JP2012011354A - Forward osmosis membrane, seawater treatment apparatus using forward osmosis membrane, and seawater treatment method using forward osmosis membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forward osmosis membrane in which a permeation flow rate is high, and which is excellent also in strength.SOLUTION: The forward osmosis membrane includes a semipermeable membrane having the thickness of at most 1 μm, and a support which is in contact with the semipermeable membrane, wherein in a part into which a liquid of a membrane surface of the semipermeable membrane can permeate, at least 99% of the membrane surface of the semipermeable membrane is in a not adhering status with the support when observed by right projection.

Description

  The present invention relates to a forward osmosis membrane used in a forward osmosis method. Furthermore, the present invention relates to a seawater treatment apparatus and a seawater treatment method using a forward osmosis membrane.

  Water shortages are a serious problem in dry and densely populated areas around the world. Thus, there is a need for seawater treatment technology that removes salt from seawater.

As a seawater treatment technique, a membrane treatment method is known, and a semipermeable membrane is usually used in the membrane treatment method. The semipermeable membrane is known as a membrane that allows only molecules and ions having a specific size or less to permeate. For example, the semipermeable membrane is a membrane that allows water in seawater to permeate but does not permeate salt. When two kinds of solutions having different solute concentrations are brought into contact with each other across the semipermeable membrane, an osmotic pressure difference is generated between the two solutions, and the solvent of the solution having the lower solute concentration, that is, the lower osmotic pressure side, is It penetrates to the higher solute concentration side, that is, the higher osmotic pressure side. This osmosis phenomenon theoretically continues until the osmotic pressure difference becomes zero. For example, when seawater and water are brought into contact with each other across a semipermeable membrane, the water permeates into the seawater and tries to form an equilibrium state.
As membrane treatment methods using such a semipermeable membrane, a reverse osmosis method (RO method) and a forward osmosis method (FO method) are known.

  The RO method is a technique in which low molecular components such as water are permeated in reverse from a high osmotic pressure side to a low osmotic pressure side. In order to cause such reverse osmosis, in the RO method, a high pressure exceeding the osmotic pressure difference between the two solutions is applied to the side where the osmotic pressure is high. For example, when separating water from seawater, seawater and water are brought into contact with each other across a semipermeable membrane, and the seawater side is subjected to a pressure exceeding the osmotic pressure difference, usually far above the osmotic pressure difference. Apply and allow water in seawater to permeate into the water side.

On the other hand, as disclosed in Patent Document 1 and Patent Document 2, the FO method artificially creates an osmotic pressure difference between two types of solutions using a draw solution having a high osmotic pressure. This is a method of causing the solvent to move. Specifically, a feed solution (feed solution) that is a raw material solution and a draw solution having an osmotic pressure higher than that of the feed solution are brought into contact with each other across a semipermeable membrane. If it does so, the solvent of a feed solution osmose | permeates the draw solution side by the osmotic pressure difference of both solutions. Thereafter, the solvent of the feed solution is collected by volatilizing and collecting the solute components in the draw solution. Conversely, a concentrated feed solution may be collected.
Below, an example in the case of isolate | separating water from seawater is demonstrated according to FIG.
FIG. 1 shows an example of a seawater treatment apparatus using the FO method, where solid arrows indicate the flow of water 11 separated from seawater or seawater, and dotted lines indicate the draw solution or the solute 12 of the draw solution. Each flow is shown. First, the seawater 11 and the draw solution 12 come into contact with each other through the semipermeable membrane 13. Water in the seawater 11 permeates the draw solution 12 side through the semipermeable membrane 13. Then, in the distillation tower 14, the solute component of the draw solution is volatilized from the draw solution diluted with seawater water, thereby separating the water 16 and the solute component 15 of the draw solution. The solute component 15 of the draw solution is gasified by obtaining the gas absorber 17, and then dissolved in the diluted draw solution and reused as the draw solution 12. Reference numeral 18 denotes a pressure gauge.

Thus, the RO method and the FO method are common in that a semipermeable membrane is used, but their mechanisms are completely different. Therefore, the functions required for the reverse osmosis membrane (RO membrane) used in the RO method and the forward osmosis membrane (FO membrane) used in the FO method are also greatly different.
As for the semipermeable membrane portion, the thinner the film thickness, the higher the water permeation rate. In order to achieve a practical permeation rate, the thickness of the semipermeable membrane is 1 μm or less in both cases. Here, since the semipermeable membrane is extremely thin, it is necessary to hold the semipermeable membrane by the support.
In this RO method, in the RO method, a high pressure far exceeding the osmotic pressure difference is applied to cause reverse osmosis, so it is necessary to give the semipermeable membrane a high pressure resistance by applying the support. Therefore, the support is required to have a very small pore diameter and a large film thickness like a laminated structure of a microfiltration membrane and a nonwoven fabric.
On the other hand, in the FO method, the concentration gradient in the vicinity of the semipermeable membrane is an important point because the concentration difference of the solution becomes the driving force for permeation. FIG. 2 is a schematic view showing a general configuration of the FO membrane, in which 21 is a feed solution side, 22 is a draw solution side, 23 is a semipermeable membrane, and 24 is a support. Moreover, the arrow has shown the flow of the solvent of feed solution. In FIG. 2, the support 24 is provided on the draw solution side 22, but may be provided on the feed solution side 21 or on both sides. Here, when the same material as the RO membrane is used for the support 24, the diffusion of the solute component is greatly reduced in the support. This diffusion delay causes a further decrease in solute concentration in the support. This phenomenon is called concentration polarization, and as a result, the osmotic pressure difference between the feed solution and the draw solution is greatly reduced, and the water permeation flow rate is also reduced. For example, when seawater is treated with a draw solution containing carbon dioxide and ammonia, the concentration of sodium ions and chloride ions derived from the salt increases in the vicinity of the semipermeable membrane on the seawater side, and the semipermeable membrane on the draw solution side In the vicinity, particularly in the support, the concentration of carbon dioxide-derived carbonate ions and ammonia-derived ammonium ions is reduced, the osmotic pressure difference is reduced, and water in seawater is less likely to penetrate the semipermeable membrane.
Therefore, on both sides of the semipermeable membrane, there is a need for an FO membrane that suppresses such concentration polarization and has the required strength.

  As described above, since the RO and FO methods have different permeation mechanisms, the performance required for the RO membrane and the FO membrane is completely different. In particular, the RO membrane does not have a problem of concentration polarization in the vicinity of the semipermeable membrane such as the FO membrane because the liquid after permeation does not affect the permeation flow rate. On the other hand, since the FO membrane does not apply mechanical pressure, the strength that can withstand high pressure unlike the RO membrane is not required.

  Here, as an FO film used in the FO method, Patent Document 3 describes that a semipermeable membrane is reinforced by coating and forming the semipermeable membrane on nanofibers. Moreover, although it is not the technique regarding FO film | membrane, the patent document 4 has known the technique which adhere | attaches a porous film | membrane and a support body partially.

  Here, various studies have been made on the RO method, but the FO method has hardly been studied so far. However, in recent years, environmental issues have come to be regarded as important, and the FO method is being demanded from the viewpoint of energy reuse. That is, in the FO method, the energy is substantially only the thermal energy used in the distillation stage for separating the draw solution described above, and compared with the RO method in which the pressure is applied to promote the penetration, Uses little electrical energy. Therefore, the energy used in the FO method can be expected to utilize waste energy, and further development of the FO method is desired.

US Pat. No. 6,391,205 US Patent Application Publication No. 2005/0145568 International Publication WO2008 / 137082 Pamphlet Japanese Patent Laid-Open No. 10-66847

As described above, further technical progress is required for the FO method. Here, when this inventor examined about FO film | membrane of the said patent document 3, it turned out that permeation | transmission flow velocity is not enough. This was thought to be because the permeation flow rate was lowered as a result of trying to improve the strength of the FO film.
The present invention is intended to solve such problems, and an object thereof is to provide an FO membrane having a high permeation flow rate and excellent strength.

Under such circumstances, the inventor of the present application examined the above-mentioned Patent Document 3. In Patent Document 3, since the semipermeable membrane is coated on the nanofiber to form a film, the projection is observed. It was considered that a substantially 100% region of the nanofiber as the support was adhered to the semipermeable membrane.
Here, when the semipermeable membrane used for the FO membrane is supported by the support, it has been considered essential to adhere the semipermeable membrane to the support. However, as a result of examination by the present inventor, it has been found that this very common-sense technique is caused by a decrease in permeation flow rate. This is based on the fact that the semipermeable membrane in the FO membrane is very thin. That is, for example, in the filtration membrane as in Patent Document 4, since the thickness of the filtration membrane can be increased, even if the filtration membrane and the support are adhered, the liquid can freely flow through the filtration membrane, The liquid flow rate does not decrease so much. On the other hand, in the FO membrane, since the semipermeable membrane is required to be thin, when the semipermeable membrane and the support are bonded, the flow of the liquid in the semipermeable membrane is remarkably inhibited, resulting in the permeation flow rate. It was found that it has a great influence on On the other hand, it was naturally predicted that the strength of the obtained FO film was inferior when the ratio of the adhesion area between the semipermeable membrane and the support was reduced.
Under such circumstances, the inventor of the present application has intensively studied, and surprisingly, when the semipermeable membrane is supported by the support, in the portion where the liquid permeates, it can be substantially non-adhered. It was found that the strength required for the FO film can be obtained. That is, the present invention is characterized in that when the semipermeable membrane is supported by the support, the portion where the liquid permeates is substantially non-adhered.
Specifically, the present invention has been achieved by the following means.

(1) A portion having a semipermeable membrane having a thickness of 1 μm or less and a support in contact with the semipermeable membrane, and a portion where the liquid on the membrane surface of the semipermeable membrane can permeate is observed by orthogonal projection. A forward osmosis membrane characterized in that 99% or more of the membrane surface of the semipermeable membrane is in a non-adhesive state with the support.
(2) The support according to (1), wherein the support contains at least one selected from natural polymers, synthetic polymers, metals, glass, ceramics, carbon fibers, and composites thereof. Forward osmosis membrane.
(3) The forward osmosis membrane according to (1) or (2), wherein the support is resistant to a solution containing any one or more of ammonium carbonate, ammonia, carbonic acid, and amines.
(4) The forward osmosis membrane according to any one of (1) to (3), wherein the support is a mesh.
(5) The forward osmosis membrane according to (4), wherein the pore diameter of 80% or more of the pores of the support is distributed within ± 10 μm of the average pore diameter.
(6) The forward osmosis membrane according to any one of (1) to (5), wherein the support has pores having a pore diameter of 500 μm or less.
(7) The forward osmosis membrane according to any one of (1) to (6), wherein the porosity of the support is 0.05 or more.
(8) The forward osmosis membrane according to any one of (1) to (7), wherein the support is provided on both sides of the semipermeable membrane.
(9) A forward osmosis device having the forward osmosis membrane according to any one of (1) to (8).
(10) The forward osmosis device according to (9), which is used for seawater treatment.
(11) A seawater treatment method using the forward osmosis membrane according to any one of (1) to (8).

  According to the present invention, it is possible to provide an FO membrane having excellent strength and excellent permeation flow rate.

FIG. 1 is a schematic diagram showing a conventional technique when seawater is processed using the FO method. FIG. 2 is a schematic view showing a case where a FO method is performed using a conventional FO film.

  Hereinafter, the contents of the present invention will be described in detail. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

  The FO membrane of the present invention has a semipermeable membrane having a thickness of 1 μm or less and a support in contact with the semipermeable membrane, and the portion of the membrane surface of the semipermeable membrane through which liquid can permeate is It is characterized in that 99% or more of the film surface of the semipermeable membrane is in a non-adhered state with the support when observed by orthographic projection. Thus, the permeation | transmission flow rate can be improved, maintaining the intensity | strength required for a FO film | membrane by making the part which can permeate | transmit the liquid of a semipermeable membrane contact a support body in a substantially non-adhesion state.

Here, the semipermeable membrane in the present invention refers to a membrane that allows only molecules, ions, and hydrates of ions not larger than a certain size to pass through and does not allow large molecules to pass through. For example, when it is desired to pass only a solvent such as water from a solution such as seawater, such as when removing salt from seawater, a membrane that passes only the solvent and does not pass a solute such as an ion hydrate derived from salt is used. Say.
The thickness of the semipermeable membrane used in the present invention is 1 μm or less, preferably 500 nm or less, and more preferably 400 nm or less. The lower limit is not particularly defined, but can be, for example, 10 nm or more. In the present invention, the strength required for the FO film can be maintained while increasing the concentration gradient by using such a thin semipermeable membrane.
The density of the semipermeable membrane used in the present invention is preferably a ^{1.0g / cm 3 ~2.5g / cm 3} , more preferably ^{1.1g / cm 3 ~1.8g / cm 3} .
The material of the semipermeable membrane is not particularly defined, but examples thereof include regenerated cellulose, cellulose ester, polyacrylonitrile, Teflon (registered trademark), polyester polymer alloy, polyamide, polyimide, polysulfone, cellulose ester, polyamide, Polyimide is preferable, and cellulose ester, aromatic polyamide, and aromatic polyimide are more preferable.
As the cellulose, cellulose acetate is preferable, and the substitution degree of the hydroxyl group of the cellulose acetate to the acetyl group is preferably 2.0 to 3.0.

In the present invention, the support is in contact with the semipermeable membrane. Here, the support works to increase the membrane breaking strength (pressure resistance) of the semipermeable membrane.
In the present invention, the portion of the semipermeable membrane through which the liquid can permeate is not bonded to the support in 99% or more of the membrane surface of the semipermeable membrane when observed by orthographic projection. . The portion of the semipermeable membrane through which the liquid can permeate refers to a portion in which the liquid can permeate in a normal state when the semipermeable membrane is installed so as to separate two types of liquids having different osmotic pressures. That is, a portion where the semipermeable membrane is covered with a holder or the like that holds the semipermeable membrane does not correspond to a portion where the liquid of the semipermeable membrane can permeate. On the contrary, the portion other than the portion where the penetration of the liquid is completely inhibited corresponds to the portion where the liquid can penetrate even if the liquid does not actually penetrate.
The orthogonal projection refers to a trajectory of a perpendicular foot that drops the FO film on a plane perpendicular to the film surface. Therefore, when the support is constructed by folding a plurality of yarns, fibers, etc., if the overlapping part is bonded to any of the overlapping threads, the part is in an adhesive state. Suppose there is. Further, in the present invention, 99% or more of the membrane surface of the semipermeable membrane where the liquid of the semipermeable membrane can permeate is in a non-adhered state with the support, preferably 99.5% or more. And more preferably 100% non-adhered state.
Here, the non-adhered state means that a portion where the semipermeable membrane and the support are in contact with each other is not fixed. Specifically, it means that the semipermeable membrane and the support are not intentionally attached with an adhesive or the like. On the other hand, those in which the semipermeable membrane and the support are naturally bonded by intermolecular force, static electricity, adsorption via water, or the like are not included in the fixation in the present invention.
In this way, by supporting the semipermeable membrane in a non-adhered state, it is possible to suppress a decrease in permeation flux and to suppress a decrease in permeation flow rate due to the support. In particular, the present invention is extremely significant in that sufficient strength can be maintained and concentration polarization can be suppressed even in reinforcement in a non-adhered state.

The support in the present invention may be provided on one side of the semipermeable membrane, but is preferably provided on both sides of the semipermeable membrane. By setting it as such a structure, the effect of this invention can be exhibited more effectively.
The support in the present invention preferably has pores having a pore diameter of 1000 μm or less, more preferably 700 μm or less, and even more preferably 500 μm or less. The lower limit is not particularly defined, but can be, for example, 10 μm or more. Here, the hole may have various shapes such as a circle, an ellipse, and a square. When the support is a mesh, the pore diameter refers to the diameter of an area formed by four mesh threads, and commercially available products are usually described in catalogs and the like. Moreover, the hole diameter in the case of pseudo-circles, such as an ellipse, says the diameter at the time of converting into a circle. In the present invention, the pore diameters for 80% or more of the pores are preferably distributed within ± 10 μm of the average pore diameter, and more preferably within ± 5 μm. Such a uniform pore diameter can be easily achieved by using a mesh as the support.

Further, the porosity of the support in the present invention is preferably 0.05 or more, more preferably 0.2 or more, and further preferably 0.5 or more. By setting the porosity to 0.05 or more, the mass transfer resistance in the support can be reduced, and the permeation flow rate can be improved. The upper limit value is not particularly defined, but can be set to 0.9 or less, for example.
The porosity (ε) in the present invention refers to the ratio of the volume of the gap contained therein to the total volume in the support.

  The material of the support is not particularly defined as long as it does not depart from the gist of the present invention, but at least selected from natural polymers, synthetic polymers, metals, glass fibers, ceramics, carbon fibers, and composites thereof. One type is exemplified. Examples of natural polymers include cellulose, and synthetic polymers include polyethylene, polypropylene, polyethylene terephthalate (PET), nylon (registered trademark), polytetrafluoroethylene, polyvinylidene fluoride, polysulfone, polyethersulfone, and the like. Examples of the metal include zinc, copper, iron, stainless steel (SUS), and aluminum. In the present invention, in consideration of processing suitability, cost, and the like, a synthetic polymer is preferable, and PET is more preferable.

The support used in the present invention preferably has resistance to a solution containing at least one of ammonium carbonate, ammonia, carbonic acid and amines. The FO film of the present invention is used in the FO method, and the draw solution used in the FO method usually contains one or more of ammonium carbonate, ammonia, carbonic acid, and amines. Therefore, having resistance to the components of such a draw solution is preferable from the viewpoint of improving the durability of the apparatus.
Here, having resistance means that the weight change rate is 20% or less when the support is immersed in these solutions at 25 ° C. for one day.

The shape of the support used in the present invention is not particularly defined as long as it does not depart from the gist of the present invention, and examples thereof include non-woven fabrics, meshes (woven fabrics), punching metals, etc., and uniform pore diameter, porosity, In consideration of processing suitability, cost, etc., a mesh (woven fabric) is preferable. Since the mesh constitutes the flow path of the solvent, there is also an advantage that the permeation becomes smoother.
The average opening diameter of the support is 10 μm to 1000 μm, preferably 10 μm to 400 μm, and more preferably 20 μm to 100 μm.
By setting the average opening diameter to 10 μm or more, it is possible to more effectively suppress a decrease in the permeation flux due to concentration polarization, and by setting the average opening diameter to 1000 μm or less, the destruction of the semipermeable membrane can be more effectively prevented. be able to.
The average aperture diameter can be measured as a DIAMETER having a value of 50% in the CUMLATIVE FILTER FLOW VS DIAMETER graph using an optical microscope or a porometer.

The basis weight of the nonwoven fabric and woven fabric is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably ^{1g / m 2 ~1kg / m 2} , is 10g / m ² ~500g / m ² more ^{preferably, 10g / m 2 ~100g / m} 2 is particularly preferred.
By setting it to 1 g / m ² or more, the strength tends to be improved as a support, and by setting it to 1 kg / m ² or less, the specific gravity of the fiber becomes low as a layer having openings, and the permeation flux due to concentration polarization is reduced. It is possible to suppress the decrease more effectively.

  In the present invention, since the support is not bonded to the semipermeable membrane, the semipermeable membrane layer may move slightly on the support during use. Therefore, it is desirable that the portion constituting the support has a smooth surface with no protrusions and a small friction.

  The thickness (t) of the support in the present invention is preferably 1 μm ≦ t ≦ 500 μm, more preferably 10 μm ≦ t ≦ 300 μm, and further preferably 50 μm ≦ t ≦ 200 μm. By setting the film thickness to 500 μm or less, the mass transfer resistance in the support can be reduced, and by setting it to 1 μm or more, the strength can be improved.

  In the present invention, a known method can be adopted as a method for bringing the support into contact with the semipermeable membrane. For example, there is a method in which a semipermeable membrane is formed in advance on a base material via a sacrificial layer, the sacrificial layer is dissolved in a liquid, the base material is separated, and contacted with a support. In addition, a semipermeable membrane is formed in advance on a base material via a sacrificial layer, and the sacrificial layer and the adhesive component can be dissolved after the semipermeable membrane and the support are brought into contact with each other using an adhesive component. It is also possible to dissolve the sacrificial layer and the adhesive component in solution.

  In a processing apparatus using the FO membrane of the present invention, a plurality of distillation columns are generally used to separate a solute and a solvent in a solution. The treatment apparatus in the present invention can be used for separation of salt and water from seawater or semi-brine water, purification of waste water, purification of contaminated water, osmotic heat engine (OHE) and the like. It can also be used for concentrating fruit juice and vegetable juice.

  In addition to the above, the present invention includes techniques described in US Pat. No. 6,391,205, US Patent Application Publication No. 2005/0145568, and International Publication No. WO 2007/146094 without departing from the present invention. Can be adopted.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Comparative Example 1)
Preparation of semipermeable membrane 1 On a polyethylene terephthalate (PET) sheet, a 6% polyvinyl alcohol (PVA) solution was applied to a dry film thickness of about 2 μm and dried at 100 ° C. A solution obtained by dissolving cellulose acetate (substitution degree: about 2.15) in acetone: cyclohexane = 1: 1 mixed solvent at a weight concentration of 1.65% on the PVA surface of the obtained sheet has a dry film thickness of 0.35 μm. It was applied and dried at 100 ° C. This was immersed in ion-exchanged water at 70 ° C. for 5 minutes to dissolve PVA, whereby the PET sheet and the cellulose acetate film were peeled off to obtain a semipermeable membrane 1.

Example 1
A semi-permeable membrane in ion-exchanged water using a mesh (heat-fusible polyester, manufactured by Dio Kasei Co., Ltd., Diomesh 50-70PTNW, thread diameter: 70 μm, pore diameter: 430 μm, porosity: 0.74) as a support. The FO membrane was obtained by scrubbing 1 with a mesh and bringing it into contact with the support.

(Example 2)
In Example 1, the support was replaced with a mesh (heat-fusible polyester, manufactured by Dio Kasei Co., Ltd., Diomesh 70-55PTNW, thread diameter: 55 μm, hole diameter: 310 μm, porosity: 0.72), In the same manner, an FO film was obtained.

(Example 3)
In Example 1, the support was replaced with a mesh (PET, manufactured by KUBALA, thread diameter: 42 μm, hole diameter: 105 μm, porosity: 0.52), and the rest was carried out in the same manner to obtain an FO membrane. .

Example 4
In Example 1, the support was replaced with a mesh (PET, manufactured by KUBAA Co., Ltd., thread diameter: 48 μm, pore diameter: 79 μm, porosity: 0.39). .

(Example 5)
In Example 1, the support was replaced with a mesh (PET, manufactured by KUBALA, thread diameter: 34 μm, hole diameter: 45 μm, porosity: 0.29), and the rest was carried out in the same manner to obtain an FO membrane. .

(Example 6)
In Example 1, the support was replaced with a mesh (PET, manufactured by KUBALA, thread diameter: 38 μm, pore diameter: 11 μm, porosity: 0.05), and the rest was carried out in the same manner to obtain an FO membrane. .

(Example 7)
In Example 1, the support was replaced with a non-woven fabric (made of Unitika fiber, melty (non-woven fabric having a wire diameter of 14 μm (70%), 20 μm (30%), with a basis weight of 18 g / m ² )), and the others were performed in the same manner. Thus, an FO film was obtained.

(Example 8)
In Example 3, the semi-permeable membrane 1 was scooped with a support mesh (PET, manufactured by KUBAA, thread diameter: 42 μm, pore diameter: 105 μm, porosity: 0.52), and then the same support mesh. Was placed on a surface not supported by a semipermeable membrane mesh to obtain an FO membrane.

Example 9
In Example 1, the support was replaced with a mesh (PET, manufactured by KUBALA, thread diameter: 320 μm, pore diameter: 1000 μm, porosity: 0.58). .

(Comparative Example 2)
Reinforcing by Support Bonding Polyethylene alcohol (PVA) 6% solution was applied on a polyethylene terephthalate (PET) sheet so that the dry film thickness was about 2 μm and dried at 100 ° C. A solution obtained by dissolving cellulose acetate (substitution degree: 52%) in a mixed solvent of acetone: cyclohexane = 1: 1 at a weight concentration of 1.65% on the PVA surface of the obtained sheet so that the dry film thickness becomes 0.35 μm. And dried at 100 ° C. A non-woven fabric made of heat-fusible polyester (non-woven fabric made of unitika fiber melty (wire diameter: 14 μm (70%), 20 μm (30%)) having a basis weight of 18 g / m ² ) is used as an adhesive support. The support was bonded by heat fusion (130 ° C.). This was immersed in ion-exchanged water at 70 ° C. for 5 minutes to dissolve PVA, whereby the PET sheet and the cellulose acetate film were peeled off to obtain an FO film. The adhesion area ratio between the support and the semipermeable membrane was 51% when observed by orthographic projection according to the following method.

(Measurement of adhesion area)
The membrane surface was observed from the semipermeable membrane side with an optical microscope, and the adhesion area ratio was calculated from the ratio of the adhesion area portion in the total area.

The following measurements were performed on the obtained FO film.
(Breaking pressure)
For strength measurement, each FO membrane is set in a pressure membrane filtration device cell, pure water is added thereto, and when pressure is applied to the semipermeable membrane side of the FO membrane, the membrane breaks and pure water leaks. The pressure at the time was measured (breaking pressure). Furthermore, the fracture pressure when using FO membranes having respective pore diameters was fitted to the relationship between the pore diameter and the fracture pressure in the bulge method described in (Macromolecules 2007, 40, 1369-1371), and the relationship between the pore diameter and the fracture pressure was Calculated by simulation. A breaking pressure of 0.03 MPa or more is a practical level.
Formula for bulge method P = 28.9 / a
(P: breaking pressure, a: hole diameter)

(Filtration test)
For the filtration test, a cell for cross flow filtration (manufactured by Fujifilm Techno Products) was used, and raw water and a solute solution were allowed to flow in parallel to the membrane surface through the FO membrane. Then, the amount of water transferred from the feed solution (raw water) to the draw solution (solute solution) side by osmotic pressure was measured. The measurement was performed by measuring the amount of weight change. Here, pure water was used as the feed solution, and a 2.5 M NaCl solution was used as the draw solution. Measurements were performed both in the PRO mode with the support side of the FO membrane facing the raw water (the solute is a semi-permeable membrane side, so there is no effect of concentration polarization) and in the FO mode toward the solute solution side (with the effect of concentration polarization). went. A permeation flux of 3 μm / s or more is a practical level.

(Measurement of permeation flux)
The permeation flux was calculated from the amount of water transferred per unit membrane area.

These results are shown in the table below.

In the above table, the unit of the hole diameter / wire diameter is μm, the unit of the breaking pressure is MPa, and the unit of the water permeation flow rate is μm / s in both the PRO mode and the FO mode. K is a mass transfer resistance serving as an index of concentration polarization, and is a value calculated from the following formula (1) when the permeation flux [μm / s] in the FO mode of water is Jw.
Here, A (pure water permeability coefficient [m / Pa · s]) is a value calculated from the following equation (2) when the permeation flux [μm / s] in the water PRO mode is Jw ′. D (solute diffusion coefficient [m ² / s] in the support body) is 1.6 × 10 ⁻⁹ , and k (boundary membrane mass transfer coefficient [m / s]) is 1.27 × 10 ⁻⁵ .
Jw = Aπexp {−Jw (1 / k + K)} (1)
Jw ′ = Aπexp (−Jw / k) (2)
K (= tτ / εD): Mass transfer resistance in the support [s / m]
D: Solute diffusion coefficient in the support [m ² / s]
Jw: Pure water permeation flux [m / s]
A: Pure water permeability coefficient [m / Pa · s]
π: osmotic pressure in the bulk of the solute [Pa]
k: Boundary membrane mass transfer coefficient [m / s]

As apparent from the above results, when the FO membrane of the present invention was used, it was possible to achieve both high permeation flow rate and excellent strength. Especially Examples 3-5 were excellent in the balance of the high permeation | transmission flow velocity and the outstanding intensity | strength.
On the other hand, the FO film of the comparative example is inferior to either the permeation flow rate or the strength.

DESCRIPTION OF SYMBOLS 11 Seawater 12 Draw solution 13 Semipermeable membrane 14 Distillation tower 15 Draw solution volatile component 16 Water 17 Gas absorber 18 Pressure gauge 21 Feed solution 22 Draw solution 23 Semipermeable membrane 24 Support body

Claims (11)

A portion having a semipermeable membrane having a thickness of 1 μm or less and a support in contact with the semipermeable membrane, and a portion where the liquid on the membrane surface of the semipermeable membrane can permeate is observed by orthographic projection. A forward osmosis membrane, wherein 99% or more of the membrane surface of the permeable membrane is in a non-adhesive state with the support. The forward osmosis according to claim 1, wherein the support comprises at least one selected from natural polymers, synthetic polymers, metals, glasses, ceramics, carbon fibers, and composites thereof. film. The forward osmosis membrane according to claim 1 or 2, wherein the support has resistance to a solution containing at least one of ammonium carbonate, ammonia, carbonic acid, and amines. The forward osmosis membrane according to any one of claims 1 to 3, wherein the support is a mesh. The forward osmosis membrane according to claim 4, wherein the pore diameter of 80% or more of the pores of the support is distributed within ± 10 μm of the average pore diameter. The forward osmosis membrane according to any one of claims 1 to 5, wherein the support has pores having a pore diameter of 500 µm or less. The forward osmosis membrane according to any one of claims 1 to 6, wherein the porosity of the support is 0.05 or more. The forward osmosis membrane according to claim 1, wherein the support is provided on both sides of the semipermeable membrane. The forward osmosis apparatus which has a forward osmosis membrane of any one of Claims 1-8. The forward osmosis device according to claim 9, wherein the forward osmosis device is used for seawater treatment. A seawater treatment method using the forward osmosis membrane according to any one of claims 1 to 8.

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