JP2014065004A - Composite semipermeable membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane combining high performance of removing substances other than water and high water permeability.SOLUTION: A composite semipermeable membrane comprises a substrate, a porous support layer formed on the substrate and a separation function layer formed on the porous support layer and having a pleat structure in which convex parts and concave parts are repeated continuously. When cross sections of arbitrarily selected 10 points of a length in the membrane surface direction of 2.0 μm are observed with an electronic microscope, in each cross section, convex parts that meet equation (A) of (X/Y)>1.5, where X is the height of a convex part from the outermost layer of the porous support layer to the top of the convex part and Y is the distance between adjacent concave parts in contact with the front surface of the porous support layer, and have a difference between the maximum Wa and the minimum Wb of the widths of the cavity in a convex part of 20 nm or smaller are present at a density of 10 convex parts/μm or higher.

Description

  The present invention relates to a composite semipermeable membrane useful for the selective separation of liquid mixtures. The composite semipermeable membrane obtained by the present invention can be suitably used for desalination of seawater and brine, for example.

  Regarding the separation of mixtures, there are various techniques for removing substances (eg, salts) dissolved in a solvent (eg, water), but in recent years, the use of membrane separation methods has expanded as a process for saving energy and resources. doing. Membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes can be used for beverages such as seawater, brine, and water containing harmful substances. It is used to obtain water, to manufacture industrial ultrapure water, to treat wastewater, to recover valuable materials.

  The majority of currently marketed reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes, which have an active layer in which a gel layer and a polymer are crosslinked on a porous support membrane, and monomers on the porous support membrane. There are two types, one having an active layer obtained by polycondensation. Among these, a composite semipermeable membrane obtained by coating a support membrane with a separation functional layer made of a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide has water permeability and salt removal performance. Widely used as a high separation membrane (Patent Documents 1 and 2).

  In water production plants using reverse osmosis membranes, higher water permeability is required in order to further reduce running costs. Further, when used as a reverse osmosis membrane, it is required that the above membrane performance can be maintained even during long-time operation at high pressure.

  A factor that affects the performance of the composite semipermeable membrane is a pleated structure formed on the polyamide surface. Regarding the relationship between the membrane performance and the pleat structure, it has been proposed that the substantial membrane area can be increased by extending the folds to improve the water permeability (Patent Documents 3, 4, and 5).

  On the other hand, as a method for improving the salt removal performance, a method of reducing the diameter of the horizontal equivalent circle viewed from the upper surface of the pleat (Patent Document 6) and a method of controlling the pitch and aspect ratio of the pleat have been proposed (Patent Document). 7).

Japanese Patent Laid-Open No. 55-14706 Japanese Patent Laid-Open No. 5-76740 Japanese Patent Laid-Open No. 9-19630 JP-A-9-85068 JP 2001-179061 A Japanese Patent Laid-Open No. 9-141071 JP 2005-169332 A

  As described above, by changing the pleat structure, high salt removal performance and water permeability can be provided, but the size of the pleat tends to be uneven, for example, when there are excessively large pleats, when used at high pressure Crushed and may cause salt removal performance and water permeability performance degradation. An object of the present invention is to solve these problems and provide a composite semipermeable membrane that has both high salt removal performance and water permeability performance.

In order to achieve the above object, the present invention has the following configuration.
(1) A base material, a porous support layer formed on the base material, and a separation functional layer having a pleated structure formed on the porous support layer and having a convex portion and a concave portion continuously repeated A composite semipermeable membrane comprising
When observing arbitrary 10 cross-sections having a length in the film surface direction of 2.0 μm using an electron microscope, each cross-section is a convex portion satisfying the relationship of the following formula (A), and the convex portion A composite semipermeable membrane comprising 10 or more convex portions having a difference between the maximum value and the minimum value of the width of the inner cavity portion of 20 nm or less.
(X / Y)> 1.5 (A)
(X is the height of the convex portion, and the distance from the surface of the porous support layer to the top of the convex portion. Y is the distance between adjacent concave portions in contact with the surface of the porous support layer.)
(2) The composite semipermeable material according to (1), wherein the porous support layer has a multilayer structure of a first layer on a substrate side and a second layer formed on the first layer. film.
(3) The composite semipermeable membrane according to (2), wherein an interface between the first layer and the second layer has a continuous structure.
(4) The porous support layer is contacted with the coagulation bath after the polymer solution A forming the first layer and the polymer solution B forming the second layer are simultaneously coated on the substrate. The composite semipermeable membrane according to (3), which is formed by phase separation.
(5) The composite semipermeable membrane according to (4), wherein the polymer solution A and the polymer solution B have different compositions.
(6) The solid content concentration a (% by weight) of the polymer solution A and the solid content concentration b (% by weight) of the polymer solution B satisfy the relational expression (a / b) ≦ 1.0. The composite semipermeable membrane according to (5).

  According to the present invention, it is possible to achieve both high salt removal performance and water permeability in the composite semipermeable membrane.

FIG. 1 is a diagram schematically illustrating a method of measuring the height of the convex portion and the depth of the concave portion of the separation functional layer. FIG. 2 is a diagram schematically showing a method for measuring the height of the convex portion of the separation functional layer, the distance between adjacent concave portions in contact with the surface of the porous support layer, and the width of the cavity portion inside the convex portion.

1. Composite Semipermeable Membrane A composite semipermeable membrane is a pleat formed by forming a base material, a porous support layer formed on the base material, and a convex portion and a concave portion formed on the porous support layer. And a separation functional layer having a structure. On the surface of the porous support layer, there are 10 convex portions that satisfy the relationship of the following formula (A), and the difference between the maximum value and the minimum value of the width of the cavity inside the convex portion is 20 nm or less. / Μm or more.
(X / Y)> 1.5 (A)
(X is the height of the convex portion, and the distance from the surface of the porous support layer to the top of the convex portion. Y is the distance between adjacent concave portions in contact with the surface of the porous support layer).

(1-1) Separation Functional Layer The separation functional layer is a layer that bears a solute separation function in the composite semipermeable membrane. The composition and thickness of the separation functional layer are set according to the intended use of the composite semipermeable membrane.

  In general, when the height of the convex portion on the separation functional layer (that is, the height of the folds) is increased, the water permeability is improved, but the salt permeability is also increased. It is thought that high salt removal performance and water permeation performance can be achieved by enlarging the height of the folds. As a result of the increase, the salt removal performance is maintained at a high level, and the permeability of the salt is not suppressed. Rather, the presence of excessively expanded pleats leads to deformation at the time of pressurization, and thus membrane structure destruction, and lowers the salt removal performance. In particular, in the case of a membrane for seawater desalination operated at high pressure, this tendency tends to appear in performance.

  Therefore, the present inventors have made extensive studies by paying attention to the pleat structure on the surface. As a result, it has been found that high salt removal performance and water permeation performance can be achieved by making the shape of the folds elongated and uniform.

  In the present invention, the convex portion of the separation functional layer having a pleated structure in which the convex portion and the concave portion are continuously repeated means a convex portion having a height of 1/5 or more of the 10-point average surface roughness. .

  The height of the convex portion of the separation functional layer having a fold structure, the distance between adjacent concave portions in contact with the surface of the porous support layer, and the width of the cavity inside the convex portion are determined by a scanning electron microscope or a transmission electron microscope. Can be observed. For example, for observation with a scanning electron microscope, a composite semipermeable membrane sample is thinly coated with platinum, platinum-palladium, or ruthenium tetroxide, preferably ruthenium tetroxide, and a high resolution field emission type with an acceleration voltage of 3 to 6 kV. Observation is performed using a scanning electron microscope (UHR-FE-SEM). A Hitachi S-900 electron microscope or the like can be used as the high-resolution field emission scanning electron microscope. The observation magnification is preferably 5,000 to 100,000 times, and 10 to obtain the height of the convex portion, the distance between adjacent concave portions in contact with the surface of the porous support layer, and the width of the hollow portion inside the convex portion. 1,000 to 50,000 times is preferable. From the obtained electron micrograph, taking the observation magnification into account, the height of the convex part, the distance between adjacent concave parts in contact with the surface of the porous support layer, and the width of the hollow part inside the convex part are directly measured with a scale, etc. can do.

The 10-point average surface roughness is a value obtained by the following calculation method. First, a cross section perpendicular to the film surface is observed with an electron microscope at the above magnification. In the obtained cross-sectional image, the surface of the separation functional layer (indicated by reference numeral “1” in FIG. 1) appears as a curve of a pleated structure in which convex portions and concave portions are continuously repeated. About this curve, the roughness curve defined based on ISO4287: 1997 is calculated | required. Next, a cross-sectional image is extracted with a width of 2.0 μm in the direction of the average line of the roughness curve (FIG. 1).
The average line is a straight line defined based on ISO 4287: 1997, and is drawn so that the total area of the region surrounded by the average line and the roughness curve is equal above and below the average line in the measurement length. Straight line.
With respect to the extracted image having a width of 2.0 μm, the height of the convex portion and the depth of the concave portion in the separation functional layer are measured using the average line as the reference line 2. The average value is calculated for the absolute values of the heights H1 to H5 of the five convex portions from the highest convex portion to the fifth height, and the depth gradually decreases from the deepest concave portion. Then, an average value is calculated for the absolute values of the depths D1 to D5 of the five recesses up to the fifth depth, and the sum of the two obtained average values is further calculated. The sum thus obtained is the 10-point average surface roughness.

  The height of the folds of the separation functional layer in the present invention (the height of the convex portion, see the symbol X in FIG. 2) is preferably 60 nm or more, more preferably 80 nm or more. Further, the height of the convex portion of the separation functional layer is preferably 800 nm or less, and more preferably 600 nm or less. When the height of the convex portion is 60 nm or more, a composite semipermeable membrane having sufficient water permeability can be easily obtained. Moreover, when the height of the convex portion is 800 nm or less, stable membrane performance can be obtained without being crushed even when the composite semipermeable membrane is operated at high pressure.

  In the fold structure of the separation functional layer in the present invention, the distance between adjacent concave portions in contact with the porous support layer surface (see symbol Y in FIG. 2) is preferably 20 nm or more, more preferably 40 nm or more.

  In the fold structure of the separation functional layer in the present invention, the difference between the maximum value (see symbol Wa in FIG. 2) and the minimum value (see symbol Wb in FIG. 2) of the cavity inside the convex portion is preferably 20 nm or less. is there.

And in the composite semipermeable membrane of the present invention provided with the separation functional layer having a pleated structure in which the convex part and the concave part are continuously repeated, the length in the film surface direction is 2.0 μm using an electron microscope. When the cross sections at 10 locations are observed, the difference between the maximum value and the minimum value of the widths of the cavities inside the convex portions that are the convex portions satisfying the relationship of the following formula (A) in each cross section is 20 nm or less. It is preferable that a certain convex part is contained at 10 pieces / μm or more.
(X / Y)> 1.5 (A)
(X is the height of the convex portion, and the distance from the surface of the porous support layer to the apex of the convex portion. Y is the distance between adjacent concave portions in contact with the surface of the porous support layer. X and Y refer to FIG. ).
By including more than 10 such convex portions / μm, the composite semipermeable membrane has high salt removal performance and water permeability performance, and also can suppress deformation of pleats during pressurization, and is a stable membrane Get performance.

  The separation functional layer may contain polyamide as a main component. The polyamide constituting the separation functional layer can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. Here, it is preferable that at least one of the polyfunctional amine or the polyfunctional acid halide contains a trifunctional or higher functional compound.

  In this document, “X contains Y as a main component” means that Y occupies 60% by weight, 80% by weight, or 90% by weight of X, and X is substantially The structure containing only Y is included.

  The thickness of the separation functional layer is usually preferably in the range of 0.01 to 1 μm and more preferably in the range of 0.1 to 0.5 μm in order to obtain sufficient separation performance and permeated water amount.

  Here, the polyfunctional amine has at least two primary amino groups and / or secondary amino groups in one molecule, and at least one of the amino groups is a primary amino group. An amine, for example, phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, in which two amino groups are bonded to a benzene ring in any of the ortho, meta, and para positions. , 2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, aromatic polyfunctional amines such as 4-aminobenzylamine, aliphatic amines such as ethylenediamine and propylenediamine, 1,2- Examples include alicyclic polyfunctional amines such as diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, and 4-aminoethylpiperazine. It is possible. Among them, considering the selective separation property, permeability, and heat resistance of the membrane, it may be an aromatic polyfunctional amine having 2 to 4 primary amino groups and / or secondary amino groups in one molecule. Preferably, as such a polyfunctional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, it is more preferable to use m-phenylenediamine (hereinafter referred to as m-PDA) from the standpoint of availability and ease of handling.

  These polyfunctional amines may be used alone or in combination of two or more. When using 2 or more types simultaneously, the said amines may be combined and the said amine and the amine which has at least 2 secondary amino group in 1 molecule may be combined. Examples of the amine having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidylpropane.

  The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule. For example, examples of the trifunctional acid halide include trimesic acid chloride, 1,3,5-cyclohexane tricarboxylic acid trichloride, 1,2,4-cyclobutane tricarboxylic acid trichloride, and the like. Aromatic difunctional acid halides such as biphenyl dicarboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalenedicarboxylic acid chloride, aliphatic bifunctional acid halides such as adipoyl chloride, sebacoyl chloride, Mention may be made of alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride. In consideration of the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride. In view of selective separation of the membrane and heat resistance, the polyfunctional acid chloride is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Among these, it is more preferable to use trimesic acid chloride from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination of two or more.

(1-2) Support Membrane In the present invention, the support membrane comprises a base material and a porous support layer, and has substantially no separation performance such as ions, but has a separation performance substantially. This is to give strength to the layer.

For the material of the porous support layer, polysulfone, polyethersulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, and the like homopolymers or copolymers alone or blended. Can be used. Here, cellulose acetate and cellulose nitrate can be used as the cellulose polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and the like can be used as the vinyl polymer. Among them, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferable. More preferred is cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone. Among these materials, polysulfone is highly stable chemically, mechanically and thermally, and is easy to mold. Can be used generally.
Specifically, it is preferable to use polysulfone composed of repeating units represented by the following chemical formula because the pore diameter is easy to control and the dimensional stability is high.

The polysulfone preferably has a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard substance, preferably in the range of 10,000 to 200,000, or 15,000 to 100,000. It is what. When Mw is 10,000 or more, preferable mechanical strength and heat resistance can be obtained as the porous support layer. Moreover, when Mw is 200000 or less, the viscosity of the solution falls within an appropriate range, and good moldability can be realized.
For example, an N, N-dimethylformamide (hereinafter referred to as DMF) solution of the above polysulfone is cast on a substrate to a certain thickness, and wet coagulated in water, so that most of the surface has a diameter number. A porous support layer having fine pores of 1 to 30 nm can be obtained.

  The thickness of the support membrane affects the strength of the composite semipermeable membrane and the packing density when it is used as a membrane element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support membrane is preferably in the range of 30 to 200 μm, more preferably in the range of 50 to 150 μm. The thickness of the porous support layer is preferably in the range of 10 to 100 μm, more preferably in the range of 20 to 80 μm. The thickness of the substrate is preferably in the range of 10 to 200 μm, more preferably in the range of 20 to 150 μm.

  In the present specification, unless otherwise specified, the thickness of each layer and film means an average value. Here, the average value represents an arithmetic average value. That is, the thickness of each layer and film is obtained by calculating the average value of the thickness of 20 points measured at intervals of 20 μm in the direction orthogonal to the thickness direction (direction along the surface of the film) in cross-sectional observation. In addition to measurement by cross-sectional observation, it can be measured by a digital thickness gauge. In addition, since the thickness of the separation functional layer is very thin compared with the support membrane, the thickness of the composite semipermeable membrane can be regarded as the thickness of the support membrane. Therefore, the thickness of the porous support layer can be simply calculated by measuring the thickness of the composite semipermeable membrane with a digital thickness gauge and subtracting the thickness of the substrate from the thickness of the composite semipermeable membrane. The digital thickness gauge can use PEACOCK of Ozaki Mfg. Co., Ltd. In the case of using a digital thickness gauge, it is obtained by measuring the thickness at 20 locations and calculating an average value.

  In the present invention, the porous support layer preferably has a multilayer structure. The porous support layer having a multilayer structure is composed of two layers: a first layer in contact with the substrate and a second layer in contact with the separation functional layer. The first layer plays a role of transferring a monomer such as an amine necessary for forming the separation functional layer to the polymerization field. In order to efficiently transfer the monomer, it is preferable to have continuous pores, and the pore diameter is preferably 0.1 μm or more and 1 μm or less. The second layer serves as a polymerization field and serves to supply the monomer to the separation function layer to be formed by holding and releasing the monomer, and also serves as a starting point for pleat growth. Depending on the monomer holding capacity at this time, the release rate and the supply amount, and the layer structure, the convex portion and the concave portion are continuously repeated, the height of the concave portion of the pleated structure, and the adjacent concave portion in contact with the surface of the porous support layer It is possible to control the distance between them and the width of the cavity inside the convex portion. As a result of intensive studies by the present inventors, it has been found that when the first layer has a sparse structure and the second layer has a dense structure and a uniform surface, the fold shape of the separation functional layer becomes an elongated columnar shape. . In order to make the first layer sparse, for example, there is a method of lowering the concentration of the undiluted polymer solution. In order to make the second layer a dense structure and a uniform surface, for example, there is a method of increasing the concentration of the stock polymer solution.

  Furthermore, the porous support layer of the present invention preferably has a continuous structure at the interface between the first layer and the second layer formed on the first layer. The continuous structure in the present invention refers to a structure in which no skin layer is formed at the interface between the first layer and the second layer formed on the first layer. The skin layer here means a portion having a high density. Specifically, the surface pores of the skin layer are in the range of 1 nm to 50 nm. When a skin layer is formed at the interface between the first layer and the second layer, a high resistance is generated in the porous support layer, and as a result, the permeation flow rate is dramatically reduced.

  Examples of the substrate constituting the support film include polyester polymers, polyamide polymers, polyolefin polymers, and mixtures and copolymers thereof, but mechanical strength, heat resistance, water resistance, and the like. From the standpoint of obtaining an excellent porous support membrane, the polyester polymer is preferred.

  The polyester polymer used in the present invention is a polyester composed of an acid component and an alcohol component. Examples of the acid component include aromatic carboxylic acids such as terephthalic acid, isophthalic acid and phthalic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexanecarboxylic acid. Further, as the alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, or the like can be used.

  Examples of the polyester polymer include polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polylactic acid resin, and polybutylene succinate resin. Examples include coalescence.

  The fabric used for the substrate is preferably a fibrous substrate in terms of strength, unevenness forming ability, and fluid permeability. As a base material, both a long fiber nonwoven fabric and a short fiber nonwoven fabric can be used preferably. In particular, long-fiber non-woven fabrics have excellent permeability when casting a polymer solution on a base material, and the porous support layer peels off, and the film becomes non-uniform due to fluffing of the base material. And the occurrence of defects such as pinholes can be suppressed. In addition, since the base material is made of a long-fiber non-woven fabric composed of thermoplastic continuous filaments, it suppresses non-uniformity and membrane defects during casting of a polymer solution caused by fuzz that occurs when a short-fiber non-woven fabric is used. be able to. Moreover, in continuous membrane formation of a separation membrane, it is preferable to use a long-fiber non-woven fabric that is more excellent in dimensional stability because the tension is applied in the film-forming direction.

  In the long-fiber nonwoven fabric, in terms of moldability and strength, it is preferable that the fibers in the surface layer on the side opposite to the porous support layer have a longitudinal orientation than the fibers in the surface layer on the porous support layer side. According to such a structure, not only a high effect of preventing film breakage by maintaining strength is realized, but also a lamination including a porous support layer and a substrate when imparting irregularities to a semipermeable membrane Formability as a body is also improved, and the uneven shape on the surface of the semipermeable membrane is stabilized, which is preferable. More specifically, the fiber orientation degree in the surface layer on the side opposite to the porous support layer of the long fiber nonwoven fabric is preferably 0 ° to 25 °, and the fiber orientation degree in the surface layer on the porous support layer side. And the orientation degree difference is preferably 10 ° to 90 °.

  The manufacturing process of the composite semipermeable membrane and the manufacturing process of the membrane element include a heating process, but a phenomenon occurs in which the porous support layer or the separation functional layer contracts due to the heating. This is particularly noticeable in the width direction where no tension is applied in continuous film formation. Since shrinkage causes problems in dimensional stability and the like, a substrate having a small rate of thermal dimensional change is desired. In the nonwoven fabric, when the difference between the fiber orientation degree on the surface layer opposite to the porous support layer and the fiber orientation degree on the porous support layer side surface layer is 10 ° to 90 °, the change in the width direction due to heat is suppressed. Can also be preferred.

Here, the fiber orientation degree is an index indicating the direction of the fibers of the nonwoven fabric substrate constituting the porous support layer. Specifically, the fiber orientation degree is an average value of angles between the film forming direction when continuous film formation is performed, that is, the longitudinal direction of the nonwoven fabric base material, and the fibers constituting the nonwoven fabric base material. That is, if the longitudinal direction of the fiber is parallel to the film forming direction, the fiber orientation degree is 0 °. If the longitudinal direction of the fiber is perpendicular to the film forming direction, that is, if it is parallel to the width direction of the nonwoven fabric substrate, the degree of orientation of the fiber is 90 °. Accordingly, the closer to 0 ° the fiber orientation, the longer the orientation, and the closer to 90 °, the lateral orientation.

  The degree of fiber orientation is determined as follows. Ten small sample samples were taken at random from the nonwoven fabric, and the surface of the sample was photographed with a scanning electron microscope at a magnification of 100 to 1000 times. Direction, film forming direction) is 0 °, and the angle when the width direction (transverse direction) of the nonwoven fabric is 90 ° is measured, and the average value thereof is rounded off to the first decimal place as the fiber orientation degree Ask.

2. Next, a method for manufacturing the composite semipermeable membrane will be described. The manufacturing method includes a support film forming step and a separation functional layer forming step.

(2-1) Support film forming step The support film forming step includes applying a polymer solution to the substrate, impregnating the substrate with the polymer solution, and impregnating the substrate with the solution. The method may include a step of forming a three-dimensional network structure by immersing the polymer in a coagulation bath in which the solubility of the polymer is smaller than that of a good polymer solvent. In addition, the step of forming the support film may further include a step of preparing a polymer solution by dissolving a polymer that is a component of the porous support layer in a good solvent for the polymer.

  In order to obtain a support membrane having a predetermined structure, it is necessary to control the impregnation of the polymer solution into the substrate. In order to control the impregnation of the polymer solution into the substrate, for example, a method of controlling the time until the polymer solution is immersed on the non-solvent after the polymer solution is applied on the substrate, or the temperature of the polymer solution or A method of adjusting the viscosity by controlling the concentration can be mentioned, and these production methods can be combined.

  The time until the polymer solution is applied on the substrate and then immersed in the coagulation bath is preferably in the range of usually 0.1 to 5 seconds. If the time until dipping in the coagulation bath is within this range, the organic solvent solution containing the polymer compound is sufficiently impregnated between the fibers of the base material and then solidified. In addition, what is necessary is just to prepare the preferable range of time until it immerses in a coagulation bath suitably with the viscosity of the polymer solution to be used.

  When the polymer solution A forming the first layer contains polysulfone as a material for the porous support layer, the polysulfone concentration (that is, the solid content concentration a) of the polymer solution A is preferably 13% by weight or more and 15% by weight or less. It is. When the polysulfone concentration of the polymer solution A is 13% by weight or more and 15% by weight or less, the communication holes are formed to be relatively small, so that a desired pore diameter can be easily obtained.

  When the polymer solution B forming the second layer also contains polysulfone, the polymer solution B has a polysulfone concentration (that is, a solid content concentration b) of preferably 16 wt% or more and 25 wt% or less. When the polysulfone concentration of the polymer solution B is less than 16% by weight, the surface pores tend to be large, and when the separation functional layer is formed, the amount of monomer supply relative to the monomer retention capacity in the second layer is It becomes too large, and it becomes difficult to form a pleat having a sufficient thickness. Further, when the polysulfone concentration in the polymer solution B exceeds 25% by weight, the surface pores tend to be small, and when the separation functional layer is formed, the monomer supply rate is low, resulting in pleats formed as a result. Becomes non-uniform.

  The solid content concentration a and the solid content concentration b preferably satisfy the relational expression (a / b) ≦ 1.0. Further, it is more preferable that the solid content concentration a and the solid content concentration b satisfy the above-mentioned relational expressions while satisfying the respective preferable numerical ranges described above.

  When using a polysulfone, the temperature of the polymer solution at the time of applying the polymer solution is usually within a range of 10 to 60 ° C. Within this range, the polymer solution does not precipitate and is solidified after sufficiently impregnating the organic solvent solution containing the polymer between the fibers of the substrate. As a result, the porous support layer is firmly bonded to the substrate by the anchor effect, and the support film of the present invention can be obtained. The preferred temperature range of the polymer solution may be appropriately adjusted depending on the viscosity of the polymer solution used.

  In the formation of the support film, it is preferable to apply the polymer solution A forming the second layer at the same time as applying the polymer solution A forming the first layer on the substrate. When a curing time is provided after application of the polymer solution A, a high-density skin layer is formed on the surface of the first layer formed by phase separation of the polymer solution A, and the permeation flow rate is greatly reduced. Therefore, it is preferable to apply the polymer solution A and the polymer solution B at the same time so that the polymer solution A does not form a high-density skin layer by phase separation. For example, “applied simultaneously” means that the polymer solution A is in contact with the polymer solution B before reaching the substrate, that is, when the polymer solution A is applied to the substrate. The polymer solution B is applied on the polymer solution A.

  In the present invention, the ratio of the coating thickness of the polymer solution A and the coating thickness of the polymer solution B at the time of forming the support membrane is preferably 0.15 to 0.30 (coating thickness ratio = polymer solution B). Application thickness / application thickness of polymer solution A). When the coating thickness ratio is within this range, the monomer diffusion rate during interfacial polymerization is increased, the height of the convex portion of the pleat structure is high, and the difference between the maximum value and the minimum value of the width of the cavity inside the convex portion. Is easier to form small folds.

  In the present invention, the difference in viscosity between the low viscosity polymer solution A and the high viscosity polymer solution B is preferably 1000 cP or less. When the viscosity difference is within this range, diffusion of the polymer solution A and the polymer solution B can be suppressed, and a uniform porous support layer surface can be obtained.

  Application of the polymer solution onto the substrate can be carried out by various coating methods, but pre-metering coating methods such as die coating, slide coating, curtain coating and the like that can supply an accurate amount of the coating solution are preferably applied. Further, in the formation of the porous support layer having a multilayer structure of the present invention, the double slit die method in which the polymer solution forming the first layer and the polymer solution forming the second layer are simultaneously applied is more preferably used. It is done.

  The resin contained in the polymer solution A and the polymer solution B may be the same resin or different resins. As appropriate, it can be prepared in a wider range in consideration of various properties such as strength properties, permeability properties, and surface properties of the support membrane to be produced.

  The solvent contained in the polymer solution A and the polymer solution B may be the same solvent or different solvents as long as they are good polymers. As appropriate, it can be prepared in a wider range in consideration of the strength characteristics of the support membrane to be produced and the impregnation of the polymer solution into the substrate.

  The good solvent of the present invention dissolves a polymer material. Examples of good solvents include N-methyl-2-pyrrolidone (hereinafter referred to as NMP); tetrahydrofuran; dimethyl sulfoxide; amides such as tetramethylurea, dimethylacetamide and dimethylformamide; lower alkyl ketones such as acetone and methylethylketone; trimethyl phosphate , Esters and lactones such as γ-butyrolactone, and mixed solvents thereof.

  Examples of the non-solvent of the resin include water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, and low molecular weight. Examples thereof include aliphatic hydrocarbons such as polyethylene glycol, aromatic hydrocarbons, aliphatic alcohols, or mixed solvents thereof.

  The polymer solution may contain an additive for adjusting the pore size, porosity, hydrophilicity, elastic modulus, etc. of the support membrane. Additives for adjusting the pore size and porosity include water, alcohols, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol, water-soluble polymers such as polyacrylic acid or salts thereof, lithium chloride, sodium chloride, chloride Examples include inorganic salts such as calcium and lithium nitrate, formaldehyde, formamide and the like, but are not limited thereto. Examples of additives for adjusting hydrophilicity and elastic modulus include various surfactants.

  As the coagulation bath, water is usually used, but any water that does not dissolve the polymer may be used. The film form of the support film changes depending on the composition, and thereby the film forming property of the composite semipermeable membrane also changes. Further, the temperature of the coagulation bath is preferably -20 ° C to 100 ° C. More preferably, it is 10-40 degreeC. If it is higher than this range, the vibration of the coagulation bath surface becomes intense due to thermal motion, and the smoothness of the film surface after film formation tends to decrease. On the other hand, if it is lower than the above range, the coagulation rate becomes slow, causing a problem in film forming properties.

  Next, the support membrane obtained under such preferable conditions is washed with hot water in order to remove the membrane-forming solvent remaining in the membrane. The temperature of the hot water at this time is preferably 40 to 100 ° C, more preferably 60 to 95 ° C. If it is higher than this range, the degree of shrinkage of the support membrane will increase and the water permeability will decrease. On the contrary, if it is lower than the above range, the cleaning effect is small.

(2-2) Formation process of separation functional layer Next, as an example of the formation process of the separation functional layer constituting the composite semipermeable membrane, formation of a layer mainly composed of polyamide (that is, a polyamide separation functional layer) is given. explain. In the step of forming the polyamide separation functional layer, interfacial polycondensation is performed on the surface of the support membrane using the aqueous solution containing the polyfunctional amine described above and an organic solvent solution immiscible with water containing the polyfunctional acid halide. By doing so, a polyamide skeleton can be formed.

  The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1% by weight to 15% by weight, and more preferably in the range of 0.5% by weight to 12% by weight. Within this range, sufficient water permeability and salt and boron removal performance can be obtained.

  As long as the polyfunctional amine aqueous solution does not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide, a surfactant, an organic solvent, an alkaline compound, an antioxidant, or the like may be contained. The surfactant has the effect of improving the wettability of the porous support membrane surface and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and when added, the interfacial polycondensation reaction may be efficiently performed.

  In order to perform the interfacial polycondensation on the support membrane, first, the polyfunctional amine aqueous solution is brought into contact with the support membrane. The contact is preferably performed uniformly and continuously on the support membrane surface. Specific examples include a method of coating a polyfunctional amine aqueous solution on a support membrane and a method of immersing the support membrane in a polyfunctional amine aqueous solution. The contact time between the support membrane and the polyfunctional amine aqueous solution is preferably in the range of 5 seconds to 10 minutes, and more preferably in the range of 10 seconds to 3 minutes.

  After bringing the polyfunctional amine aqueous solution into contact with the support membrane, the solution is sufficiently drained so that no droplets remain on the membrane. By sufficiently draining the liquid, it is possible to prevent the remaining portion of the droplets from becoming a defect after the formation of the composite semipermeable membrane, thereby reducing the salt removal performance of the composite semipermeable membrane. As a method for draining, for example, as described in JP-A-2-78428, a method of allowing the excess aqueous solution to flow down naturally by holding the support film after contacting the polyfunctional amine aqueous solution in the vertical direction, For example, a method of forcibly draining an air stream such as nitrogen from an air nozzle can be used. In addition, after draining, the membrane surface can be dried to partially remove water from the aqueous solution.

  Next, the support film after contacting with the polyfunctional amine aqueous solution is brought into contact with water containing a polyfunctional acid halide and an immiscible organic solvent solution to form a crosslinked polyamide separation functional layer by interfacial polycondensation.

  The concentration of the polyfunctional acid halide in the organic solvent solution immiscible with water is preferably in the range of 0.01 wt% to 10 wt%, and preferably 0.02 wt% to 2.0 wt%. More preferably within the range. When the polyfunctional acid halide concentration is 0.01% by weight or more, a sufficient reaction rate can be obtained, and when it is 10% by weight or less, the occurrence of side reactions can be suppressed. Further, it is more preferable to include an acylation catalyst such as DMF in the organic solvent solution, since interfacial polycondensation is promoted.

  The water-immiscible organic solvent is preferably one that dissolves the polyfunctional acid halide and does not destroy the support membrane, and may be any one that is inert to the polyfunctional amine compound and polyfunctional acid halide. . Preferable examples include hydrocarbon compounds such as hexane, heptane, octane, nonane and decane.

  The method of bringing the organic solvent solution containing the polyfunctional acid halide into contact with the support membrane may be performed in the same manner as the method of coating the support membrane with the polyfunctional amine aqueous solution.

  In the interfacial polycondensation step of the present invention, the support membrane is sufficiently covered with a crosslinked polyamide thin film, and a water-immiscible organic solvent solution containing a polyfunctional acid halide in contact with the support membrane is left on the support membrane. It is important to keep it. For this reason, the time for performing the interfacial polycondensation is preferably from 0.1 second to 3 minutes, and more preferably from 0.1 second to 1 minute. When the interfacial polycondensation time is 0.1 seconds or more and 3 minutes or less, the support membrane can be sufficiently covered with a crosslinked polyamide thin film, and an organic solvent solution containing a polyfunctional acid halide is supported on the support membrane. Can be held on.

  After the polyamide separation functional layer is formed on the support membrane by interfacial polycondensation, excess solvent is drained. As a method for draining, for example, a method in which a film is held in a vertical direction and excess organic solvent is allowed to flow down and removed can be used. In this case, the time for gripping in the vertical direction is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. If it is too short, the separation functional layer will not be completely formed, and if it is too long, the organic solvent will be overdried and a defective part will occur in the polyamide separation functional layer, resulting in poor membrane performance.

3. Use of composite semipermeable membranes Composite semipermeable membranes have a large number of holes along with raw water channel materials such as plastic nets, permeate channel materials such as tricots, and films to increase pressure resistance as needed. It is wound around a cylindrical water collecting pipe and is suitably used as a spiral type composite semipermeable membrane element. Further, this element can be connected in series or in parallel and housed in a pressure vessel to constitute a composite semipermeable membrane module.

  In addition, the composite semipermeable membrane, the composite semipermeable membrane element, and the composite semipermeable membrane module described above are combined with a pump that supplies raw water to them, a device that pretreats the raw water, and the like to constitute a fluid separation device. Can do. By using this separation device, raw water can be separated into permeated water such as drinking water and concentrated water that has not permeated through the membrane, and water suitable for the purpose can be obtained.

  The higher the operating pressure of the fluid separator, the better the salt removal, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, water to be treated is added to the composite semipermeable membrane. The operating pressure at the time of permeation is preferably 0.5 MPa or more and 8 MPa or less. The operation pressure is a so-called transmembrane pressure. As the feed water temperature increases, the salt removal performance decreases, but the membrane permeation flux decreases as the supply water temperature decreases, so 5 ° C. or higher and 45 ° C. or lower is preferable. In addition, when the pH of the feed water becomes high, scales such as magnesium may be generated in the case of feed water with a high salt concentration such as seawater, and there is a concern about deterioration of the membrane due to high pH operation. Is preferred.

  Examples of the raw water to be treated by the composite semipermeable membrane include liquid mixtures containing TDS (Total Dissolved Solids) of 500 mg / liter to 100 g / liter, such as seawater, brine, and drainage. Generally, TDS refers to the total amount of dissolved solids and is expressed as “mass ÷ volume” or expressed as “weight ratio” by regarding 1 liter as 1 kg. According to the definition, the solution filtered with a 0.45 micron filter can be calculated from the weight of the residue by evaporating at a temperature of 39.5 to 40.5 ° C., but more simply converted from practical salt content.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Various changes and modifications can be made without departing from the technical scope of the present invention.

<Creation of semipermeable membrane>
In the following Examples and Comparative Examples, Polysulfone UDEL p-3500 manufactured by Solvay Advanced Polymers Co., Ltd. was used as the polysulfone.
Example 1
A 13% by weight polysulfone DMF solution (polymer solution A) and a 20% by weight polysulfone DMF solution (polymer solution B) were prepared by heating and maintaining a mixture of each solvent and solute at 90 ° C. for 2 hours. did.
Each of the prepared polymer solutions was cooled to room temperature, supplied to a separate extruder, and filtered with high precision. Thereafter, the filtered polymer solution was passed through a double slit die on a non-woven fabric (thickness: about 90 μm, air permeability: 1.0 cc / cm ² / sec) made of polyester fiber produced by a papermaking method. The polymer solution B was cast simultaneously with a coating thickness of 150 μm and a coating thickness of 45 μm, and immediately immersed in pure water at 25 ° C. and washed for 5 minutes to obtain a support film.

  The obtained support membrane was immersed in a 3.0 wt% aqueous solution of m-PDA for 2 minutes, and then slowly pulled up so that the membrane surface was vertical. Nitrogen was blown from the air nozzle to remove excess aqueous solution from the surface of the support membrane, and then an n-decane solution at 25 ° C. containing 0.12% by weight of trimesic acid chloride was applied so that the membrane surface was completely wetted. After leaving still for 1 minute, in order to remove an excess solution from a film | membrane, the film | membrane surface was hold | maintained vertically for 1 minute, it drained, and it dried by blowing 25 degreeC air using the air blower. Then, the composite semipermeable membrane provided with a base material, a porous support layer, and a polyamide separation functional layer was obtained by washing with water at 45 ° C. for 2 minutes.

(Example 2)
In Example 1, a composite semipermeable membrane in Example 2 was obtained in the same manner as in Example 1 except that the coating thickness of the polymer solution B was 22 μm.

(Example 3)
In Example 1, Example 3 was carried out in the same manner as Example 1 except that lithium chloride was added to the solution of Polymer solution B so that the viscosity difference between Polymer solution A and Polymer solution B was 90 cP. A composite semipermeable membrane was obtained.

Example 4
Example 1 is the same as Example 1 except that a long fiber nonwoven fabric (yarn diameter: 1 dtex, thickness: about 90 μm, air permeability: 1.3 cc / cm ² / sec) made of polyethylene terephthalate fiber is used as the base material in Example 1. Similarly, a composite semipermeable membrane in Example 4 was obtained.

(Comparative Example 1)
A support membrane was obtained by the same procedure as in Example 1 except that only a 20% by weight polysulfone DMF solution was applied on a nonwoven fabric with a thickness of 200 μm using a single slit die instead of a double slit die. A separation functional layer was formed on the obtained support membrane by the same procedure as in Example 1 to obtain a composite semipermeable membrane in Comparative Example 1.

(Comparative Example 2)
A composite semipermeable membrane in Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that a DMF solution containing 15% by weight of polysulfone was used as the polymer solution.

(Comparative Example 3)
In Example 1, a composite semipermeable membrane in Comparative Example 3 was obtained in the same manner as in Example 1 except that the polymer solution A was cast at a thickness of 150 μm and the polymer solution B was cast at a thickness of 60 μm at the same time. .

(Comparative Example 4)
A supporting membrane was obtained by the same procedure as in Comparative Example 1 except that a DMF solution containing 18% by weight of polysulfone was used as the polymer solution. On the obtained support membrane, an aqueous solution containing 3.0% by weight of m-PDA, 0.15% by weight of sodium lauryl sulfate, 3.0% by weight of triethylamine, and 6.0% by weight of camphorsulfonic acid was applied. After leaving still for 1 minute, in order to remove excess solution from the membrane, the membrane surface was held vertically for 2 minutes to drain the solution, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the support membrane. Thereafter, a hexane solution at 25 ° C. containing 0.20% by weight of trimesic acid chloride was applied so that the film surface was completely wetted. After leaving for 1 minute, in order to remove excess solution from the membrane, the membrane surface was held vertically for 1 minute to drain, and then kept in a 120 ° C hot air dryer for 3 minutes to separate the separation functional layer. The composite semipermeable membrane in Comparative Example 4 was obtained.

(Comparative Example 5)
A supporting membrane was obtained by the same procedure as in Comparative Example 1 except that a 17% by weight polysulfone DMF solution was used as the polymer solution. An aqueous solution containing 3.0% by weight of m-PDA was applied on the obtained support film. After leaving still for 1 minute, in order to remove excess solution from the membrane, the membrane surface was held vertically for 2 minutes to drain the solution, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the support membrane. Thereafter, an Isopar L (available from ExxonMobil Corp.) solution at 25 ° C. containing 0.13% by weight of trimesic acid chloride was sprayed so that the membrane surface was completely wetted. After leaving for 1 minute, the membrane surface was held vertically for 1 minute to remove excess solution from the membrane, drained, and then washed with water at room temperature to obtain the composite semipermeable membrane in Comparative Example 5 Obtained.

<Measurement of the height of the convex portion, the distance between adjacent concave portions in contact with the surface of the porous support layer, and the width of the hollow portion inside the convex portion>
A composite semipermeable membrane sample was embedded with an epoxy resin, stained with OsO ₄ to facilitate cross-sectional observation, and cut with an ultramicrotome to prepare 10 ultrathin sections. A cross-sectional photograph of the obtained ultrathin slice was taken using a transmission electron microscope. The acceleration voltage at the time of observation was 100 kV, and the observation magnification was 10,000 times. About the obtained cross-sectional photograph, the height of the convex part and the depth of the concave part at a distance of 2.0 μm in length were measured using a scale, and the 10-point average surface roughness was calculated as described above. Based on this 10-point average surface roughness, the height of the convex portion having a height of 1/5 or more of the 10-point average surface roughness is adjacent to the surface of the porous support layer. The distance between the concave portions and the width of the hollow portion inside the convex portion were measured with a scale. And in the cross section obtained from the cross-sectional photograph by a transmission electron microscope as mentioned above, it is the maximum value of the width | variety of the convex part which satisfy | fills the relationship of the following formula | equation (A), and a convex part inside (FIG. 2). Table 1 shows a convex portion having a difference between the minimum value (see symbol Wb in FIG. 2) and a minimum value (see symbol Wb in FIG. 2) of 20 nm or less as the convex portion of the present invention.
(X / Y)> 1.5 (A)
(X (see FIG. 2) is the height of the convex portion, and the distance from the surface of the porous support layer to the top of the convex portion. Y (see FIG. 2) is between adjacent concave portions in contact with the surface of the porous support layer. Distance.)

<Salt removal performance (NaCl removal rate)>
By supplying evaluation water adjusted to a temperature of 25 ° C., pH 7.0, and sodium chloride concentration of 2000 ppm to the composite semipermeable membrane at an operating pressure of 1.55 MPa, filtration treatment was performed for 3 hours. The obtained permeated water was used for measurement of salt removal performance.
Practical salinity was obtained by measuring the electrical conductivity of the supplied water and the permeated water with an electric conductivity meter manufactured by Toa Radio Industry Co., Ltd. From the NaCl concentration obtained by converting this practical salinity, the salt removal performance, that is, the NaCl removal rate was determined by the following equation. The results are shown in Table 1.
NaCl removal rate (%) = 100 × {1− (NaCl concentration in permeated water / NaCl concentration in feed water)}

<Permeability (membrane permeation flux)>
The amount of permeated water obtained by the above filtration treatment for 3 hours is expressed as a membrane permeation flux (m ³ / m ² / day) with a water permeation amount per cubic meter (m ³ ) per day, and the result Table 1 shows.

  It can be seen that the composite semipermeable membranes of Examples 1 to 4 can achieve both high salt removal performance and water permeability.

  The composite semipermeable membrane of the present invention can be particularly suitably used for brine or seawater desalination.

1 Separation function layer 2 Reference line H1, H2, H3, H4, H5 Height of convex part in pleat structure of separation functional layer D1, D2, D3, D4, D5 Depth of concave part in pleat structure of separation functional layer X Convex Height of part Y Distance between adjacent concave parts in contact with the surface of the porous support layer Wa Maximum value of the width of the cavity inside the convex part Wb Minimum value of the width of the cavity part inside the convex part

Claims (6)

A base material, a porous support layer formed on the base material, and a separation functional layer having a pleated structure formed on the porous support layer and having convex and concave portions continuously repeated. A composite semipermeable membrane,
When observing arbitrary 10 cross-sections having a length in the film surface direction of 2.0 μm using an electron microscope, each cross-section is a convex portion satisfying the relationship of the following formula (A), and the convex portion A composite semipermeable membrane comprising 10 or more convex portions having a difference between the maximum value and the minimum value of the width of the inner cavity portion of 20 nm or less.
(X / Y)> 1.5 (A)
(X is the height of the convex portion, and the distance from the outermost surface of the porous support layer to the top of the convex portion. Y is the distance between adjacent concave portions in contact with the porous support layer surface.)   2. The composite semipermeable membrane according to claim 1, wherein the porous support layer has a multilayer structure of a first layer on a substrate side and a second layer formed on the first layer.   The composite semipermeable membrane according to claim 2, wherein an interface between the first layer and the second layer has a continuous structure.   The porous support layer is applied to the coagulation bath and phase-separated after the polymer solution A forming the first layer and the polymer solution B forming the second layer are simultaneously applied on the substrate. The composite semipermeable membrane according to claim 3, wherein the composite semipermeable membrane is formed.   The composite semipermeable membrane according to claim 4, wherein the polymer solution A and the polymer solution B have different compositions.   The solid content concentration a (wt%) of the polymer solution A and the solid content concentration b (wt%) of the polymer solution B satisfy the relational expression (a / b) ≦ 1.0. 5. The composite semipermeable membrane according to 5.