum value in the second coarse layer (average of holes in the second region diameter).

(Average diameter of holes on the inner peripheral surface)
A membrane module was prepared by using 30 water vapor separation membranes with an effective membrane length of 20 cm. Using this membrane module, a liquid in which dextran was dispersed was allowed to permeate, and the rejection rate was measured. As the dextran, dextran-40 and dextran-70 manufactured by Tokyo Kasei Kogyo Co., Ltd. were used, and the molecular weight of the dextran when the rejection rate by the water vapor separation membrane was 90% was determined. From the obtained molecular weight, the Stokes diameter is calculated using the following Stokes formula, and this Stokes diameter is the average diameter of the pores in the inner peripheral surface (inner peripheral surface pore diameter), that is, in the second dense layer (separation layer) The above minimum value is used.

The Stokes formula is the following formula.

Rs=2KT/(6πηD)
In the above formula, Rs represents the Stokes diameter. K indicates the Boltzmann coefficient and is 1.381×10 ⁻²³ . In addition, K is 298 ° C., which is the absolute temperature, η indicates the viscosity of the solvent, which is 0.00089 Pa s, and D = 8.76 × 10 ^-9 × (Mw: weight average molecular weight) ^{-0 .48} .

(permeation flux of water)
The permeation flux (water permeability) of water at a transmembrane pressure difference of 0.1 MPa of the water vapor separation membrane was measured by measuring the amount of filtrate per unit time in the following operation using the water vapor separation membrane. It was calculated from the obtained amount and the film area.

A membrane filtration device was produced using this water vapor separation membrane. The membrane module loaded in the membrane filtration device has an effective membrane length of 20 cm, 20 hollow fibers, and the lower end is sealed with an epoxy resin. The hollow portion of the water vapor separation membrane is open at the upper end, and the hollow portion of the water vapor separation membrane is sealed with epoxy resin at the lower end. This membrane filtration device filtered pure water from the inner peripheral surface side of the water vapor separation membrane, and obtained filtered water from the outer peripheral surface side of the upper end portion. At this time, the transmembrane pressure difference was adjusted to 0.1 MPa.

The water permeation amount obtained by this measurement method, that is, the permeation flux of water at a transmembrane pressure difference of 0.1 MPa was 15.3 LMH/bar.

(Air leak amount)
After completely drying the water vapor separation membrane using the membrane filtration device, an air pressure of 0.5 MPa is applied from the inner peripheral surface side of the water vapor separation membrane, and the air leaking out from the water vapor separation membrane. was measured. From this measured amount of air, permeation flux (L/m ² /h/bar: LMH/bar) is converted into permeation amount per unit membrane area, unit time, unit pressure, and 1 bar (0.1 MPa) got The obtained permeation flux was taken as the air leak amount. This air leak amount was 3.1 LMH/bar.

(Pressure strength: Bursting strength)
Pressure was applied so as to gradually increase the pressure applied to the inner peripheral surface side of the water vapor separation membrane in the membrane module, and the pressure when the water vapor separation membrane ruptured was measured. The obtained pressure was defined as pressure resistance (bursting strength). The burst strength was 1.4 MPa.

(Absorption intensity of peak derived from hydrophilic resin in infrared absorption spectrum: IR absorption intensity)
An infrared spectrophotometer (JIR-5500 manufactured by JEOL Ltd.) was used to measure infrared absorption spectra of the inner and outer peripheral surfaces of the water vapor separation membrane. The absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum was measured as the absorption intensity at 1671 cm ⁻¹ . As a result, the absorption intensity on the inner peripheral surface side was 0.18, and the absorption intensity on the inner peripheral surface side was 0.03. From this, it was found that more hydrophilic resin was present on the inner peripheral surface side than on the outer peripheral surface side.

(Water vapor permeation rate)
The water vapor permeation rate of the water vapor separation membrane is obtained by measuring the permeation amount of water vapor per unit time in the following operation using the water vapor separation membrane, and calculating the obtained permeation amount, membrane area, and time. Calculated.

A membrane filtration device was produced using this water vapor separation membrane. The membrane module loaded in the membrane filtration device has an effective membrane length of 20 cm, 20 hollow fibers, and the lower end is sealed with an epoxy resin. The hollow portion of the water vapor separation membrane is open at the upper end, and the hollow portion of the water vapor separation membrane is sealed with epoxy resin at the lower end. In this membrane filtration device, air with a relative humidity of 100% RH is continuously supplied from the inner peripheral surface side of the water vapor separation membrane at 1 L / min, and the outer peripheral surface side is reduced to a reduced pressure of 30 kPa, and the inner peripheral surface of the water vapor separation membrane. Water vapor permeating from the side to the outer peripheral side was obtained in a cooling trap. The water vapor permeation rate (mg/min/m) was calculated from the permeation amount of water vapor, the membrane area, and the time.

The water vapor transmission rate obtained by this measurement method was 12.1 mg/min/m.

Production conditions, results, etc. are shown in Table 1.

[Example 2]
The passage time for passing the membrane-forming undiluted solution extruded together with the internal coagulation liquid through the humidified space was changed from 6.4 seconds to 1.6 seconds, and the temperature of the humidified space was changed from 45°C to 35°C. A hollow fiber membrane was obtained in the same manner as in Example 1, except that the external coagulation liquid was changed from water with a water temperature of 40°C to water with a water temperature of 60°C. The moving distance of the membrane-forming stock solution in this humidified space was 20 cm.

Further, the membrane structure of the water vapor separation membrane according to Example 2 was confirmed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). The results are shown in FIGS. 1-3. FIG. 1 is a diagram showing a scanning electron micrograph of a cross section of a water vapor separation membrane according to Example 2. FIG. FIG. 2 is a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the water vapor separation membrane according to Example 2. FIG. 3 is a view showing a scanning electron micrograph of the outer peripheral surface of the water vapor separation membrane according to Example 2. FIG.

In the membrane structure of the water vapor separation membrane according to Example 2, the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane is smaller than the average diameter of the pores on the outer peripheral surface, and the average diameter is smaller than the average diameter of the pores on the outer peripheral surface. a first region in which holes are formed; It was confirmed that the structure has a second region in which a hole having a diameter is formed.

Moreover, various measurements were performed in the same manner as in Example 1.

Production conditions, results, etc. are shown in Table 1.

[Example 3]
A hollow fiber membrane was obtained in the same manner as in Example 1, except that the relative humidity of the humidified space was changed from 100% to 70%.

The membrane structure of the water vapor separation membrane according to Example 3 was confirmed in the same manner as in Example 1. As a result, in the membrane structure of the water vapor separation membrane according to Example 3, the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane was smaller than the average diameter of the pores on the outer peripheral surface, and smaller than the average diameter of the pores on the outer peripheral surface. a first region in which holes having an average diameter are formed; and an inner peripheral surface side of the first region, which is larger than the average diameter of the holes in the inner peripheral surface and the average diameter of the holes in the first region. and a second region in which pores with a larger average diameter are formed.

Moreover, various measurements were performed in the same manner as in Example 1.

Production conditions, results, etc. are shown in Table 1.

[Example 4]
A hollow fiber membrane was obtained in the same manner as in Example 1, except that the relative humidity of the humidified space was changed from 100% to 50%.

The membrane structure of the water vapor separation membrane according to Example 4 was confirmed in the same manner as in Example 1. As a result, in the membrane structure of the water vapor separation membrane according to Example 4, the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane was smaller than the average diameter of the pores on the outer peripheral surface, and smaller than the average diameter of the pores on the outer peripheral surface. a first region in which holes having an average diameter are formed; and an inner peripheral surface side of the first region, which is larger than the average diameter of the holes in the inner peripheral surface and the average diameter of the holes in the first region. and a second region in which pores with a larger average diameter are formed.

Moreover, various measurements were performed in the same manner as in Example 1.

Production conditions, results, etc. are shown in Table 1.

[Comparative example]
It was produced in the same manner as in Example 1, except that instead of passing through a humidified space, it was passed through a dry space. The dry space had a temperature of 45° C. and a relative humidity of 20% RH.

The membrane structure of the water vapor separation membrane according to the comparative example was confirmed using a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.). The results are shown in FIGS. 7-9. FIG. 7 is a diagram showing a scanning electron micrograph of a cross section of a water vapor separation membrane according to a comparative example. FIG. 8 is a scanning electron micrograph of the vicinity of the outer peripheral surface in the cross section of the water vapor separation membrane according to the comparative example. FIG. 9 is a scanning electron micrograph of the outer peripheral surface of a water vapor separation membrane according to a comparative example.

From these electron micrographs, it was found that neither the first dense layer nor the first coarse layer was formed.

Production conditions, results, etc. are shown in Table 1.

From Table 1, it can be seen that the porous hollow fiber water vapor separation membrane containing a hydrophilic resin, the average diameter of the pores on the inner peripheral surface of the water vapor separation membrane being smaller than the average diameter of the pores on the outer peripheral surface of the water vapor separation membrane. , a first region in which holes having an average diameter smaller than the average diameter of the holes in the outer peripheral surface are formed; In addition, if the water vapor separation membrane has a second region in which pores having an average diameter larger than the average diameter of the pores in the first region are formed (Examples 1 to 4), otherwise (Comparative Example) The water vapor permeation rate was very high compared to Further, when comparing Example 1 and Comparative Example, the water vapor separation membrane according to Example 1 has the same level of water permeability and gas barrier properties as compared with the water vapor separation membrane according to Comparative Example, but the water vapor permeation It was fast.

REFERENCE SIGNS LIST 10 water vapor separation membrane 11 inner peripheral surface 12 outer peripheral surface 13 first region 14 second region 21 hollow fiber molding nozzle

Claims (6)

A porous hollow fiber water vapor separation membrane containing a hydrophilic resin,
The average diameter of the pores on the inner peripheral surface of the water vapor separation membrane is smaller than the average diameter of the pores on the outer peripheral surface of the water vapor separation membrane,
a first region in which holes having an average diameter smaller than the average diameter of the holes in the outer peripheral surface are formed;
A second region in which holes having an average diameter larger than the average diameter of the holes in the inner peripheral surface and larger than the average diameter of the holes in the first region are formed on the inner peripheral surface side of the first region. and
A water vapor separation membrane , wherein the average diameter of pores in the outer peripheral surface is 0.1 to 20 μm . The water vapor separation membrane according to claim 1 , wherein the hydrophilic resin is a vinylpyrrolidone resin. 3. The water vapor separation membrane according to claim 1, wherein the absorption intensity of the peak derived from the hydrophilic resin in the infrared absorption spectrum of the inner peripheral surface is stronger than the absorption intensity of the outer peripheral surface. The water vapor separation membrane according to any one of claims 1 to 3 , which has an air permeation flux of 0 LMH/bar or more and less than 5000 LMH/bar. A method for producing a water vapor separation membrane according to any one of claims 1 to 4 ,
a step of preparing a membrane-forming stock solution containing a resin constituting the water vapor separation membrane and a solvent;
A step of forming the membrane-forming stock solution into a hollow fiber shape;
a passing step of passing the membrane-forming undiluted solution formed in the shape of hollow fibers through a humidified space;
a step of contacting the membrane-forming undiluted solution that has passed through the humidified space with an external coagulating solution ;
The method for producing a water vapor separation membrane, wherein the humidified space has a temperature of 20° C. or more and less than 80° C. and a relative humidity of 30 to 100% RH . 6. The method for producing a water vapor separation membrane according to claim 5 , wherein in the passing step, the time for passing through the space is 0.2 seconds or more and less than 20 seconds.

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