WO2013172330A1

WO2013172330A1 - Semi-permeable membrane and method for manufacturing same, and concentration-difference power-generating method using semi-permeable membrane

Info

Publication number: WO2013172330A1
Application number: PCT/JP2013/063382
Authority: WO
Inventors: 尊大徳山; 隆一郎平鍋; 洋樹富岡; 栗原　優; 上田　充; 知哉東原; 誉礼相羽
Original assignee: 東レ株式会社; 国立大学法人東京工業大学
Priority date: 2012-05-14
Filing date: 2013-05-14
Publication date: 2013-11-21
Also published as: JP6282585B2; JPWO2013172330A1

Abstract

Provided is a semi-permeable membrane having high permeability which is suitable for concentration-difference power generation with high mechanical strength. The semi-permeable membrane has at least two layers: a dense layer (A) having substantial solute removal capability and a finely porous layer (B). The main component of the dense layer (A) is a polymer having the repeating unit structure shown in (Formula 1). (In this formula, Ar₁, Ar₂, Ar₃ and Ar₄ each have an aromatic ring structure; R₁, R₂, R₃and R₄ are each a hydrogen atom or have structure P, structure P having any structure selected from among an alkyl group, alkylcarboxylic acid or a salt thereof, alkyl sulfonic acid or a salt thereof, and alkyl phosphate or a salt thereof; X is any structure selected from among a carboxylic acid group or salt thereof, a sulfonic acid group or salt thereof, and a phosphate group or salt thereof; and m and n are the constituent ratios (%) of the repeating unit structures; m ≥ 0, n ≥ 0, and m + n = 100 being satisfied, and at least one of R₃and R₄ being structure P when m = 0.)

Description

Semipermeable membrane and method for producing the same, concentration difference power generation method using semipermeable membrane

The present invention relates to a semipermeable membrane suitably used for a power generation method using a concentration difference.

In recent years, an increase in carbon dioxide gas due to consumption of fossil fuels has become a global environmental problem, and search for new decarbonization energy technologies has been actively conducted. As one of them, concentration difference power generation using salt concentration difference energy such as seawater and fresh water is highly expected in that the energy source is inexhaustible and the environmental load is extremely small. As a method for converting the salinity difference into energy, the anti-pressure osmosis method using a semipermeable membrane has attracted attention. In this method, when two liquids with different salinity concentrations are separated by a semipermeable membrane, the turbine generator is driven using the flow from fresh water to salt water caused by the forward osmosis phenomenon. (S. Rob, Journal of Membrane Science, Volume 1, p49 and p249, Elsevier (1976)).

Concentration difference power generation using the anti-pressure osmosis method has been developed so far using commercially available composite semipermeable membranes, etc., but it is sufficient because of the structural problems of the composite semipermeable membrane described below. The amount of power generation could not be obtained. That is, a conventional composite semipermeable membrane usually consists of three layers: a separation functional layer that blocks salt, a support membrane that has a thickness of several tens of μm or more that supports the structure of the separation functional layer, and a base material that supports them. However, since it is difficult to block the salt content 100% in the separation functional layer, a slight amount of permeated salt from the salt water side to the fresh water side stays in the support membrane to cause concentration polarization. There has been a problem that the amount of water permeation, which is the driving force for power generation, is greatly reduced due to the decrease in power. For example, an asymmetric membrane having a structure that supports a separation functional layer on a substrate having a large porosity is formed as a membrane for use in a desalination method using the forward osmosis phenomenon, which is an application similar to the concentration difference power generation. The method (Patent Document 1) further discloses a composite membrane (Patent Document 2) in which a separation functional layer is formed on a substrate having a large porosity.

However, these examples using polyamide membranes and cellulose membranes used as reverse osmosis membranes as the membrane material have a smaller pressure difference before and after the membrane compared to the reverse osmosis system, and water permeability is higher than the removal rate. However, sufficient performance was not obtained in the system of concentration difference power generation, which is regarded as important. Therefore, a new material that has a possibility of developing high water permeability with a small pressure difference has been demanded, and attention has been paid to polybenzimidazole, which has led to the present invention. As a membrane using polybenzimidazole, Patent Document 3 is disclosed as a reverse osmosis membrane.

US Pat. No. 7,445,712 US Patent Application Publication No. 2011/0102680 US Patent Application Publication No. 2011/0266223

Patent Documents

1 and 2 have not led to a fundamental solution to the problem of a decrease in driving force of power generation due to salt retention. Further, the membrane made of polybenzimidazole mentioned in Patent Document 3 also has low water permeability, and it has not been possible to obtain a useful power generation amount in the concentration difference power generation system.

In the reported examples of

Patent Documents

1 and 2, both focus on salt retention in the support layer that supports the separation functional layer, and the salt content suitable for the forward osmosis membrane is obtained by making the support layer structure sparse. Efforts are being made to bring it closer to difficult structures. However, even if the retention of the salt is reduced by making the support layer sparse, even the high mechanical strength, which is the original advantage of the support layer, must be sacrificed at the same time. The separation functional layer in these reports alone has a remarkably low mechanical strength or lacks self-supporting properties, and it is difficult to take out only the separation functional layer.

An object of the present invention is to solve the problems of the prior art and provide a semipermeable membrane suitable for concentration difference power generation having high water permeability and high mechanical strength.

The semipermeable membrane of the present invention is a semipermeable membrane comprising at least two layers of a dense layer A having a substantial solute removing ability and a microporous layer B, and the dense layer A is represented by the following (formula 1): The main component is a polymer having a repeating unit structure shown in FIG.

(In the formula, Ar ₁ , Ar ₂ , Ar ₃ and Ar ₄ are each an arbitrary aromatic ring structure, and R ₁ , R ₂ , R ₃ and R ₄ are each a hydrogen atom or a structure P, and the structure P is An alkyl group, an alkyl carboxylic acid or a salt thereof, an alkyl sulfonic acid or a salt thereof, an alkyl phosphoric acid or a salt thereof, and X is a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof , A phosphoric acid group or a salt thereof, m and n represent the constituent ratio (%) of the repeating unit structure, m ≧ 0, n ≧ 0, m + n = 100 is satisfied, m = When 0, at least one of R ₃ and R ₄ is the structure P.)

Furthermore, the polymer having the repeating unit structure represented by the above (Formula 1) may be crosslinked by a covalent bond with each other via an N atom in the structure.

As a result of intensive studies by the inventors, a semipermeable membrane having a high-strength separation functional layer was found as a forward osmosis membrane. If the separation functional layer has high strength, even if the structure of the support layer is made sparse and the salt content does not easily accumulate, the decrease in the mechanical strength can be compensated by the separation functional layer itself. That is, the semipermeable membrane of the present invention has high water permeability, excellent solute removal ability, and high mechanical strength, and thus is suitable for continuously obtaining high power generation in concentration difference power generation. .

FIG. 1 is a diagram schematically illustrating a concentration difference power generation apparatus. FIG. 2 shows the results of FT-IR spectra measured for the semipermeable membranes of Examples 2 and 13. FIG. 3 is a chemical formula illustrating the crosslinking reaction of the polymer constituting the dense layer A. FIG. 4 is an explanatory view schematically showing a cross section of the semipermeable membrane produced in Examples 14 and 17.

1. Compound The semipermeable membrane of the present invention comprises at least two layers, a dense layer A having a substantial solute removing ability and a microporous layer B. Among these, the compound which comprises the dense layer A has as a main component the polymer which has a repeating unit represented by the following (Formula 1). This repeating unit forms a polybenzimidazole structure.

The arrangement order of the repeating unit structure shown on the left side of (Formula 1) and the repeating unit structure shown on the right side is not particularly limited, and these repeating unit structures can be arranged randomly.

The structure X, the structures Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ , the structures R ₁ , R ₂ , R ₃ , R ₄ and the constituent ratios m, n of the repeating unit in the above (formula 1) will be described below.

(Structure X)
In the above (Formula 1), the structure X is a hydrophilic group. Specifically, it can have any structure selected from the group consisting of a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof. X is preferably a sulfonic acid group or a salt thereof. By introducing these X structures, the water permeability of the dense layer A, that is, the semipermeable membrane, is improved. As salts of the carboxylic acid group, sulfonic acid group and phosphoric acid group, for example, sodium salts, potassium salts and ammonium salts thereof are preferably used.

M represents the composition ratio (%) of the repeating unit structure including X. On the other hand, n represents the constituent ratio (%) of the repeating unit structure not containing X. m and n are real numbers of 0 or more, and m + n = 100. m: n is preferably in the range of 20:80 to 99: 1, more preferably 30:70 to 90:10, and even more preferably 45:55 to 80:20. The more the repeating unit structure in which the structure X represented by the sulfonic acid group is introduced, the more the water permeability increases, but at the same time, there is a problem that the solubility of the polymer is lowered or the membrane is easily swollen by water molecules. May occur. Therefore, it is preferable that a certain amount of repeating unit structures into which structure X typified by sulfonic acid groups is not introduced are copolymerized. Particularly, when structural units having different chain lengths are copolymerized, the molecular chain regularity is disturbed. This is preferable because a large void is generated and a water-permeable passage is generated to increase water permeability.

However, although details will be described later, even when m is 0, it is possible to sufficiently secure the water permeability of the membrane by selecting a structure containing a hydrophilic group as R ₃ and R ₄ .

A particularly preferred hydrophilic group constituting the structure X is a sulfonic acid group or a salt thereof. The sulfonic acid group may be introduced into the monomer before the polymerization, or may be introduced into the polymer by utilizing some chemical reaction after the polymerization. This is preferable because it can be introduced relatively uniformly into the repeating structure of the acid group. Examples of the method to be introduced after the polymerization include a method of immersing the polymer in fuming sulfuric acid, concentrated sulfuric acid, chlorosulfonic acid, sulfur trioxide and the like.

(Structure Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ )
In the above (Formula 1), the structures Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ have an arbitrary aromatic ring structure. Unless the water permeability (membrane permeation flux) and desalting property (salt removal rate) of the dense layer A constituting the semipermeable membrane of the present invention are significantly impaired, these structures are limited to specific aromatic ring structures. There is no. Specific examples include a structure in which a plurality of aromatic rings composed of a benzene ring, a naphthalene ring, a cardo structure, or a combination thereof are connected.

In the case where Ar ₂ -X including the structure X has any structure selected from the group represented by the following (formula 2), the performance of the dense layer A constituting the semipermeable membrane, polymer synthesis, and raw material for polymer synthesis From the standpoint of ease of synthesis or availability of the monomer.

(In the formula, X is an arbitrary structure selected from a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof.)

Alternatively, Ar ₂ —X containing the structure X may be any structure selected from the group represented by the following (formula 3). These structures have a structure in which aromatic rings are covalently bonded via another atomic group Z.
(Wherein X is an arbitrary structure selected from a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, Z is —O—, —CH ₂ —, It is an arbitrary structure selected from the group consisting of —CO—, —CO ₂ —, —S—, —SO ₂ —, —C (CH ₃ ) ₂ —.

Furthermore, when the structures of Ar ₁ and Ar ₃ , and Ar ₂ and Ar ₄ are the same, it is preferable from the viewpoint of ease of setting the synthesis conditions and economy from the viewpoint that the raw material may be one or two monomers. However, when the structure Ar ₂ -X is selected from the structure group listed in the above (formula 2) (formula 3), the structures of Ar ₁ and Ar ₃ , and Ar ₂ and Ar ₄ are not necessarily the same. Well, the effect of this on the effect of the present invention is negligible. This is because the intermolecular interaction brought about by the structures Ar ₁ , Ar ₂ , Ar ₃ , Ar ₄ is mainly a hydrophobic interaction derived from a ring structure, which is much weaker than a hydrogen bond derived from an imidazole ring and ignored. Because it is as much as possible.

(Structure R ₁ , R ₂ , R ₃ , R ₄ )
In the above (Formula 1), R ₁ , R ₂ , R ₃ and R ₄ are each a hydrogen atom or the structure P. In the present specification, the structure P has an arbitrary structure selected from the group consisting of an alkyl group, an alkyl carboxylic acid or a salt thereof, an alkyl sulfonic acid or a salt thereof, and an alkyl phosphoric acid or a salt thereof. By introducing these structures P into the polymer, the water permeability tends to be improved as compared with those not yet introduced.

The reason for this will be described in detail in the examples. Mainly, the hydrogen bond between polymer molecules is inhibited, and the intermolecular distance is increased to form a space for water flow in the film. This is thought to be possible. This effect can be achieved only with an alkyl group. However, when a hydrophilic group is present at the end of the alkyl group, such as an alkyl carboxylic acid or a salt thereof, an alkyl sulfonic acid or a salt thereof, or an alkyl phosphoric acid or a salt thereof, This is preferable because the effect of improving the amount becomes larger. A more preferable structure P is alkylsulfonic acid or a salt thereof.

When only an alkyl group is introduced, the structure X described above is introduced into the polymer structure at the same time, so that compared with the case where there is a hydrophilic group at the end of the alkyl group such as an alkylcarboxylic acid, The inferior high water permeability effect can be secured. As will be described in detail in the examples, the membrane having the structure P and the hydrophilic group further comprising the structure X has more in the membrane than the membrane having neither of them or only one of them. It can contain water.

As a specific example of the structure P, for example, an alkyl group having 1 or more carbon atoms can be suitably used as the alkyl group. The purpose of introducing an alkyl group into the polymer molecule is to inhibit hydrogen bonding between the polymer molecules and increase the intermolecular distance. The longer the alkyl chain length, the greater the effect of inhibiting hydrogen bonding, and the water permeability tends to improve. The number of carbon atoms constituting the alkyl group may be adjusted according to the target water permeability. The number of carbon atoms constituting the alkyl group is preferably 1 or more, and more preferably 4 or more. Moreover, it is preferable that the carbon number which comprises an alkyl group is 12 or less. When the number of carbon atoms is 13 or more, the effect of inhibiting hydrogen bonding becomes too large, the intermolecular distance is wide, and there is a concern that the salt removability is lowered.

Furthermore, the alkyl group may contain a ring structure, a branched structure, or an unsaturated bond in the structure, and is not limited to only a carbon atom, but may be a nitrogen atom, a sulfur, as long as it is suitably used to increase the intermolecular distance. An atom, a silicon atom, an oxygen atom, etc. may be included.

Examples of the method for introducing the structure P into the polymer include use of a monomer containing the structure P or use of a polymer reaction for the polymer. In particular, the latter method is preferably used from the viewpoint of ease of synthesis. When using the latter method, for example, by using various reducing agents and alkyl halides and reacting with nitrogen atoms in the polymer, the amount of structure P introduced can be controlled by adjusting the concentration and reaction time. Easy and preferable. As an example, if lithium hydride is used as a reducing agent and 1,4-butane sultone is used at the same time, a butylsulfonic acid group can be introduced into the nitrogen atom of the polymer.

In the above (Formula 1), both R ₁ and R ₃ can be hydrogen atoms. Thereby, compared with the case where the structure P is introduced, there is an advantage that the interaction of the polymer becomes stronger, so that the film is easily densified and is preferable in a case where the strength of the film is more important.

(Crosslinking)
The constituent material of the dense layer A constituting the semipermeable membrane of the present invention may include a structure obtained by crosslinking the polymer of (Formula 1). By crosslinking the polymer of (Formula 1), there is an effect of improving the performance as a semipermeable membrane. Examples of the method for forming a cross-link include a method using a chemical reaction between a polymer and a cross-linking agent. The cross-linking agent may be any substance having at least two reactive sites and capable of forming a covalent bond with two or more polymers, and further capable of forming a covalent bond with the nitrogen atom in (Formula 1). The substance is preferable from the viewpoints of a wide selection range of the crosslinking reaction conditions, high reactivity of the crosslinking reaction, and ease of crosslinking. Examples of such a crosslinking agent include various Michael addition type polyfunctional substances, polyfunctional halides, and the like, which are preferable from the viewpoint of availability. Specifically, divinyl sulfone and the like, divinyl ketone and the like, p-xylene dichloride and the like are preferably used. Furthermore, a catalyst such as an acid may be used at the same time if necessary in order to improve the reaction time and the reaction rate.

(polymerization)
The polybenzimidazole that is the main component of the polymer constituting the semipermeable membrane of the present invention is preferably polymerized from an aromatic tetraamine and an aromatic dicarboxylic acid. As a polymerization method, polymerization can be performed by a melt polymerization method described in JOURNAL of Polymer Science, 50, 511 (1961), US Pat. No. 3,509, 108, or the like. Specifically, the polymerization is started at a temperature of about 100 ° C. to 160 ° C., and the temperature is gradually raised from 140 ° C. to about 350 ° C. If the degree of polymerization is to be increased, the polymerization is performed by reducing the pressure after raising the temperature. Preferably it is done. The temperature can be changed from time to time depending on the polymer structure and catalyst. As the catalyst, polyphosphoric acid (hereinafter abbreviated as PPA) or a methanesulfonic acid-niline pentoxide mixture (10: 1 weight ratio) Eaton reagent (hereinafter abbreviated as PPMA). It is preferable to use it.

Examples of aromatic tetraamine monomers that can be used include 1,2,4,5-tetraaminobenzene, 1,2,5,6-tetraaminonaphthalate, 2,3,6,7-tetraaminonaphthalate, 3, 3 ′, 4,4′-tetraaminodiphenylmethane, 3,3 ′, 4,4′-tetraaminodiphenylethane, 3,3 ′, 4,4′-tetraaminodiphenyl-2,2-propane, 3,3 As an example, '4,4'-tetraaminodiphenylthioether and 3,3', 4,4'-tetraaminodiphenylsulfone and their derivatives can be mentioned.

Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, phthalic acid, diphenyldicarboxylic acid Acid, diphenyl ether dicarboxylic acid, 4,4 ′-[1,4-phenylenebis (oxy)] bisbenzoic acid, 4,4′-dicarboxydiphenyl sulfone, diphenoxyethanedicarboxylic acid, 5-sodium sulfoisophthalic acid, hydroxy Isophthalic acid, aminoisophthalic acid, 5-N, N-dimethylaminoisophthalic acid, 5-N, N-diethylaminoisophthalic acid, 2,5-dihydroxyterephthalic acid, 2,6-dihydroxyisophthalic acid, 4,6-dihydroxyisophthalic acid Acid, 2,3-dihydroxyphthalic acid 2,4-dihydroxyphthalic acid, 3,4-dihydroxyphthalic acid, 3-fluorophthalic acid, 5-fluoroisophthalic acid, 2-fluoroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid, and Those derivatives can be mentioned as an example.

2. Semipermeable membrane The semipermeable membrane of the present invention is a semipermeable membrane comprising at least two layers of a dense layer A having a substantial solute removing ability and a microporous layer B, and at least the dense layer A is The main component is the polymer of (Formula 1) or a crosslinked product thereof.

The semipermeable membrane of the present invention has a membrane permeation flux of 0.05 (m ³ / m) when measured at a pressure of 1 MPa, a sodium chloride concentration of the supply liquid of 500 ppm, a temperature of 25 ° C., and a pH of 6.5. ² / day) or more, preferably 0.1 (m ³ / m ² / day) or more, and more preferably 0.4 (m ³ / m ² / day) or more. . Further, the desalting rate is preferably 10% or more, more preferably 20% or more, and further preferably 30% or more. By using a semipermeable membrane having a membrane permeation flux and a desalination rate equal to or higher than this performance, concentration difference power generation can be suitably performed.

(Dense layer A)
The dense layer A is required to have a solute removing ability. Specifically, when measuring at a pressure of 1 MPa, a sodium chloride concentration of the supply liquid: 500 ppm, a temperature of 25 ° C., and a pH of 6.5, it exhibits the ability to remove sodium chloride simultaneously with water permeability. Each performance is as described above.

The thickness of the dense layer A is preferably less than 20 μm. The dense layer A may have a thickness of 5 μm or less, 2 μm or less, or 1 μm or less. When the thickness of the dense layer A is less than 20 μm, high water permeability is obtained.

The thickness of the dense layer A is preferably 0.1 μm or more. The dense layer A may have a thickness of 0.5 μm or more, or 0.8 μm or more. A particularly high strength is obtained when the thickness of the dense layer A is 0.1 μm or more. When the mechanical strength of the microporous layer B is relatively low, the thickness is preferably 1 μm or more so that the dense layer A itself supports it.

The form of the film is not particularly limited, and may be appropriately selected as necessary. For example, the operating pressure normally used in the concentration difference power generation is about 1 to 3 MPa, but a sufficient strength can be secured even with a thickness of about 1 μm in the case of an equivalent pressurized water permeability test. Furthermore, as long as sufficient water permeability and strength are ensured in use, it may be a flat membrane or a hollow fiber membrane, and if the form of the membrane is selected flexibly according to the required performance and strength Good.

(Microporous layer B)
The microporous layer B is a support layer for the dense layer A. Accordingly, the film is not particularly limited as long as it is a film having a plurality of holes, but preferably has a substantially uniform hole or a hole whose diameter gradually increases from one surface to the other surface, and the strength of the microporous layer B. From the above problem, a membrane having a structure in which the pore diameter on one surface of the membrane is 100 nm or less is preferable. Further, the pore diameter is more preferably in the range of 1 to 100 nm. This is because if the pore diameter is less than 1 nm, the permeation flux tends to decrease. The thickness of the microporous layer B is preferably in the range of 1 μm to 5 mm, and more preferably in the range of 10 to 100 μm. This is because when the thickness is less than 1 μm, the strength of the porous support membrane tends to be lowered, and when it exceeds 5 mm, it becomes difficult to handle.

The material used for the microporous layer B is not particularly limited. For example, polysulfone, polyamide, polyester, cellulose polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene sulfone, homopolymer or copolymer such as polyphenylene oxide, and the like. It can be used alone or blended. Among the above, it is preferable to use cellulose acetate, cellulose nitrate or the like as the cellulose polymer and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile or the like as the vinyl polymer. Among these, homopolymers and copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferable.

The microporous layer B may include a so-called base material and a support layer formed on the base material. The base material may be formed of, for example, a woven fabric or a non-woven fabric, and the support layer may be formed of the material described above as a material used for the microporous support film.

Furthermore, it is preferable that the microporous layer B has a sparse structure in which salt content does not easily accumulate when performing concentration difference power generation using a semipermeable membrane. The sparse structure is required to have as high a porosity of the support membrane as possible, a thickness as thin as possible, a space as straight as possible, and a low flexibility. Usually, when these parameters are set in a preferable range from the viewpoint of suppressing salt retention, mechanical strength is remarkably impaired. However, in the present invention, the dense layer A alone has a self-supporting property so that the mechanical strength is high and the low mechanical strength of the microporous layer B can be compensated. Therefore, it is preferable that the porosity of the support film is as large as possible, the thickness is as thin as possible, the void is as straight as possible, and the flexibility is low.

3. Manufacturing Method The semipermeable membrane of the present invention comprises two layers, a dense layer A and a microporous layer B. These two layers are each produced independently and may be combined thereafter, or the dense layer A and the microporous layer may be combined. The conductive layer B may be produced at the same time.

Examples of a method of producing the dense layer A and the microporous layer B independently and then combining them include a method of arranging the dense layer A on the surface of the microporous layer B. At this time, the dense layer A and the microporous layer B may or may not adhere to each other. When adhered, the dense layer A may be impregnated in the microporous layer B. For example, a liquid film of the dense layer A is disposed on the surface of the produced microporous layer B, and then the solvent is removed to obtain a film structure in which the dense layer A is impregnated in the microporous layer B. You can also

For example, the dense layer A and the microporous layer B can be simultaneously produced by, for example, removing a solvent from one type of liquid film and first proceeding phase separation near the surface of the liquid film to form the dense layer A. After that, the phase separation is continued as it is, so that the lower porous layer B can be a relatively sparse microporous layer B. As another method, the liquid film of the dense layer A can be placed on or brought into contact with the liquid film surface of the microporous layer B, and desolvation can be caused simultaneously from each liquid film. If the final film structure is in accordance with the present invention, the course of the process can be set in any way.

The method for producing a semipermeable membrane includes at least a solution preparation step, a liquid membrane formation step, and a solvent removal step in addition to the polymer polymerization step.

(Solution preparation process)
As the solution preparation step, a step of preparing a film forming stock solution (solution adjustment step) will be described below. Specifically, the solution adjustment step includes a step of mixing a polymer having the structure of (Formula 1) and a solvent as components of the film-forming stock solution. When a cross-linking reaction is used, a necessary cross-linking agent may be mixed at the same time, and this process may include a plurality of steps in order to prepare a uniform transparent film forming solution. For example, the solution adjustment step may include stirring the solution containing each component while heating. Furthermore, the mixing ratio and the order of addition are not particularly limited, and additives other than the polymer and the solvent may further be included as necessary. For example, various salts may be added as a dissolution aid within the range where there is no problem in producing a transparent and uniform solution, and various hydrophilic compounds may be added for the purpose of improving the water permeability of the membrane. .

The amount of each substance added to the volume of the film forming solution is preferably set so as to ensure the uniformity of the film forming solution. However, when insoluble matter is generated, it may be removed by a separation method such as filtration, and the filtrate may be used as a membrane-forming solution. By filtering the film-forming solution before coating, good coating properties can be obtained, and the occurrence of defects after film formation can be prevented. In the filtration, a pressure filter can be used according to the high viscosity of the solution. In order to obtain a high effect by filtration, in particular, the filtration diameter is 3 μm or less, preferably 1 μm or less, more preferably 0.4 μm or less, and further preferably 0.2 μm or less.

(Liquid film formation process)
The manufacturing method may include a step of forming a liquid film with a film forming solution (liquid film forming step).

For forming the liquid film, various methods such as dip coating, spin coating, and application using an applicator can be used. When the film thickness of the dense layer A is desired to be several μm or less, the application by spin coating is particularly preferable. The formation of the liquid film can be realized by, specifically, forming a sheet-like flat film by applying a film-forming solution to the substrate. When forming a hollow fiber film, the hollow fiber-like microporous structure is formed in advance. The layer B may be formed and the outer surface may be coated with a solution, or the solution may be passed through the inner surface to coat the inner surface. Furthermore, you may produce the dense layer A and the microporous layer B simultaneously using composite spinning. Specifically, the solution of the dense layer A and the solution of the microporous layer B are simultaneously extruded with a double die, one is an inner layer, the other is an outer layer, and a liquid film is formed at the same time. Also good.

(Desolvation process)
The manufacturing method of the semipermeable membrane of this invention includes performing a solvent removal after a liquid film formation process.

In the present solvent removal step, there are two methods for removing the solvent: a method by heat drying and a method of immersing in a liquid that is compatible with the solvent and is a poor solvent for the polymer.

In the case of solvent removal by heat drying, the solvent is evaporated by heat drying to promote polymer aggregation and form a film. On the other hand, in the case of liquid immersion, phase separation proceeds due to the outflow of the solvent into the liquid, the polymer is solidified, and a film is obtained. Moreover, you may combine these methods. For example, liquid immersion after heating, or heat drying after liquid immersion may be performed. By combining these methods, it is possible to variously control the cross section and surface structure of the obtained film.

When removing the solvent by heat drying, the drying temperature is preferably 100 ° C. or higher and 250 ° C. or lower, more preferably 110 ° C. or higher and lower than 180 ° C., and further preferably 120 ° C. or higher and lower than 150 ° C. preferable. The drying time at this time is preferably from 1 minute to less than 120 minutes, more preferably from 10 minutes to less than 90 minutes, and even more preferably from 30 minutes to less than 60 minutes.

(Other processes)
The method for producing a semipermeable membrane may further include other steps. As another process, for example, the semipermeable membrane formed in the solvent removal process is washed with hot water. Such hot water washing treatment improves the mobility of the polymer and promotes the reorganization of the polymer. As a result, a denser film can be obtained. Since this step can improve the desalting property of the semipermeable membrane, it may be carried out as necessary.

3. Utilization of Semipermeable Membrane The concentration difference power generation method using the permeable membrane of the present invention thus obtained will be described by way of example using a flat membrane-like semipermeable membrane, but is limited to the following method. Not a thing. The concentration difference power generation method of the present invention includes (a) water from low-concentration salt water to high-concentration salt water by bringing low-concentration salt water and high-concentration salt water into contact with each other by any of the semipermeable membranes or composite membranes described above. And (b) driving the generator using the flow.

The semipermeable membrane is made up of a cylindrical water collecting pipe with a large number of holes, along with a raw water channel material such as plastic net, a permeate channel material such as tricot, and a film for increasing pressure resistance as required. By being wound around, it is suitably used as a spiral type semipermeable membrane element.

As shown in FIG. 1, the semi-permeable membrane or an element using the semi-permeable membrane is brought into contact with one side (first surface) of the semi-permeable membrane while pressing high-concentration salt water Sw, and the opposite surface (second surface). When the low-concentration fresh water Fw is brought into contact with the surface, a part of the low-concentration fresh water Fw on the second surface side moves to the first surface side through the semipermeable membrane 1 by the permeation phenomenon (step (a) )). As a result, the volume on the first surface side is increased by the amount of low-concentration fresh water that has permeated from the second surface side, so that the generator 2 is driven at a pressure larger than the pressure input to the first surface side. (Step (b)). Thus, energy used for power generation can be obtained.

By using the semipermeable membrane described above, it has high water permeability even with a small pressure difference, and the retention of salt in the membrane of the semipermeable membrane is suppressed, thereby reducing the amount of water permeability due to concentration polarization. Is suppressed. As a result, according to the power generation method of the present invention, a high power generation amount can be realized.

Next, the present invention will be described based on examples, but the present invention is not necessarily limited thereto.

As described in Tables 1 to 4, 19 types (Examples 1 to 17 and Comparative Example 1) in which the structure of the polymer constituting the dense layer A, the thickness of the dense layer A, the desolvation conditions during film formation, and the like were varied. The semipermeable membranes (2) to (2) were prepared, and their membrane permeation flux and salt removal rate were evaluated.

<Synthesis of monomer>
A monomer to be used for synthesizing a polymer as a main component of the dense layer A was prepared by the following procedure.

３， 3,3'-diaminobenzidine (manufactured by Tokyo Chemical Industry Co., Ltd.) was purchased and used as an aromatic tetraamine monomer.

As the aromatic dicarboxylic acid monomer, a commercially available product was appropriately used. Furthermore, the aromatic dicarboxylic acid monomer was used for polymerization after introducing sodium sulfonate as a hydrophilic group, if necessary. Specifically, a 30% fuming sulfuric acid was brought into contact with an aromatic dicarboxylic acid compound in an excessive amount and reacted at 90 ° C. for 3 to 8 hours to synthesize a sulfonated aromatic dicarboxylic acid. The sulfonation rate was controlled by adjusting the reaction time. Subsequently, a sulfonic acid sodium salt of an aromatic dicarboxylic acid was synthesized by treatment with a saline solution.

<Polymer synthesis>
The polymer was polymer synthesized (polymerized) basically by polymerization of an aromatic tetraamine monomer and an aromatic dicarboxylic acid monomer. First, a total amount of 3 g of aromatic dicarboxylic acid monomer and 0.5 g of polyphosphoric acid catalyst were added to the polymerization vessel and melted at 150 ° C. in a nitrogen atmosphere. After slowly cooling to room temperature, 2 g of 3,3′-diaminobenzidine was added, and the temperature was raised again to 150 ° C. After heating up to 200 degreeC over 5 hours, superposition | polymerization was performed at 200 degreeC for 24 hours. In addition, two types of monomers were mixed and used for the aromatic dicarboxylic acid monomer as needed. After completion of the polymerization, the reaction vessel was cooled, washed with ice water and a 30% aqueous sodium bicarbonate solution, and dried under reduced pressure to obtain 5 g of a polybenzimidazole polymer.

See Tables 1-4 for specific polymer structures to be produced.

Subsequently, the structure P was introduced onto the nitrogen atom in the polymer as necessary so that the polymer structures shown in Tables 1 to 4 were obtained. After adding 10 g of the synthesized polybenzimidazole to the reaction vessel, 5 equivalents of lithium hydride, butyl bromide (Examples 7 and 8) or 1,4-butane sultone (implementation) with respect to the amount of the polybenzimidazole repeating unit structure. 0.5 or 1 equivalent of Example 9, 10) was added and reacted at 90 ° C. for 12 hours. The introduction rate of structure P was adjusted by the amount of butyl bromide or 1,4-butane sultone added. For example, in Examples 7 to 10, it was confirmed by proton NMR measurement that the introduction rate was 50% when 0.5 equivalent was added and the introduction rate was 100% when 1 equivalent was added before film formation.

<Film formation experiment>
Next, a film formation experiment will be described. As a representative example, the present invention will be described in the case of a flat membrane.

(1) Solution preparation A polymer and a dimethyl sulfoxide solvent were added to a glass container so that the polymer concentration was 15 wt%, and stirred at 100 ° C to prepare a transparent and uniform solution. Further, after slowly cooling to room temperature, 1 mol% of divinyl sulfone as a cross-linking agent was added as necessary and dissolved by stirring again (when a cross-linking agent was added here, in the remarks column of Tables 1 to 4, “ "Crosslinking" was provided). This was filtered using a membrane filter having a pore diameter of 0.4 μm, vacuum degassed, and allowed to stand at room temperature for 24 hours, and then used for film formation.

(2) Liquid film formation Film formation was performed by the coating method of the polymer solution. A polymer solution was applied / spin-coated on a silicon wafer to form a liquid film on the substrate. Only in Example 17, the surface of the microporous layer B was placed on the surface of the liquid film, coated, and then subjected to subsequent desolvation.

(3) Desolvation, etc. After forming the liquid film, the solvent was removed by heat drying (120 ° C. for 60 minutes, and further heat drying at 170 ° C. for 30 minutes). After removing the solvent, the film was peeled from the substrate in pure water at room temperature, and then placed on the microporous layer B, and used for a pressurized water permeability test.

<Pressure permeability test>
Before the water permeability test, all the membrane samples were immersed in an isopropyl alcohol aqueous solution for a certain period of time. The water permeability test was performed at a pressure of 1 MPa, a sodium chloride concentration of the supply liquid of 500 ppm, a temperature of 25 ° C., and a pH of 6.5. In all experiments, the membrane area and measurement time were all unified, and the membrane permeation flux [m ³ / m ² / day] and the salt removal rate [%] were measured.
Salt removal rate = 100 × {1- (salt concentration in permeated water / salt concentration in feed water)}

(Measurement of film thickness)
The semipermeable membrane was fixed to a stainless steel plate and dried at 60 ° C. for 12 hours or more, and then two separate portions were arbitrarily cut out to prepare samples. The cross-sectional area of the sample was observed with a scanning electron microscope, and the thickness of an arbitrary place was measured at five points per sample with the attached length measurement software. The thicknesses of the obtained 10 points were totaled and then divided by 10 to calculate the thickness of the semipermeable membrane. Tables 1 to 4 show the relationship between the polymer structure of the dense layer A constituting the formed semipermeable membrane and the membrane performance. Thereafter, the same polysulfone support membrane was used for the microporous layer B unless otherwise specified. The polysulfone supporting membrane used had a surface pore diameter of 30 nm, a thickness of 50 μm, and a porosity of 20%. No tearing or clogging occurred even when used in a 1 MPa pressurized water permeability test.

<Effect of structure X>
In Examples 1 to 6 and Comparative Example 1, the solvent removal conditions and the microporous layer B are the same. These are mainly different from each other in the value of m indicating the introduction rate of X. In Examples 1 to 6, suitable water permeability was obtained, and in Examples 1 to 4, more suitable water permeability was obtained. Comparative Example 1 showed the case where m = 0 and R ₃ and R ₄ were hydrogen atoms, but no suitable water permeability was obtained.

From the above, it is desirable to include the structure X in order to obtain a suitable water permeability, and it is considered that a better water permeability can be obtained particularly when the value of m is 20 or more and less than 100.

<Effect of structure P>
Examples 7 to 10 and Comparative Example 1 are examples having no structure X in which m = 0 and n = 100. In Examples 7 and 8, a butyl group was introduced as the structure P. In Examples 9 and 10, a sodium butylsulfonate group was introduced as structure P. Here, x indicates the introduction rate of the structure P, and 0 ≦ x ≦ 1. In Examples 7 and 9, x = 0.5, and in Examples 8 and 10, x = 1.

In Comparative Example 1 having no structure P, suitable performance was not obtained, but in Examples 7 to 10, suitable performance was shown in any case. The effect of introducing the structure P was confirmed. In the case of crosslinking, the effect of introducing the structure P becomes more prominent. This will be described at the end of the following <Effect of crosslinking>.

<Effect of cross-linking>
In Examples 11 to 15 and Comparative Example 2, crosslinking was examined. Of these, Examples 11 to 14, 17 and Comparative Example 2 are examples that do not have the structure X in which m = 0 and n = 100. As a cross-linking agent, 1 mol% of divinyl sulfone was used with respect to the amount of the repeating unit of the polymer. Except for the polymer in which the hydrophilic group was not introduced in Comparative Example 2, the polymer introduced with the hydrophilic group or structure P obtained high performance by crosslinking. In particular, in Examples 13 and 14, both the amount of water permeation and salt removability improved dramatically.

The progress of the crosslinking reaction was confirmed by FT-IR spectrum measurement. As a representative example, the measurement results of the films of Examples 2 and 16 are shown in FIG. 2, and the crosslinking reaction formula is shown in FIG. As the cross-linking reaction proceeds, an O = S = O structure is formed in the structure of the cross-linked polymer. Therefore, the progress of cross-linking can be confirmed by comparing the presence / absence of this structural site before and after cross-linking. As shown in FIG. 2, in Example 2 (without crosslinking), the peak of asymmetric vibration of O = S = O and the peak of symmetrical vibration were not observed, but in Example 16 (with crosslinking), O = S = O. asymmetric peak vibration and symmetric vibrations, respectively 1307Cm ^-1, was confirmed in 1130 cm ^-1. From this, the progress of the crosslinking reaction was confirmed.

<Effect of moisture content of membrane>
Table 5 shows the results of measuring the water content of the semipermeable membranes obtained in Examples 12 and 14 and Comparative Example 2. The moisture content is measured by vacuum drying the membrane for more than one night and immersing it in RO water (reverse osmosis membrane permeate) overnight, and then removing the water droplets adhering to the membrane surface with Kimwipe. Using the weight W1 and the weight W0 of the dried film, it is expressed as
Moisture content (%) = 100 (%) x (W1-W0) / W0

From Table 5, it was found that the moisture content increased when the structure P was introduced compared to the case where the structure P was not introduced. In general, a membrane having a higher water content is more hydrophilic and suitable as a semipermeable membrane. In Example 12, the structure P was a butyl group, and in Example 14, the structure P was a sodium butylsulfonate group. Since the latter had a higher water content, it can be said to be a more suitable semipermeable membrane. From the viewpoint of the performance shown in Fig. 4, it can be seen that the water permeability increased with the increase of the moisture content. From these, a more suitable semipermeable membrane was obtained by introducing the structure P, and the effect of the structure P could be confirmed.

<Effect of impregnation into microporous layer B>
In Examples 14 and 17, the dense layer A is exactly the same, but only the microporous layer B is different. The difference between Example 14 and Example 17 is whether or not the dense layer A is impregnated in the microporous layer B. In Example 14, after the dense layer A is formed alone, it is only disposed on the upper part of the microporous layer B, so the dense layer A is not impregnated in the microporous layer B. In Example 17, a PVDF support membrane (surface pore diameter is 30 nm, film thickness is 50 μm, porosity is 20%), the surface of the PVDF support membrane is bonded to the surface of the liquid film formed on the substrate, and the solvent is removed. went. Thus, in Example 17, since the dense layer A disposed the microporous layer B at the liquid film stage, the dense layer A impregnates the microporous layer B. A schematic cross-sectional view of the films of Examples 14 and 17 is shown in FIG.

On the other hand, comparing the performance of both, the water permeability and salt removal rate of Example 17 were further improved as compared to Example 14. This is because when the dense layer A is impregnated into the microporous layer B, the crosslinked polymer constituting the dense layer A enters the region of several tens of nanometers, which is the pore diameter of the support membrane (microporous layer B). It is considered that excessive swelling exceeding the pore diameter of the support membrane was prevented, and salt outflow was suppressed. From the above, when the dense layer A was impregnated into the microporous layer B, a semipermeable membrane with higher performance was obtained.

The present invention is suitable as a semipermeable membrane used for concentration difference power generation in which a generator is driven using the flow from low-concentration salt water to high-concentration salt water generated when two liquids having different salinity concentrations are separated by a semipermeable membrane. Can be used.

1 Semipermeable membrane 2 Generator Sw Brine Fw Fresh water

Claims

A semipermeable membrane comprising at least two layers of a dense layer A having a substantial solute removing ability and a microporous layer B,
A semi-permeable membrane whose main component is a polymer in which the dense layer A has a repeating unit structure represented by the following (formula 1).

(In the formula, Ar 1 , Ar 2 , Ar 3 and Ar 4 are each an arbitrary aromatic ring structure, and R 1 , R 2 , R 3 and R 4 are each a hydrogen atom or a structure P, and the structure P is An alkyl group, an alkyl carboxylic acid or a salt thereof, an alkyl sulfonic acid or a salt thereof, an alkyl phosphoric acid or a salt thereof, and X is a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof , A phosphoric acid group or a salt thereof, m and n represent the constituent ratio (%) of the repeating unit structure, m ≧ 0, n ≧ 0, m + n = 100 is satisfied, m = When 0, at least one of R 3 and R 4 is the structure P.)
The semipermeable membrane according to claim 1, wherein in (Formula 1), m: n is in the range of 20:80 to 99: 1.
The half polymer according to any one of claims 1 to 2, wherein the polymer having a repeating unit structure represented by (formula 1) includes a structure in which the polymers are crosslinked by a covalent bond through N atoms in the structure. Permeable membrane.
The semipermeable membrane according to any one of claims 1 to 3, wherein, in (Formula 1), X is a sulfonic acid group or a salt thereof.
The semipermeable membrane according to any one of claims 1 to 4, wherein, in the (formula 1), Ar 2 -X has any structure selected from the group represented by the following (formula 2).

(In the formula, X is an arbitrary structure selected from a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof.)
The semipermeable membrane according to any one of claims 1 to 4, wherein in the (formula 1), Ar 2 -X has any structure selected from the group represented by the following (formula 3).

(Wherein X is an arbitrary structure selected from a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, Z is —O—, —CH 2 —, (It is an arbitrary structure selected from the group consisting of —CO—, —CO 2 —, —S—, —SO 2 —, —C (CH 3 ) 2 —)
The semipermeable membrane according to any one of claims 1 to 6, wherein in (Formula 1), Ar 1 and Ar 3 , and Ar 2 and Ar 4 have the same structure.
The semipermeable membrane according to any one of claims 1 to 7, wherein in (Formula 1), R 1 and R 3 are both hydrogen atoms.
The semipermeable membrane according to any one of claims 1 to 8, wherein, in the (formula 1), the structure P is an alkylsulfonic acid or a salt thereof.
The semipermeable membrane according to any one of claims 1 to 9, wherein in (Formula 1), the alkyl group constituting the structure P is a linear alkyl group having 1 to 12 carbon atoms.
The semipermeable membrane according to any one of claims 1 to 10, wherein the dense layer A is impregnated in the microporous layer B.
Polymerizing a polymer from one or more tetraamine monomers and one or more dicarboxylic acid monomers or dicarboxylic acid derivative monomers;
Preparing a solution containing at least the obtained polymer;
Forming a liquid layer from the solution;
Removing the solvent from the liquid layer;
The method for producing a semipermeable membrane according to any one of claims 1 to 11, comprising forming the dense layer A through a process including at least the following.
Polymerizing a polymer from one or more tetraamine monomers and one or more dicarboxylic acid monomers or dicarboxylic acid derivative monomers;
A step of further introducing the structure P into the polymerized polymer by a polymer reaction;
Preparing a solution containing at least the obtained polymer;
Forming a liquid layer from the solution;
Removing the solvent from the liquid layer;
The method for producing a semipermeable membrane according to any one of claims 1 to 11, comprising forming the dense layer A through a process including at least the following.
Preparing a solution containing at least a polymer having a repeating unit structure represented by (Formula 1) and a crosslinking agent capable of forming a covalent bond with an N atom in the molecule;
Forming a liquid layer from the solution;
A step of proceeding a crosslinking reaction,
Removing the solvent from the liquid layer;
The method for producing a semipermeable membrane according to any one of claims 1 to 11, comprising forming the dense layer A through a process including at least the following.
The method for producing a semipermeable membrane according to any one of claims 12 to 14, further comprising a step of disposing the liquid layer on a surface of the microporous layer B.
Producing a flow of water from the low-concentration salt water to the high-concentration salt water by contacting the low-concentration salt water and the high-concentration salt water through the semipermeable membrane according to any one of claims 1 to 11. And a concentration difference power generation method comprising driving a generator using the flow.