JP7684824B2 - forward osmosis membrane - Google Patents

Description

The present invention relates to a forward osmosis membrane.

Semipermeable membranes are useful for selectively separating specific components from liquid or gas mixtures, and are ideal for use, for example, in producing high-purity water or separating specific solutes from a solution.

Of the two membrane separation methods that use semipermeable membranes, reverse osmosis and forward osmosis, the reverse osmosis membrane is exposed to high pressure, which has traditionally been the mainstream. Therefore, in order to obtain high strength, the mainstream reverse osmosis membrane is a composite semipermeable membrane that is made by laminating in this order a porous support (e.g., nonwoven fabric), a porous polymer layer (e.g., a polysulfone layer), and a layer that actually functions as a semipermeable membrane (also called a skin layer, separation layer, etc.).

In contrast, in forward osmosis, the driving force is the osmotic pressure that occurs between aqueous solutions with different solute concentrations separated by a forward osmosis membrane, and water moves from a low-salt feed solution (e.g. freshwater) to a high-salt draw solution (e.g. seawater). This means that there is no need to apply high pressure or increase membrane strength to overcome the osmotic pressure as in reverse osmosis, and it is expected to have advantages such as excellent energy savings and a simpler osmosis membrane structure.

However, the forward osmosis method has a problem in that the permeation flux is small (for example, Patent Document 1), and when using forward osmosis membranes to treat large amounts of water for agricultural use or water purification, there is a demand for further improvement in the permeation flux from the low salt concentration side to the high salt concentration side.

On the other hand, the present inventor has disclosed a forward osmosis membrane with excellent permeation flow rate, for example, by using a semipermeable membrane having a polyether ketone structure (for example, Patent Document 2). In the examples of Patent Document 2, a varnish containing a polymer having the above-mentioned polyether ketone structure is used as a release film, and a free-standing membrane is obtained by a casting method.

JP 2014-213262 A International Publication No. 2018/79733

According to the inventors' research, forward osmosis membranes with a large water permeation flux from the feed solution, as disclosed in Patent Document 2, tend to have a large amount of back-diffusion of salt from the draw solution. It has also been found that the amount of back-diffusion of salt per unit water permeation flux is not necessarily low. From this perspective, the inventors have developed a forward osmosis membrane that can achieve both high water permeability and high salt rejection. It will be necessary to continue to improve the performance required of such forward osmosis membranes.

In light of the above problems, the inventors conducted research and found that the magnitude of displacement of the membrane structure when saltwater passes through the semipermeable membrane may affect the back diffusion phenomenon of salt. In other words, it was thought that the smaller the displacement of the structure, the more the back diffusion of salt could be suppressed. On the other hand, it was also thought that there was a concern that a rigid structure with little displacement of the structure would reduce water permeability.

As a result of the investigations conducted by the inventors in light of the above viewpoints, it was discovered that by producing a forward osmosis membrane using a semipermeable membrane containing a resin having a specific molecular structure, it is possible to further suppress the back diffusion of salt and obtain a forward osmosis membrane with an excellent balance between the permeation flux of water and the back diffusion of salt, and this led to the completion of the present invention.

That is, the present invention relates to the following [1] to [4].
[1] an aromatic structure;
A protonic acid structure;
and a structure selected from an ether structure (—O—) and a ketone structure (—CO—),
(I) the solubility parameter of the structural unit having a protonic acid group is 24.0 to 26.0;
(II) The solubility parameter of the structural unit having no protonic acid group is 21.0 to 24.0.
A forward osmosis membrane which is a self-supporting membrane comprising a resin (A) having a structural unit represented by the formula:

[2] The forward osmosis membrane according to [1], wherein the resin (A) has a structural unit (1) represented by the following formula (1) and a structural unit (2) represented by the following formula ( ² ), in which, when the total number of substituents of R ¹ to R ⁵ and X ¹ to X ⁵ is 100 mol %, 76 mol % or more of the substituents of X ¹ to X ⁵ and R ¹ to R ⁵ are hydrogen atoms (-H), and when the total number of substituents of R ⁶ to R ¹⁰ is 100 mol %, 76 mol % or more of the substituents of R 6 to R ¹⁰ are hydrogen atoms (-H).
[In formulas (1) and (2),
R ¹ to R ¹⁰ each independently represent H, Cl, F, CF ₃ or C _m H _2m+1 (m is an integer of 1 to 10);
At least one of R ¹ to R ¹⁰ is C _m H _2m+1 (m is an integer of 1 to 10),
Two or more of each of R ¹ to R ¹⁰ may be present in an aromatic ring, and when two or more C _m H _2m+1 are present in one aromatic ring, each C _m H _2m+1 may be the same as or different from each other.
X ¹ to X ⁵ are each independently H, Cl, F, CF ₃ or a protonic acid group;
At least one of X ¹ to X ⁵ is a protonic acid group;
Two or more of each of X ¹ to X ⁵ may be present in an aromatic ring, and when two or more protonic acid groups are present in one aromatic ring, the respective protonic acid groups may be the same or different.
A ¹ to A ⁶ each independently represent a direct bond, --CH ₂ --, --C(CH ₃ ) ₂ --, --C(CF ₃ ) ₂ --, --O-- or --CO--.
i, j, k and l each independently represent 0 or 1.

[3] The forward osmosis membrane according to [1], wherein the resin (A) includes a protonic acid group-containing resin (A1) and a resin (A2) having a molar fraction of protonic acid group-containing structural units different from that of the resin (A1).

[4] The forward osmosis membrane according to [3], which is a laminate having a layer containing the resin (A1) and a layer containing the resin (A2).

The present invention provides a forward osmosis membrane that has an excellent balance between water permeability and salt rejection rate, specifically, a forward osmosis membrane that has high water permeability and high salt rejection rate.

FIG. 1 is a schematic diagram of an apparatus used to evaluate the separation performance of a forward osmosis membrane in the examples.

The present invention will be specifically described below.
[Forward osmosis membrane]
In a preferred embodiment, the forward osmosis membrane of the present invention comprises a semipermeable membrane and a porous substrate disposed on at least one surface of the semipermeable membrane, wherein the semipermeable membrane comprises a resin (A) (hereinafter sometimes simply referred to as resin (A)) that contains an aromatic structure, a protonic acid group-containing structure, and a structure selected from an ether group and a ketone group, and has a solubility parameter in a specific range.

The semipermeable membrane used in the forward osmosis membrane is often obtained as a free-standing membrane, but preferably has the porous substrate on at least one side, regardless of whether it is a free-standing membrane or not. Such a forward osmosis membrane can achieve high water permeability and high salt rejection.

<Semi-permeable membrane>
The semipermeable membrane contains a resin (A) having a protonic acid group-containing structural unit, an aromatic structure, and a structure selected from an ether group and a ketone group, and is characterized in that the solubility parameter of the structural unit contained in the resin (A) is within a specific range.

The above solubility parameters are used as indicators for determining the affinity between a resin and a solvent, and the higher the value, the higher the cohesive energy between molecules. In other words, it can be considered that resins with high parameter values tend to have a dense structure with small parameters.

In the present invention, the range of the solubility parameter value is 24.0 to 26.0 for the structural unit (I) having a protonic acid group. The preferred upper limit is 25.5, and more preferably 25.0.

On the other hand, for (II) structural units without protonic acid groups, it is 21.0 to 24.0. The preferred upper limit is 23.5, more preferably 23.0, and even more preferably 22.5.

The absolute value of the difference between the parameter value of (I) and the parameter value of (II) above is preferably 1.0 or more. In addition, structures having protonic acid groups usually tend to have stronger intermolecular attraction, and therefore tend to have larger solubility parameter values.

The solubility parameter used in the present invention is calculated using the following formula:

In the above formula, δ _tot represents the solubility parameter (the sum of the dispersion force parameter, polarity parameter, and hydrogen bond parameter: unit = [J ^1/2 /cm ^3/2 ] = MP ^a1/2 ), D represents the dispersion force, P represents the polarity, H represents the contribution of hydrogen bonds, E _coh represents the cohesive energy, and V represents the volume occupied by the target molecule.

The above solubility parameters can be determined, for example, for the structural unit to be calculated using computational science software: HSPiP (Hansen's method).

As a more detailed structure of the resin (A) of the present invention, it is preferable that both the structural units having a protonic acid group and the structural units not having a protonic acid group have a repeating unit having a structure having four or more aromatic ring structures in the main chain. The repeating structural unit preferably has 4 to 10 aromatic ring structures, more preferably 4 to 8 aromatic ring structures, even more preferably 4 to 6 aromatic ring structures, and particularly preferably 4 aromatic ring structures.

Preferred examples of such resins (A) are protonic acid group-containing resins having a structural unit with a protonic acid group represented by the structural formula (1) below and a structural unit without a protonic acid group represented by the structural formula (2) below.

Furthermore, in a preferred embodiment, when the total number of the substituents of X1 ^{to X5} and ^R1 to ^R5 in formula (1) is 100 mol %, 76 mol % or more of the substituents of ^X1 to ^X5 and ^R1 to ^R5 are hydrogen atoms (-H). In a preferred embodiment, when the total number of the substituents of ^R6 to ^R10 is 100 mol %, 76 mol % or more of the substituents of ^R6 to ^R10 are hydrogen atoms (-H). Furthermore, in a particularly preferred embodiment, both of the above-mentioned requirements regarding ^R1 to ^R10 are satisfied.

The more preferred ratio of hydrogen atoms (-H) is 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more.

In formulas (1) and (2),
i, j, k and l each independently represent 0 or 1.

R ¹ to R ¹⁰ are each independently H, Cl, F, CF ₃ or C _m H _2m+1 (m is an integer of 1 to 10), and examples of C _m H _2m+1 include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group and a hexyl group.

At least one of R ¹ to R ¹⁰ is C _m H _2m+1 (m is an integer of 1 to 10). Specifically, i, j, k, and l, as well as R ¹ to R ¹⁰ , are selected so that the structural unit (1) and/or the structural unit (2) have at least one group represented by C _m H _2m+1 . That is, when i, j, k, and l are all 1, at least one of R ¹ to R ¹⁰ is C _m H _2m+1 , but when, for example, i=0, j=1, k=0, and l=1, at least one of R ¹ to R ³ , R ⁵ to R ⁸ , and R ¹⁰ is C _m H _2m+1 .

Two or more of each of R ¹ to R ¹⁰ may be present in an aromatic ring, and when two or more C _m H _2m+1 are present in one aromatic ring, each C _m H _2m+1 may be the same as or different from each other.

^X1 to ^X5 are each independently H, Cl, F, _CF3 or a protonic acid group, and at least one of X1 ^{to X5} is a protonic acid group. Specifically, i and j and ^X1 to ^X5 are selected so that the structural unit (1) has at least one protonic acid group. That is, when i=1 and j=1, at least one of ^X1 to ^X5 is a protonic acid group, but when j=0, at least one of ^X1 to ^X3 is a protonic acid group, and when i=0 and j=1, at least one of ^X1 to ^X3 and ^X5 is a protonic acid group.

Two or more of each of X ¹ to X ⁵ may be present in an aromatic ring, and when two or more protonic acid groups are present in one aromatic ring, the respective protonic acid groups may be the same or different.

A ¹ to A ⁶ each independently represent a direct bond, --CH ₂ --, --C(CH ₃ ) ₂ --, --C(CF ₃ ) ₂ --, --O-- or --CO--, and at least one of A ¹ to A ⁶ is preferably --CO--.

The lines at both ends of formulas (1) and (2) indicate bonds between adjacent structural units.

In the present invention, the protonic acid group means a functional group which easily releases a proton or a group in which a hydrogen atom thereof has been substituted with Na or K. Examples of such a functional group include a sulfonic acid group (-SO ₃ H), a carboxylic acid group (-COOH), a phosphonic acid group (-PO ₃ H ₂ ), an alkylsulfonic acid group (-(CH ₂ ) _n SO ₃ H), an alkylcarboxylic acid group (-(CH ₂ ) _n COOH), an alkylphosphonic acid group (-(CH ₂ ) _n PO ₃ H ₂ ), a hydroxyphenyl group (-C ₆ H ₄ OH) and groups in which a terminal hydrogen atom of these groups has been substituted with Na or K. n is an integer of 1 to 10. The protonic acid group is preferably -C _n' H _2n' -SO ₃ Y (n' is an integer of 0 to 10, preferably 0, and Y is H, Na or K).

The molar fraction of protonic acid group-containing structural units is the ratio of the number of protonic acid group-containing structural units to the total number of structural units constituting the resin.

Examples of the structural unit (1) include structural units represented by the following formula (1-1) or (1-2), and in these structures, A ¹ is preferably --CO--.

(In the formula, each Z is independently the protonic acid group, each s is independently an integer of 0 to 3, each t is independently an integer of 0 to 4, and the lines at both ends indicate bonds to adjacent structural units. The definitions of symbols other than these are as described above.)

Examples of the structural unit (2) include structural units represented by the following formula (2-1) or (2-2):

(In the formula, each t is independently an integer of 0 to 4, and the lines at both ends indicate bonds to adjacent structural units. The symbols other than t are defined as above.)

In the present invention, as described above, it is preferable that the number of hydrocarbon groups (C _m H _2m+1 ) in the above formula is small and the number of hydrogen atoms (--H) is large.

In the entire resin (A), the molar fraction of the structural unit (1) relative to the total amount of the structural unit (1) and the structural unit (2) is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.25 or more, since a semipermeable membrane with high water permeability can be formed; and is preferably 0.9 or less, more preferably 0.7 or less, and even more preferably 0.6 or less, since a semipermeable membrane with high salt rejection and no gelation can be formed.

A preferred embodiment of the resin (A) is one that contains at least a protonic acid group-containing resin (A1) and a resin (A2) that has a larger molar fraction of protonic acid group-containing structural units than the resin (A1) (hereinafter, the resins (A), (A1) and (A2) may be simply referred to as "resin (A)", "resin (A1)" and "resin (A2)", respectively).

From the viewpoint of the balance between water permeability and salt rejection rate, the absolute value of the difference between the molar fraction of protonic acid groups contained in the resin (A1) and the molar fraction of protonic acid groups contained in the resin (A2) is preferably 0.03 to 0.6. A more preferred lower limit is 0.06, even more preferred 0.1, and particularly preferred 0.15. On the other hand, a more preferred upper limit is 0.5, even more preferred 0.45, and particularly preferred 0.4.

In addition, in the above-mentioned regulation of the difference in molar fraction, the number of resins contained in resin (A) is not limited to two. When resin (A) contains three or more resins with different molar fractions of structural unit (1), the above-mentioned regulation of the difference in molar fraction of structural unit (1) needs to be satisfied by at least one set of "two resins."

The resin (A) has excellent water permeability. In a more preferred embodiment, at least two resins having different molar fractions of protonic acid group-containing structural units, i.e., the resin (A1) and the resin (A2), are used. The resin (A2) has a large molar fraction of protonic acid group-containing structural units, which improves water permeability, while the resin (A1) has a small molar fraction of protonic acid group-containing structural units, which tends to suppress back diffusion of salt.

By using the forward osmosis membrane (semipermeable membrane) of the present invention, the back diffusion of the salt can be effectively suppressed.

The reason why the forward osmosis membrane (semipermeable membrane) of the present invention exhibits the above-mentioned effects is unclear, but the inventors speculate as follows.

One of the objectives of the present invention is to suppress the back diffusion of salt. It is believed that back diffusion of salt occurs in relatively large gaps or defects that exist in the semipermeable membrane. Before the water penetration phenomenon occurs, such gaps and defects will hardly exist. However, the pressure caused by water penetration or the permeation of water can cause defects like those mentioned above, which is thought to increase the back diffusion of salt.

In the forward osmosis membrane of the present invention, the resin used has a high solubility parameter and is thought to have a relatively high tendency to aggregate due to the polymer chain structure of the resin. For this reason, even if water permeation occurs, gaps and defects such as those described above are unlikely to occur, and as a result, it can be thought that reverse diffusion of salt is suppressed.

It was thought that suppressing the occurrence of defects as described above might lead to a decrease in water permeability, but in the end, the resin structure used in the present invention had little effect on water permeability. It is believed that the reason why the forward osmosis membrane of the present invention exhibits high water permeability is due to another structural factor.

Resin (A) may further contain a structural unit derived from a polyfunctional compound described below. Resin (A) may be crosslinked or non-crosslinked.

The weight average molecular weight (Mw) of resin (A), measured under the following conditions (1) to (6) using GPC (Gel Permeation Chromatography), is preferably 70,000 or more, more preferably 80,000 or more, and even more preferably 90,000 or more. When the molecular weight is within the above range, the resulting semipermeable membrane has high mechanical properties and is less likely to break during membrane formation or use. In addition, the weight average molecular weight is preferably 180,000 or less from the viewpoint of gel generation rate.

(1) Measurement temperature: 40℃
(2) Developing solvent: N,N-dimethylformamide (DMF)
(3) Flow rate: 1.0ml/min
(4) Injection volume: 500μl
(5) Detector: UV detector
(6) Molecular weight standard: standard polystyrene The weight average molecular weight can be controlled by adjusting the molar ratio of raw material monomers and the amount of end-capping agent when producing the resin (A).

The protonic acid group equivalent of resin (A), i.e., the mass of resin (A) per mole of protonic acid group, is preferably 200 g/mol or more, since a semipermeable membrane that is insoluble in water or methanol, suppresses swelling, and has a small amount of electrolyte permeation through the membrane is obtained. In addition, since a semipermeable membrane that has high water permeability and is highly economical is obtained, it is preferably 5000 g/mol or less, more preferably 1000 g/mol or less.

In particular, if both the resin (A1) and the resin (A2) have the structure of formula (1), or the structure of formula (1) and the structure of formula (2), the dispersion of these resins is considered to be good. For this reason, it is considered that a dense, multi-stage continuous layer of pseudo (A1)/(A2) units is formed, so that the water permeability properties and the effect of suppressing reverse diffusion of salts can be efficiently exhibited.

In one embodiment, the semipermeable membrane preferably has a gradient in the concentration of the protonic acid groups derived from the resin (A) in the thickness direction of the semipermeable membrane. The concentration gradient may be such that the concentration increases continuously or in a stepwise manner. One example of such a case is that the semipermeable membrane is a laminated membrane having a layer (L1) containing a resin (A1) and a layer (L2) containing a resin (A2). The thickness ratio of the layer (L1) to the layer (L2) (thickness of L1:thickness of L2) is usually 5:95 to 80:20, preferably 20:80 to 60:40. Such a multilayer structure provides higher water permeability and salt rejection.

This embodiment is preferable in that it allows the effect of the (A1)/(A2) unit configuration to be more clearly expressed.

The concentration gradient of the protonic acid groups derived from resin (A) refers to the change in the concentration of the protonic acid groups contained in resin (A) in the thickness direction of the semipermeable membrane. When the protonic acid groups are sulfonic groups or groups in which the terminal hydrogen atoms are substituted with Na or K, the concentration gradient can be confirmed by analyzing the concentration distribution of sulfur atoms in the cross section of the semipermeable membrane by elemental mapping.

Here, when using a forward osmosis membrane, it is preferable to arrange the forward osmosis membrane so that the side of the semipermeable membrane with a higher protonic acid group concentration faces the feed solution side and the side of the semipermeable membrane with a lower protonic acid group concentration faces the draw solution side. For example, it is preferable to arrange the forward osmosis membrane so that the layer (L2) containing resin (A2) faces the feed solution side and the layer (L1) containing resin (A1) faces the draw solution side. In such an embodiment, higher water permeability and salt rejection rate can be obtained.

In one embodiment, the semipermeable membrane is preferably formed from a mixture containing at least resin (A1) and resin (A2). As an example, the semipermeable membrane has a structure separated into at least two phases corresponding to resin (A1) and resin (A2), respectively. This phase-separated structure provides higher water permeability and salt rejection. In the mixture, the mass ratio (A1:A2) of resin (A1) to resin (A2) is usually 10:90 to 90:10, preferably 30:70 to 70:30.

Such a phase separation structure can be confirmed by observation with an electron microscope (TEM or SEM). Possible phase separation structures include a sea-island structure and an interpenetrating structure, but the interpenetrating structure is more preferable from the viewpoint of preventing back diffusion of salt from the draw solution. In the case of a sea-island structure, it is preferable that the resin (A1) having a small molar fraction of protonic acid group-containing structural units forms the sea phase, and the resin (A2) having a large molar fraction forms the island phase.

In the present invention, a semipermeable membrane can be produced as a free-standing membrane using resin (A) as a raw material, and a forward osmosis membrane with high water permeability and high salt rejection can be obtained by laminating this semipermeable membrane with a porous substrate.

The semipermeable membrane consists essentially of resin (A) but may contain other components in small amounts (e.g., 1% by mass or less, or 0.1% by mass or less) that do not impair the effects of the present invention.

The thickness of the semipermeable membrane is usually 3.0 μm or less, preferably 0.01 to 3.0 μm, and more preferably 0.01 to 1.5 μm. A forward osmosis membrane using a semipermeable membrane with a thickness within this range has sufficient membrane strength and exhibits water permeability that is sufficiently high for practical use. The thickness of the semipermeable membrane can be controlled by the manufacturing conditions of the semipermeable membrane, such as the temperature and pressure during press molding, the varnish concentration and coating thickness during casting, etc.

Here, the structural units (1) in the resins (A1) and (A2) may be the same or different, and the structural units (2) in the resins (A1) and (A2) may be the same or different.

(Method for producing resin (A))
Resin (A) can be obtained by condensation of monomers having an aromatic ring according to a conventionally known method (for example, the method described in WO 2003/33566).

and a monomer having a halogen substituent represented by the following formulae (1b) and (2b):

The resin can be obtained by condensation polymerization with a monomer having a hydroxyl group represented by the following formula:

In the formula, Y is a halogen atom, and the meanings of the other symbols are the same as those of the same symbols used in the above formulas (1) and (2). The halogen atoms are preferably fluorine and chlorine.

It is preferable to use _a basic catalyst such as _K2CO3 for the condensation.

Examples of the monomer represented by the above formula (1a) (wherein at least one of X ¹ and X ² is a protonic acid group) include protonic acid group-containing aromatic dihalide compounds such as 5,5'-carbonylbis(sodium 2-fluorobenzenesulfonate) and 5,5'-carbonylbis(sodium 2-chlorobenzenesulfonate).

Examples of the monomer represented by the above formula (2a) include:
Aromatic dihalide compounds such as 4,4'-difluorobenzophenone, 3,3'-difluorobenzophenone, 4,4'-dichlorobenzophenone, 3,3'-dichlorobenzophenone, 4,4'-difluorobiphenyl, 4,4'-difluorodiphenylmethane, 4,4'-dichlorodiphenylmethane, and 4,4'-difluorodiphenyl ether; and alkyl group-containing aromatic dihalide compounds such as 3,3'-dimethyl-4,4'-difluorobenzophenone, 3,3'-diethyl-4,4'-difluorobenzophenone, 3,3',5,5'-tetramethyl-4,4'-difluorobenzophenone, 3,3'-dimethyl-4,4'-dichlorobenzophenone, and 3,3',4,4'-tetramethyl-5,5'-dichlorobenzophenone.

Examples of the monomer represented by the above formula (2b) (or the monomer represented by the above formula (1b) (wherein X ³ to X ⁵ are all hydrogen atoms)) include
Aromatic dihydroxy compounds such as 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybenzophenone, 2,2-bis(4-hydroxyphenyl)propane, 1,1,1,3,3,3-hexafluoro-2,2-bis(4-hydroxyphenyl)propane, 1,4-bis(4-hydroxyphenyl)benzene, α,α'-bis(4-hydroxyphenyl)-1,4-dimethylbenzene, α,α'-bis(4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(4-hydroxyphenyl)-1,3-diisopropylbenzene, 1,4-bis(4-hydroxybenzoyl)benzene, and 3,3'-difluoro-4,4'-dihydroxybiphenyl; and 3,3'-dimethyl-4,4'-dihydroxybiphenyl, 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl, 3,3'-dimethyl-4,4'-dihydroxydiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylmethane (also known as bis(3,5-dimethyl-4-hydroxyphenyl)methane), 3,3',5,5'-tetraethyl-4,4'-dihydroxydiphenylmethane, 3,3'-dimethyl-4,4'-dihydroxydiphenyl ether, 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenyl ether, 2,2-bis(3-methyl-4-hydroxydiphenyl Examples of alkyl group-containing aromatic dihydroxy compounds include 2,2-bis(3-ethyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, α,α'-bis(3-methyl-4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(3,5-dimethyl-4-hydroxyphenyl)-1,4-diisopropylbenzene, α,α'-bis(3-methyl-4-hydroxyphenyl)-1,3-diisopropylbenzene, and α,α'-bis(3,5-dimethyl-4-hydroxyphenyl)-1,3-diisopropylbenzene.

A polyfunctional compound may be copolymerized with the monomer as long as the solvent solubility of resin (A) is not impaired. By copolymerizing a polyfunctional compound, resin (A) can have a micro-crosslinked structure. Examples of polyfunctional compounds include those having three or more hydroxyl groups in one molecule, such as (2,4-dihydroxyphenyl)(4-hydroxyphenyl)methanone, 4-[1-(4-hydroxyphenyl)-1-methylethyl]-1,3-benzenediol, 4-[(2,3,5-trimethyl-4-hydroxyphenyl)methyl]-1,3-benzenediol, 4-[(4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, (4-hydroxyphenyl)(2,3,4-trihydroxyphenyl)methanone, 4-[(3,5-dimethyl- 4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, 4-[(2,3,5-trimethyl-4-hydroxyphenyl)methyl]-1,2,3-benzenetriol, 4,4'-[1,4-phenylenebis(1-methylethylidene)]bis[benzene-1,2-diol], 5,5'-[1,4-phenylenebis(1-methylethylidene)]bis[benzene-1,2,3-triol], α,α,α'-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene, phloroglucin, pyrogallol, etc.

From the viewpoint of preventing a decrease in the solvent solubility of resin (A), a decrease in the fluidity of the resin during membrane formation, and a decrease in the elongation rate of the semipermeable membrane, the amount of these copolymerizations is preferably 0 to 8 mol%/total OH equivalent (i.e., of the total amount (100 mol%) of OH groups possessed by the monomer of formula (1b), the monomer of formula (2b), and the polyfunctional monomer, 0 to 8 mol% are OH groups derived from the polyfunctional monomer), and more preferably 0 to 5 mol%/total OH equivalent.

Tensile modulus, tensile breaking strength and elongation
The semipermeable membrane has a tensile modulus of elasticity of preferably 0.8 to 2.0 GPa, more preferably 1.2 to 1.6 GPa. The semipermeable membrane has a tensile breaking strength of preferably 40 MPa or more, with an upper limit of, for example, 100 MPa. The semipermeable membrane has an elongation percentage of preferably 40% or more, with an upper limit of, for example, 200%. These tensile modulus of elasticity, tensile breaking strength and elongation percentage are measured under the following conditions.

A test piece with length x width x thickness = 100 mm x 10 mm x 5 μm is prepared and pulled at a speed of 50 mm/min using a tensile testing machine. When the test piece breaks (fractures), the strength (tensile load value divided by the cross-sectional area of the test piece) and the elongation are determined.

The elongation is calculated according to the following formula:
Elongation rate (%) = 100 x (L - L ₀ ) / L ₀
(L ₀ : length of test piece before test L : length of test piece at break)
The tensile modulus of elasticity is determined by dividing the load at break by the cross-sectional area of the test piece and the amount of strain at break, ie, (LL ₀ )/L ₀ .

The tensile strength at break and the elongation can be increased, for example, by increasing the molecular weight of resin (A).

Solubility and mass loss rate
The solubility of the semipermeable membrane in dimethyl sulfoxide (hereinafter also referred to as "DMSO") and water can be evaluated by the following mass loss rate, respectively. The mass loss rate is preferably less than 2 mass%, more preferably 1.0 mass% or less, and particularly preferably 0.5 mass% or less.

The semipermeable membrane is left to stand under a nitrogen atmosphere at 150°C for 4 hours to dry, and then weighed. The semipermeable membrane is immersed in DMSO or water and left to stand at 25°C for 24 hours. The semipermeable membrane is removed from the DMSO or water, left to stand under a nitrogen atmosphere at 150°C for 4 hours to dry, and then weighed. The mass loss rate is calculated from the following formula based on the mass of the semipermeable membrane before and after immersion.

Mass reduction rate=(mass of semipermeable membrane before immersion−mass of semipermeable membrane after immersion)/mass of semipermeable membrane before immersion×100
The amount of dissolution can be reduced, for example, by crosslinking the resin (A), and therefore the amount of dissolution can be kept within the above range even if the protonic acid group equivalent is small.

(Method of manufacturing semipermeable membrane)

In the present invention, the semipermeable membrane can be obtained using known molding methods such as press molding and extrusion molding. Among these, a method of obtaining a membrane by casting a varnish containing the resin is preferred from the viewpoint of ease of producing a thin film. Specifically, the varnish is applied to a film serving as a substrate, and the solvent is removed by volatilization to obtain a semipermeable membrane. Furthermore, the semipermeable membrane can be peeled off from the film to form a free-standing membrane.

(Varnish of Resin (A))
Resin (A) has a molecular structure that is basically linear, and even if it has a crosslinked structure derived from the polyfunctional compound, the amount of the crosslinked structure is small, so that it has excellent solvent solubility. Therefore, resin (A) can be in the form of a varnish dissolved in a solvent.

Examples of organic compounds (S) used as so-called solvents to form varnishes include, but are not limited to, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, and butanol; hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methyl chloride and methylene chloride; ethers such as dichloroethyl ether, 1,4-dioxane, and tetrahydrofuran; fatty acid esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; cellosolves such as 2-methoxyethanol and 2-ethoxyethanol; and aprotic polar solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and dimethyl carbonate. These can be used alone or in combination of two or more. Among these, lower alcohols (methanol, ethanol, 1-propanol, 2-propanol, t-butyl alcohol, etc.), tetrahydrofuran, N,N-dimethylformamide, N-methyl-2-pyrrolidone, etc. are preferred because they are water-soluble, and mixed solvents of these with water are also preferred. The resin concentration in the varnish can be selected depending on the method of using the varnish, but is preferably 1% by mass or more and 80% by mass or less.

(film)
The film (so-called release film) used in the casting method of the present invention is preferably a film having excellent release properties.
Representative examples of the material of the above-mentioned film include glass plates, polyester films such as PET films, and PBT films.Other examples include polyolefin films such as polyethylene films, polypropylene films, and poly-4-methyl-1-pentene films (product name: TPX (registered trademark)), halogen-containing films such as polyvinyl chloride films, polyvinylidene chloride films, and polyvinylidene fluoride films, poly(meth)acrylate-based films such as polyacrylic acid esters and polymethacrylic acid esters, polyamide films such as various nylon films, olefin-based films containing polar groups such as (meth)acrylic acid, (meth)acrylic acid esters, and vinyl acetate, and films containing hydroxyl groups such as polyvinyl alcohol.

Among the above, polyester film and polyamide film are preferred, taking into consideration the ease of drying at high temperatures and costs, and polyester film is particularly preferred.
In addition, the surface shape is preferably as smooth as possible. In addition, the film preferably has a release layer on the surface. As the raw material for the release layer, for example, a known material such as a silicone-based release agent can be used.

If organic solvents used during casting remain in the semipermeable membrane, the mechanical strength of the semipermeable membrane may decrease and the membrane may become more susceptible to breakage. Therefore, it is preferable to thoroughly dry the semipermeable membrane produced by the casting method and/or wash it with water, an aqueous sulfuric acid solution, hydrochloric acid, or the like.

When the protonic acid group of the resin (A) used to manufacture the semipermeable membrane is a functional group that easily releases protons, in which a hydrogen atom has been replaced with Na or K, a membrane of the resin (A) may be formed, and then the membrane may be brought into contact with hydrochloric acid, an aqueous solution of sulfuric acid, or the like, to replace the Na or K of the protonic acid group with a hydrogen atom.

A semipermeable membrane, specifically a laminated membrane, in which the concentration of the protonic acid groups described above has a gradient in the thickness direction of the semipermeable membrane, can be obtained, for example, by forming a layer (L1) containing resin (A1) and then forming a layer (L2) containing resin (A2) on the layer (L1), or by forming a layer (L2) containing resin (A2) and then forming a layer (L1) containing resin (A1) on the layer (L2).

It is desirable that the organic compound (S) contained in the varnish used to form the L2 layer is, of course, a compound in which the L1 layer is insoluble or poorly soluble.

In the lamination process, any of the steps (e.g., the step of forming the first film, the step of forming the second film to form a laminate structure, etc.) may be subjected to light irradiation such as UV or plasma treatment. It is particularly preferable to irradiate the layer containing the resin (A2) with the light.

In addition, the semipermeable membrane formed from a mixture containing at least the above-mentioned resins (A1) and (A2) can adjust the dispersion diameter of the phase separation structure, for example, by the stirring speed of the mixed resin or varnish.

<Porous base material>
From the viewpoint of handling and the like, it is preferable to use the semipermeable membrane of the present invention in combination with a layer of a porous substrate or a mesh material.

The porous substrate preferably has an air permeability of 100 to 400 ^{cm 3} /cm ² /s, which is measured according to Method A (Fragile type method) of JIS L 1096 as follows.

Attach a 20 cm x 20 cm test piece to the testing machine, adjust the suction fan and air holes so that the inclined barometer reads 125 Pa, and measure the pressure indicated by the vertical barometer. Using the measured pressure and the type of air hole, use the conversion table provided with the testing machine to determine the amount of air passing through the test piece.

The thickness of the porous substrate is usually 50 to 700 μm, preferably 80 to 600 μm, and more preferably 100 to 500 μm.

Since a thin porous substrate having such high air permeability is preferably used for the forward osmosis membrane, it is believed that the concentration polarization that occurs inside the porous substrate when the forward osmosis membrane is used is suppressed, and the fluid resistance when water permeates the forward osmosis membrane can be reduced, resulting in high water permeability in the forward osmosis membrane. The air permeability and thickness of the porous substrate can be controlled by conventional methods.

Preferred materials for the porous substrate include synthetic resins and natural fibers.

Synthetic resins include thermoplastic resins and thermosetting resins, with thermoplastic resins being preferred. Specific examples of thermoplastic resins include olefin polymers, polyester resins, polyamide resins, polyvinyl chloride, and (meth)acrylic resins. Among these, olefin polymers and polyester resins are preferred, with olefin polymers being particularly preferred.

Specific examples of olefin polymers include homopolymers or copolymers of α-olefins, or copolymers of α-olefins and other monomers. Examples of α-olefins include α-olefins having 2 to 8 carbon atoms, such as ethylene, propylene, and 1-butene. Olefin polymers include polyolefin resins such as polypropylene, polyethylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-4-methyl-1-pentene copolymers, propylene-1-butene copolymers, and 4-methyl-1-pentene-1-decene copolymers, as well as copolymers of α-olefins and other monomers, such as ethylene-vinyl alcohol copolymers.

Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples of polyamide resins include nylon 6 and nylon 66.

Natural fibers include plant fibers such as cotton and hemp, and animal fibers such as silk and wool. Of these, cotton and silk are preferred.

Examples of the porous substrate include cloth substrates such as woven fabric, nonwoven fabric, and knitted fabric, and foam sheets. Among these, cloth substrates are preferred, woven fabric and nonwoven fabric are more preferred, and nonwoven fabric is particularly preferred.

Examples of nonwoven fabrics include long fiber nonwoven fabrics made by the spunbond method, short fiber nonwoven fabrics made by the meltblown method, long fiber nonwoven fabrics such as flash spun nonwoven fabrics, spunlace nonwoven fabrics, airlaid nonwoven fabrics, thermal bond nonwoven fabrics, needle punch nonwoven fabrics, and chemical bond nonwoven fabrics, with spunbond nonwoven fabrics and meltblown nonwoven fabrics being preferred. Of these, spunbond nonwoven fabrics are preferred, and spunbond nonwoven fabrics of polyethylene terephthalate or polypropylene are particularly preferred.

The nonwoven fabric may be made of composite fibers made of different resins, and may be a core-sheath or side-by-side composite fiber in which a different resin is arranged on the outer surface side of the fiber. Examples of composite fibers include polyethylene/polypropylene core-sheath or side-by-side composite fibers.

The nonwoven fabric may be a laminated nonwoven fabric. Examples of laminated nonwoven fabrics include laminated nonwoven fabrics containing spunbonded nonwoven fabric and meltblown nonwoven fabric, such as a laminated spunbonded nonwoven fabric and a meltblown nonwoven fabric (SM), and a laminated spunbonded nonwoven fabric, meltblown nonwoven fabric, and a laminated spunbonded nonwoven fabric, meltblown nonwoven fabric, and spunbonded nonwoven fabric (SMS).

To obtain such a laminated nonwoven fabric, a spunbond nonwoven fabric and a meltblown nonwoven fabric are laminated together and integrated. Examples of integration methods include a method in which a spunbond nonwoven fabric and a meltblown nonwoven fabric are layered together and heated and pressurized, a method in which the two are bonded together using an adhesive such as a hot melt adhesive or a solvent-based adhesive, and a method in which fibers are deposited on the spunbond nonwoven fabric by the meltblown method and then thermally fused.

The nonwoven fabric may be a laminated nonwoven fabric in which a porous film having micropores is sandwiched between layers of nonwoven fabric. Examples of such laminated nonwoven fabric include a polypropylene (PP) nonwoven fabric, a porous PP film, and a PP nonwoven fabric (SFS) laminated in this order, and a PP nonwoven fabric, a porous PP film, and a rayon PP nonwoven fabric (SFR) laminated in this order.

The nonwoven fabric preferably has a basis weight (in the case of a laminated nonwoven fabric, the basis weight of the laminated nonwoven fabric) of about 10 to 80 g/m ² , and more preferably about 20 to 40 g/m ² .

The forward osmosis membrane of the present invention may have the porous substrate on both sides of the semipermeable membrane. In this embodiment, the strength of the forward osmosis membrane is further improved.

The forward osmosis membrane of the present invention may include a layer other than the porous substrate on both sides or one side of the semipermeable membrane in the order of semipermeable membrane/layer other than the porous substrate/porous substrate, but it is preferable not to include a layer other than the porous substrate in terms of obtaining good permeability. A polyamide layer may be included as a layer other than the porous substrate, but the thickness of the layer is preferably 100 μm or less.

<Method of manufacturing forward osmosis membrane>
The forward osmosis membrane can be produced, for example, by producing the semipermeable membrane as a free-standing membrane and sandwiching the semipermeable membrane between two of the porous substrates from both sides.

Specifically, the forward osmosis membrane can be manufactured by the following procedure. For example, a dilute solution of resin (A) is applied to a substrate such as PET so that the thickness after drying is the desired thickness, and after drying, the formed membrane is peeled off as a free-standing membrane. In one preferred embodiment of the present invention, the light irradiation step or plasma treatment step is provided in the process from this application to the formation of a free-standing membrane. Among these, it is also preferable to perform the light irradiation step after the drying step and before the step of peeling off the free-standing membrane.

The present invention is a method for producing a forward osmosis membrane by attaching one or two porous substrates such as nonwoven fabrics to one or both sides of the freestanding membrane. In addition, the light irradiation process of the present invention may be included in a process for forming a forward osmosis membrane using this porous membrane and the semipermeable membrane, in addition to the membrane formation process.

When the area of the forward osmosis membrane is large, the semipermeable membrane and the porous substrate may be bonded together with an adhesive to maintain the distance between them without affecting permeability.

The forward osmosis membrane can also be produced by producing the semipermeable membrane as a free-standing membrane and laminating it on the porous substrate. In this case, the two may be attached together using an adhesive.

According to the above-mentioned manufacturing method, the semipermeable membrane described above is first manufactured as a free-standing membrane, which is then laminated on a porous substrate (such as a nonwoven fabric) or sandwiched between two porous substrates (such as a nonwoven fabric) to manufacture a forward osmosis membrane. This allows the thickness of the semipermeable membrane to be controlled, and allows the easy manufacture of a forward osmosis membrane that exhibits high water permeability and high salt rejection.

[Uses of forward osmosis membranes]
The forward osmosis membrane element of the present invention includes the forward osmosis membrane and spacer of the present invention described above. In other words, the forward osmosis membrane element of the present invention is a conventional forward osmosis membrane element including a forward osmosis membrane and a spacer, in which the forward osmosis membrane of the present invention is used as the forward osmosis membrane. As the spacer, a conventionally known spacer used in forward osmosis membrane elements can be used.

The forward osmosis membrane module of the present invention comprises a forward osmosis membrane element of the present invention housed in a container. In other words, the forward osmosis membrane module of the present invention is a conventional forward osmosis membrane element in which a forward osmosis membrane element is housed in a container, but the forward osmosis membrane element of the present invention is used as the forward osmosis membrane element. As the container, a conventionally known container used in a forward osmosis membrane module can be used.

The system of the present invention includes a forward osmosis membrane module of the present invention, and a drive pump for passing a feed solution (FS) on one side of the forward osmosis membrane of the present invention provided in the forward osmosis membrane module, and a draw solution (DS) having a higher solute concentration, such as salt, than the feed solution on the other side, and is configured to move water contained in the feed solution to the draw solution through the forward osmosis membrane.

With such an apparatus, pressure can also be applied from the FS side to the DS side. In some embodiments of the present invention, it may be preferable to apply pressure from the FS side to the DS side, for example, it may be preferable to apply a pressure of preferably 15 kPa or less, more preferably 12 kPa or less, and even more preferably 10 kPa or less from the FS side to the DS side.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
The abbreviations used in the present examples and comparative examples are as follows.

(1) Solvent DMSO: dimethyl sulfoxide NMP: N-methyl-2-pyrrolidone DMF: N,N-dimethylformamide

(2) Components of aromatic polyether DFBP: 4,4'-difluorobenzophenone DSDFBP: 5,5'-carbonylbis(sodium 2-fluorobenzenesulfonate)
BPA: 4,4'-(2,2-propanediyl)diphenol TMBPF: 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylmethane

Various measurement methods (methods for calculating solubility parameters)
The solubility parameter of the resin was calculated using the following formula.

In the above formula, δ _tot represents the solubility parameter (the sum of the dispersion force parameter, polarity parameter, and hydrogen bond parameter: unit = [J ^1/2 /cm ^3/2 ] = MP ^a1/2 ), D represents the dispersion force, P represents the polarity, H represents the contribution of hydrogen bonds, E _coh represents the cohesive energy, and V represents the volume occupied by the target molecule.

Using computational science software: HSPiP (Hansen's method), the solubility parameter values (SP values) of the resins of the examples and the resins of the comparative examples were calculated from the structures (U1), (U2), (UC1), and (UC2) described below. The calculation results are shown in Table 2.

(Method of Measuring Film Thickness)
Measurements were performed using a Nikon Digimicro MH-15M type device (contact type film thickness measuring device: minimum reading: 0.01 μm) in the following manner. The results are shown in Table 3.

At the stage where the varnish was applied to the substrate and dried, i.e., at the stage of the "substrate/coating film" laminate, a portion was cut out as a sample for thickness measurement. The thickness was measured using the above-mentioned device (thickness A (μm)). Next, the film at the measurement point was peeled off from the substrate, and the thickness of the substrate at that point was measured (thickness B (μm)).

From the above results, the value was calculated using the formula "Film thickness = Thickness A - Thickness B". Measurements were taken at five or more locations, and the average value was determined as the film thickness. In the case of semipermeable membranes with a laminated structure of two or more layers, the above procedure was repeated for each layer formed (average value of five or more measurement locations). The film thickness of each layer was determined from the difference between the respective measurement values.

(Method of evaluating forward osmosis membrane)
The performance of the forward osmosis membrane was evaluated by the following method using an apparatus 10 as shown in FIG. 1. The apparatus 10 includes a feed solution tank 1, a flow path 2, a pump 3, a draw solution tank 11, a flow path 12, a pump 13, and an evaluation cell 21. The feed solution tank 1 is placed on a balance 4, and the draw solution tank 11 is equipped with an electric conductivity meter 15. At the start of the evaluation, the feed solution tank 1 stores 500 g of Milli-Q water having an electric conductivity of 50 μS/cm or less as a feed solution FS (Feed Solution), and the draw solution tank 11 stores 800 g of a 0.6 M aqueous ammonium sulfate solution as a draw solution DS (Draw Solution). The feed solution in the feed solution tank 1 flows through the flow path 2 at a rate of 0.6 L/min by using the pump 3, and the draw solution in the draw solution tank 11 flows through the flow path 12 at a rate of 0.6 L/min by using the pump 13. The feed solution flowing through flow path 2 and the draw solution flowing through flow path 12 are in contact with each other inside evaluation cell 21 via a forward osmosis membrane 22 having an effective membrane area of 0.0042 ^m2 . Through the forward osmosis membrane 22, a part of the feed solution moves to the draw solution, and a part of the salt (NaCl) in the draw solution moves (backflows) to the feed solution.

<Water permeation flux (Jw)>
The weight loss of the feed solution was measured every minute using the balance 4, and the weight loss per unit time and unit area of the forward osmosis membrane was defined as the water permeation flux (L/( ^m2 ·h)). The results are shown in Table 3.

<Salt Reverse Diffusion Permeability Factor (SRSF)>
The change in electrical conductivity of the draw solution was measured every minute using the electrical conductivity meter 15, and converted into the change in weight of the draw solution. The change in weight per unit time per unit area of the forward osmosis membrane was defined as the salt permeation rate (g/( ^m2 ·h)). This value was further divided by the permeation flux (Jw) to calculate the SRSF value (g/L). The results are shown in Table 3.

(Resin Synthesis Example 1)
In a five-necked reactor equipped with a nitrogen inlet tube, a thermometer, a reflux condenser, and a stirrer, 40.2 g (0.095 mol) of D 2 SDFBP, 62.2 g (0.285 mol) of DFBP, 86.8 g (0.380 mol) of BPA, and 65.7 g (0.475 mol) of potassium carbonate were weighed out. 756.2 g of DMSO and 302.1 g of toluene were added thereto, stirred under a nitrogen atmosphere, heated at 130° C. for 12 hours, and the generated water was removed from the system, and then the toluene was distilled off.

The reaction was continued at 160°C for 12 hours to obtain a viscous polymer solution. The obtained solution was diluted with 570 g of toluene and then poured into 2400 g of methanol. The precipitated polymer powder was filtered, washed, and then dried at 150°C for 4 hours to obtain 160.6 g of polyether ketone powder (resin 1). Resin (1) contains the structural unit (1) as follows:

The structure (U1) represented by the following formula (2) is used as the structural unit (2):

The compound has a structure (U2) represented by the following formula:
The content of the structure (U1) was 25 mol % (wherein the total of the structure (U1) and the structure (U2) is 100 mol %, the same applies below).

(Resin Synthesis Example 2)
The resin raw materials and solvent were 48.1 g (0.114 mol) of DSDFBP, 58.0 g (0.265 mol) of DFBP, 86.8 g (0.380 mol) of BPA, 65.7 g (0.475 mol) of potassium carbonate, and 756.2 g of DMSO and 302.1 g of toluene, and the same procedure as in Example 1 was used to obtain 160.2 g of polymer powder (resin 2). The content of the structure (U1) was 30 mol%.

(Resin Synthesis Example 3)
The resin raw materials and solvent were 64.2 g (0.152 mol) of DSDFBP, 49.8 g (0.228 mol) of DFBP, 86.8 g (0.380 mol) of BPA, and 65.7 g (0.475 mol) of potassium carbonate, as well as 756.2 g of DMSO and 302.1 g of toluene, and the same procedure as in Resin Synthesis Example 1 was used to obtain 159.8 g of polymer powder (Resin 3). The content of the structure (U1) was 40 mol%.

(Resin Synthesis Example 4)
The resin raw materials and solvent were DSDFBP 96.3g (0.228mol), DFBP 33.2g (0.152mol), BPA 86.8g (0.380mol), potassium carbonate 65.7g (0.475mol), DMSO 756.2g, and toluene 302.1g, and the same procedure as in Resin Synthesis Example 1 was used to obtain 160.1g of polymer powder (Resin 4). The content of the structure (U1) was 60 mol%.

(Reference resin synthesis example N5)
The resin raw materials and solvent were 80.2 g (0.190 mol) of DSDFBP, 41.5 g (0.190 mol) of DFBP, 97.4 g (0.380 mol) of TMBPF, 65.7 g (0.475 mol) of potassium carbonate, 876.4 g of DMSO, and 292.1 g of toluene, and the same procedure as in Resin Synthesis Example 1 was repeated to obtain 174.6 g of polymer powder (Resin N5). Resin N5 contains the following structural unit (1):

As the structural unit (2), a structure (UC1) represented by the following formula (2) is used:

The content of the structure (UC1) was 50 mol % (the total of the structure (UC1) and the structure (UC2) is 100 mol %, the same applies below).

(Reference resin synthesis example N6)
The resin raw materials and solvent were DSDFBP 96.3g (0.228mol), DFBP 33.2g (0.152mol), TMBPF 97.4g (0.380mol), potassium carbonate 65.7g (0.475mol), DMSO 907.5g, and toluene 302.5g, and the same procedure as in Resin Synthesis Example 1 was used to obtain 173.6g of polymer powder (Resin N6). The content of the structure (UC1) was 60 mol%.

(Comparative Resin Synthesis Example 1)
The resin raw materials and solvent were 40.1 g (0.095 mol) of DSDFBP, 62.2 g (0.285 mol) of DFBP, 97.4 g (0.380 mol) of TMBPF, and 65.7 g (0.475 mol) of potassium carbonate, as well as 783.4 g of DMSO and 261.1 g of toluene. Except for this, 171.6 g of polymer powder (resin C1) was obtained in the same manner as in Resin Synthesis Example 1. The content of the structure (UC1) was 25 mol%.

(Comparative Resin Synthesis Example 2)
The resin raw materials and solvent were 48.1 g (0.114 mol) of DSDFBP, 58.0 g (0.265 mol) of DFBP, 97.4 g (0.380 mol) of TMBPF, 65.7 g (0.475 mol) of potassium carbonate, and 814.4 g of DMSO and 271.5 g of toluene, but the procedure was the same as in Example 1 to obtain 175.2 g of polymer powder (resin C2). The content of the structure (UC1) was 30 mol%.

(Comparative Resin Synthesis Example 3)
The resin raw materials and solvent were 64.2 g (0.152 mol) of DSDFBP, 49.8 g (0.228 mol) of DFBP, 97.4 g (0.380 mol) of TMBPF, 65.7 g (0.475 mol) of potassium carbonate, and 845.4 g of DMSO and 281.8 g of toluene, and the same procedure as in Resin Synthesis Example 1 was used to obtain 168.7 g of polymer powder (Resin C3). The content of the structure (UC1) was 40 mol%.

The content of structural units (sulfonic acid units) containing sulfonic acid groups in each of the resins synthesized above is shown in Table 1 below. The solubility parameters of each of the resins synthesized above are shown in Table 2 below.

[Example 1]
Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish. This varnish was cast onto a release PET substrate (smooth surface film), dried at 110°C for 3 minutes, and peeled off from the PET substrate to form a free-standing film, thereby obtaining Film 1.

[Example 2]
Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, and this varnish was cast onto the release PET substrate and dried at 110°C for 3 minutes. This was then peeled off from the PET substrate to form a free-standing film, thereby obtaining Film 2.

[Example 3]
Resin 3 produced in Resin Synthesis Example 3 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish. This varnish was cast onto the release PET substrate and dried at 110° C. for 3 minutes. This was then peeled off from the PET substrate to form a free-standing film, thereby obtaining Film 3.

[Preparation of forward osmosis membrane]
Two sheets of polypropylene nonwoven fabric ("Syntex (registered trademark) PS-105" manufactured by Mitsui Chemicals, Inc.) having an air permeability of 300 ^m3 / ^cm2 /s as measured by JIS L 1096 Method A (Fragile type method), and a thickness of 290 μm were prepared, and the membranes 1 to 3 were sandwiched between these nonwoven fabrics and integrated to obtain the forward osmosis membranes of Examples 1 to 3. The evaluation results are shown in Table 3.

[Example 4]
Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110° C. for 3 minutes to obtain a film of Resin 1. Thereafter, Resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin 1 and dried at 160° C. for 3 minutes to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film 4.

[Example 5]
Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110° C. for 3 minutes to obtain a film. Thereafter, Resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin 1 and dried at 160° C. for 3 minutes to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, and film 5 was obtained.

[Example 6]
Resin 1 produced in Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film. Thereafter , Resin 4 produced in Resin Synthesis Example 4 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin 1 and dried for 10 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film 6.

[Example 7]
Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110° C. for 3 minutes to obtain a film of Resin 2. Thereafter, Resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a methyl cellosolve solvent to prepare a varnish, which was then cast onto the film of Resin 2 and dried at 160° C. for 3 minutes to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film 7.

[Example 8]
Resin 2 produced in Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110° C. for 3 minutes to obtain a film. Thereafter, Resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a methyl cellosolve solvent to prepare a varnish, which was then cast onto the film of Resin 3 and dried at 160° C. for 3 minutes to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, and Film 8 was obtained.

[Example 9]
Resin 3 produced in Resin Synthesis Example 3 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film. Thereafter, Resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a methyl cellosolve solvent to prepare a varnish, which was then cast onto the film of Resin 3 and dried for 10 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film 9.

[Example 10]
Resin 3 produced in Resin Synthesis Example 3 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto a PET substrate and dried for 3 minutes at 110° C. to obtain a film. Thereafter, Resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a solvent of DMF and methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin 3 and dried for 10 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining film 10.

[Preparation of forward osmosis membrane]
Two sheets of polyester nonwoven fabric (Hirose Paper Co., Ltd., "05TH-20") were prepared, and the membranes 4 to 10 were sandwiched between these nonwoven fabrics and integrated to obtain the forward osmosis membranes of Examples 4 to 10. The evaluation results are shown in Table 3.

[Comparative Example 1]
Resin C1 produced in Comparative Resin Synthesis Example 1 was dissolved in a solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110°C for 3 minutes. The varnish was then peeled off from the PET substrate to form a free-standing film, thereby obtaining Film C1.

[Comparative Example 2]
Resin C2 produced in Comparative Resin Synthesis Example 2 was dissolved in a solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110°C for 3 minutes. The varnish was then peeled off from the PET substrate to form a free-standing film, thereby obtaining Film C2.

[Comparative Example 3]
Resin C3 produced in Comparative Resin Synthesis Example 3 was dissolved in a solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110°C for 3 minutes. The varnish was then peeled off from the PET substrate to form a free-standing film, thereby obtaining Film C3.

[Comparative Example 4]
Resin C1 produced in Comparative Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film of resin C1. Thereafter, resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of resin C1 and dried for 3 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining film C4.

[Comparative Example 5]
Resin C1 produced in Comparative Resin Synthesis Example 1 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried at 110° C. for 3 minutes to obtain a film of resin C1. Thereafter, resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of resin 1 and dried at 160° C. for 3 minutes to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, and film C5 was obtained.

[Comparative Example 6]
Resin C2 produced in Comparative Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film of Resin C2. Thereafter, Resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin C2 and dried for 3 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film C6.

[Comparative Example 7]
Resin C2 produced in Comparative Resin Synthesis Example 2 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film of resin C2. Thereafter, Resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of resin C2 and dried for 3 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining film C7.

[Comparative Example 8]
Resin C3 produced in Comparative Resin Synthesis Example 3 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film of Resin C3. Thereafter, Resin N5 produced in Reference Resin Synthesis Example 5 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of Resin C3 and dried for 3 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, thereby obtaining Film C8.

[Comparative Example 9]
Resin C3 produced in Comparative Resin Synthesis Example 3 was dissolved in a mixed solvent of DMF and toluene to prepare a varnish, which was then cast onto the release PET substrate and dried for 3 minutes at 110° C. to obtain a film of resin C3. Thereafter, Resin N6 produced in Reference Resin Synthesis Example 6 was dissolved in a solvent of methyl cellosolve to prepare a varnish, which was then cast onto the film of resin C3 and dried for 3 minutes at 160° C. to obtain a two-layer film, which was then peeled off from the PET substrate to obtain a free-standing film, and film C9 was obtained.

[Preparation of forward osmosis membrane]
Two sheets of polyester nonwoven fabric (Hirose Paper Co., Ltd., "05TH-20") were prepared, and the membranes C4 to C9 were sandwiched between these nonwoven fabrics and integrated to obtain the forward osmosis membranes of Comparative Examples 1 to 9. The evaluation results are shown in Table 3.

Reference Signs List 1 Feed solution tank 2, 12 Flow path 3, 13 Pump 4, 14 Balance 10 Evaluation device 11 Draw solution tank 15 Electrical conductivity meter 21 Evaluation cell 22 Forward osmosis membrane DS Draw solution FS Feed solution

Claims (4)

An aromatic structure;
A protonic acid structure;
and a structure selected from an ether structure (—O—) and a ketone structure (—CO—),
(I) the solubility parameter of the structural unit having a protonic acid group is 24.0 to 26.0;
(II) The solubility parameter of the structural unit having no protonic acid group is 21.0 to 24.0.
The resin (A) has a structural unit represented by the formula :
The resin (A) has a structural unit (1) represented by the following formula (1) and a structural unit (2) represented by the following formula (2), in which, when the total number of substituents of R ¹ to R ⁵ and X ¹ to X ⁵ is 100 mol %, 76 mol % or more of the substituents of X ¹ to X ⁵ and R ¹ to R ⁵ are hydrogen atoms (-H), and when the total number of substituents of R ⁶ to R ¹⁰ is 100 mol %, 76 mol % or more of the substituents of R ⁶ to R ¹⁰ are hydrogen atoms (-H), and the forward osmosis membrane is a self-supporting membrane.
[In formulas (1) and (2),
R ¹ to R ¹⁰ each independently represent H, Cl, F, CF ₃ or C _m H _2m+1 (m is an integer of 1 to 10);
At least one of R ¹ to R ¹⁰ is C _m H _2m+1 (m is an integer of 1 to 10),
Two or more of each of R ¹ to R ¹⁰ may be present in an aromatic ring, and when two or more C _m H _2m+1 are present in one aromatic ring, each C _m H _2m+1 may be the same as or different from each other.
X ¹ to X ⁵ are each independently H, Cl, F, CF ₃ or a protonic acid group;
At least one of X ¹ to X ⁵ is a protonic acid group;
Two or more of each of X ¹ to X ⁵ may be present in an aromatic ring, and when two or more protonic acid groups are present in one aromatic ring, the respective protonic acid groups may be the same or different.
A ¹ to A ⁶ each independently represent a direct bond, --CH ₂ --, --C(CH ₃ ) ₂ --, --C(CF ₃ ) ₂ --, --O-- or --CO--, and A ³ and A ⁶ each independently represent --C(CH ₃ ) ₂ -- or --C(CF ₃ ) ₂ --.
i=0, j=1, k=0 and l=1 .] The forward osmosis membrane according to claim 1, wherein the structural unit (1) is a structural unit represented by the following formula (1-1) or (1-2), and the structural unit (2) is a structural unit represented by the following formula (2-1) or (2-2).


(In the above formula, each Z is independently the protonic acid group, each s is independently an integer of 0 to 3, each t is independently an integer of 0 to 4, and the other symbols are as defined in formulas (1) and (2).) 2. The forward osmosis membrane according to claim 1, wherein the resin (A) comprises a protonic acid group-containing resin (A1) and a resin (A2) having a molar fraction of a protonic acid group-containing structural unit different from that of the (A1). The forward osmosis membrane according to claim 3, wherein the forward osmosis membrane is a laminate having a layer containing the resin (A1) and a layer containing the resin (A2).