JP2014065003A - Composite semipermeable membrane and water production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane combining high boron removal performance 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 1 formed on the porous support layer and having a pleat structure in which convex parts H1 to H5 and concave parts D1 to D5 are repeated continuously. When cross sections of arbitrarily selected 10 parts of a length in the membrane surface direction of 2.0 μm are observed with an electron microscope, the average height of protrusions having heights H1 to H5 of a fifth or greater of the 10-point average surface roughness of the separation function layer is equal to or greater than 70 nm, and a standard deviation of membrane thicknesses in the cross sections is equal to or smaller than 2.0 nm.

Description

  TECHNICAL FIELD The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture and a water production method using the membrane. The composite semipermeable membrane obtained by the present invention can be suitably used for seawater desalination.

  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.

  Most of the reverse osmosis membranes and nanofiltration membranes currently on the market are composite semipermeable membranes, which have an active layer in which a gel layer and a polymer are cross-linked on a support membrane, and monomers are polycondensed on the support membrane. There are two types, one with an active layer. In particular, a composite semipermeable membrane obtained by coating a support membrane with a separation functional layer made of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide has water permeability and solute removal properties. Widely used as a high separation membrane.

  By the way, boron has toxicity such as causing onset of nerve damage and growth inhibition to human bodies and animals and plants, but is abundant in seawater. Therefore, boron removal is important in seawater desalination. Therefore, various means for improving the boron removal performance of the composite semipermeable membrane have been proposed (Patent Documents 1 to 3). Patent Document 1 discloses a method for improving boron removal performance by heat treating a composite semipermeable membrane formed by interfacial polymerization. Patent Document 2 discloses a method in which a composite semipermeable membrane formed by interfacial polymerization is brought into contact with a bromine-containing free chlorine aqueous solution. Patent Document 3 discloses a method for achieving both water permeability and boron removal rate by chemically treating the crosslinked polyamide of the separation functional layer with nitrous acid. However, further higher boron removal rates and higher water permeability than those obtained by these techniques are desired.

  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 a substantial membrane area can be increased by extending the pleats to improve water permeability (Patent Documents 4, 5, and 6). However, no mention is made of boron removal performance.

JP-A-11-19493 JP 2001-259388 A JP 2007-90192 A Japanese Patent Laid-Open No. 9-19630 JP-A-9-85068 JP 2001-179061 A

  An object of the present invention is to provide a composite semipermeable membrane capable of achieving both high boron removal performance and high water permeation performance with less eluate and a water production method using the membrane.

  In order to achieve the above object, the composite semipermeable membrane of the present invention comprises 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. A composite semipermeable membrane having a separation function layer having a pleated structure, which is continuously repeated, and was observed by using an electron microscope at any 10 sections having a length of 2.0 μm in the film surface direction. Sometimes, in each cross section, the average height of the protrusions having a height of 1/5 or more of the 10-point average surface roughness of the separation functional layer is 70 nm or more, and the thickness of the separation functional layer in the cross section The standard deviation of is 2.0 nm or less.

  According to the present invention, a composite semipermeable membrane that achieves both high boron removal performance and water permeability is realized, and energy saving and quality of permeated water can be improved.

FIG. 1 is a drawing schematically showing a method for measuring the height of a convex portion of a separation functional layer.

1. Composite semipermeable membrane A composite semipermeable membrane is a support membrane including 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 function layer having a pleated structure.

(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 such as the composition and thickness of the separation functional layer is set according to the purpose of 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 pleats) is increased, the water permeability is improved, but the boron permeability is also increased. It is thought that it is possible to achieve both high water permeability and boron removal performance by enlarging the pleats. The water permeability increased relative to the amount of boron permeated due to increased water permeability. As a result, the boron removal performance is maintained at a high level, and the boron permeability is not suppressed. Rather, the presence of an excessively enlarged convex portion leads to deformation at the time of pressurization, and consequently to membrane structure destruction, and lowers the boron removal performance. In particular, in the case of a membrane for seawater desalination operated at high pressure, this tendency tends to appear in performance.

  In addition, when the thickness of the separation functional layer is non-uniform, boron permeates from the place where the functional layer is partially thinned, so that the boron removal performance is deteriorated.

  Therefore, the present inventors have made extensive studies focusing on the height of the convex portions on the surface and the thickness of the separation functional layer. As a result, by precisely controlling the height of the convex portion and the thickness of the separation functional layer, the height of the convex portion is enlarged, and the thickness of the separation functional layer is made uniform, resulting in high water permeability and boron removal. It was found that the performance can be compatible.

The convex part of the separation functional layer in the present invention means a convex part having a height of 1/5 or more of the 10-point average surface roughness. 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 following 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. 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.
In 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 function 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. The 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 absolute values of the two obtained average values is calculated. The sum thus obtained is the 10-point average surface roughness.

  The thickness of the separation functional layer and the height of the convex portion can be analyzed using an observation technique such as a transmission electron microscope (TEM), TEM tomography, or a focused ion beam / scanning electron microscope (FIB / SEM). For example, after embedding a composite semipermeable membrane sample with an epoxy resin, the composite semipermeable membrane sample is dyed with osmium tetroxide or ruthenium tetroxide, preferably osmium tetroxide, and further subjected to surface processing with a glass knife or a diamond knife and 100 nm or less. An ultrathin section is prepared and observed using a transmission electron microscope at an acceleration voltage of 50 to 200 kV. A transmission electron microscope (Hitachi, H7100FA) or the like can be used. The observation magnification is preferably 5,000 to 100,000 times, and preferably 20,000 to 100,000 times for obtaining the thickness of the separation functional layer and the height of the convex portion. In order to obtain the thickness of the separation functional layer and the height of the convex portion, it can be directly measured with a scale or the like in consideration of the observation magnification from the obtained electron micrograph.

  The height of the convex portion is a value measured for a convex portion having a height of 1/5 or more of the 10-point average surface roughness. The average height of the convex portion is measured as follows. In the composite semipermeable membrane, when 10 sections are observed, the height of the convex portion which is 1/5 or more of the above-mentioned 10-point average surface roughness is measured in each section. The average height per convex part is calculated. Furthermore, the average height is obtained by calculating the arithmetic average based on the calculation results for the 10 cross sections. Here, each cross section has a width of 2.0 μm in the direction of the average line of the roughness curve.

  The height of the convex portion of the separation functional layer in the present invention is preferably 70 nm or more, more preferably 90 nm or more. In addition, the height of the convex portion of the separation functional layer is preferably 1000 nm or less, and more preferably 800 nm or less. When the height of the convex portion is 70 nm or more, a composite semipermeable membrane having sufficient water permeability can be easily obtained. Moreover, when the height of the convex portion is 1000 nm or less, stable membrane performance can be obtained without the convex portion being crushed even when the composite semipermeable membrane is operated at a high pressure.

  The thickness of the separation functional layer is the shortest distance from the outer surface to the inner surface of the pleated structure. The standard deviation of the thickness of the separation functional layer is calculated from measured values at least 50 locations. The standard deviation of the thickness of the separation functional layer is preferably 2.0 nm or less. When the standard deviation is within this range, high boron removal performance can be obtained.

  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, 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. Says amine. For example, as a polyfunctional amine, phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene in which two amino groups are bonded to a benzene ring in any of the ortho-position, meta-position, and para-position, Aromatic polyfunctional amines such as 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine and 4-aminobenzylamine; aliphatic amines such as ethylenediamine and propylenediamine; -An alicyclic polyfunctional amine such as diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, 4-aminoethylpiperazine and the like can be mentioned. Among them, considering the selective separation property, permeability, and heat resistance of the membrane, the polyfunctional amine is an aromatic polyfunctional having 2 to 4 primary amino groups and / or secondary amino groups in one molecule. An amine is preferred. As such a polyfunctional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, m-phenylenediamine (hereinafter referred to as m-PDA) is preferably used from the viewpoint 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-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and the like. Examples of the bifunctional acid halide include aromatic bifunctional acid halides such as biphenyl dicarboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalene dicarboxylic acid chloride, adipoyl chloride, sebacoyl chloride, and the like. Examples thereof include alicyclic bifunctional acid halides such as aliphatic difunctional acid halides, cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, and tetrahydrofuran dicarboxylic 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. Of these, trimesic acid chloride is preferable from the viewpoint of availability and ease of handling. These polyfunctional acid halides may be used alone or in combination of two or more.

(1-2) Support Membrane The support membrane includes a base material and a porous support layer, has substantially no separation performance such as ions, and has a strength to a separation functional layer having separation performance substantially. Can be given.
The thickness of the support membrane affects the strength of the composite semipermeable membrane and the packing density when it is made into 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 300 μm, more preferably in the range of 50 to 250 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. .

[Porous support layer]
The porous support layer preferably contains the following materials as main components. As the material for the porous support layer, polysulfone, polyethersulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, homopolymers or copolymers, alone or blended. Can be used. Here, cellulose acetate, cellulose nitrate and the like are used as the cellulose polymer; polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and the like are 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 can be particularly preferably used because of its high chemical, mechanical and thermal stability and easy molding.
Specifically, as the material for the porous support layer, polysulfone composed of repeating units represented by the following chemical formula is preferable because the pore diameter can be easily controlled 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.
The porous support layer can be obtained, for example, by casting an N, N-dimethylformamide (hereinafter referred to as DMF) solution of the above polysulfone on a substrate to a certain thickness and wet coagulating it in water. It is done. By this method, it is possible to obtain a porous support layer in which most of the surface has fine pores having a diameter of 1 to 30 nm.
When the porous support layer contains polysulfone, the polysulfone content in the first layer and the polysulfone content in the second layer are both preferably 50% by weight or more. Moreover, it is preferable that the content rate of polysulfone is 50 weight% or more in the whole porous support layer.

  Moreover, it is preferable that the thickness of a porous support layer exists in the range of 10-200 micrometers, More preferably, it exists in the range of 20-100 micrometers. The thickness of the substrate is preferably in the range of 10 to 250 μm, more preferably in the range of 20 to 200 μm.

  The surface of the porous support layer (that is, the surface facing the separation functional layer) has a granular structure, but the higher the particle density, the higher the number density of protrusions in the separation functional layer and the greater the surface area of the separation functional layer. And it becomes a structure with excellent water permeability. This is considered to be due to the following reason.

  In the formation of the separation functional layer, the polyfunctional amine aqueous solution is in contact with the support membrane, and the polyfunctional amine aqueous solution is transferred from the inside of the porous support layer to the surface during polycondensation. The surface of the porous support layer functions as a reaction field for polycondensation, and the polyfunctional amine aqueous solution is supplied from the inside of the porous support layer to the reaction field, whereby the convex portion of the separation functional layer grows. When the number density of grains on the surface of the porous support layer as a reaction field is large, the number of growth points of the convex portions increases, and as a result, the number density of the convex portions increases. In general, a porous support layer having a high number density of grains on the surface is dense and has a small porosity and a small pore diameter.

  On the other hand, when the porosity of the porous support layer is high, the pore size is large, and the continuity is high, the monomer is uniformly and efficiently supplied to the reaction field, so that the thickness is uniform and the convex portion A separation functional layer having a large height is formed.

  Thus, the thickness uniformity and the height of the convex portions are determined by the supply amount and uniformity of the polyfunctional amine aqueous solution from the porous support layer, and the number density of the convex portions is determined by the surface structure. In the porous support layer, in order to increase the surface area of the separation functional layer by increasing the number density of the convex portions and to obtain high water permeability, the number density of the grains on the separation functional layer side portion of the porous support layer Is preferably increased. In order to make the thickness of the separation functional layer uniform, a structure having a high porosity having many highly continuous pores is preferable.

  As an example of such a structure, the porous support layer is positioned closer to the separation functional layer than the first layer for efficiently transferring the polyfunctional amine aqueous solution, and controls the number density of the convex portions. It is preferable to provide a second layer. In particular, the first layer is preferably in contact with the substrate, and the second layer is preferably located on the outermost layer of the porous support layer so as to be in contact with the separation functional layer.

  The first layer plays a role of transferring an aqueous polyfunctional amine solution 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. In particular, the pore diameter is preferably 0.1 μm or more and 1 μm or less.

  As described above, the second layer serves as a reaction field for polycondensation, and holds and releases the monomer, thereby supplying the monomer to the separation functional layer to be formed, and also serving as a starting point for the growth of the convex portion. Also fulfills.

  Here, the porous support layer having a high number density of grains on the surface can form convex portions having a high number density. However, since it is dense, the transfer rate of the monomer to the polycondensation field is small, and the convex portions to be formed are small. There is an inconvenience of non-uniformity. At this time, the above-mentioned first layer, which is a layer having continuous pores, is thinly laminated on the first layer as the second layer on the substrate side, thereby forming a porous support layer. Since the transfer rate of the monomer can be supplemented, a uniform separation function layer can be formed. Thus, in order to simultaneously control the uniformity and number density of the convex portions, it is preferable that the porous support layer includes a first layer and a second layer formed thereon.

  Furthermore, it is preferable that the interface of the layer contained in the porous support layer has a continuous structure. A continuous structure refers to a structure in which no skin layer is formed between layers. 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 between the layers, the permeation flow rate is drastically lowered because of the high resistance in the porous support layer.

[Base material]
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. A polyester polymer is preferable because an excellent support film can be obtained.

  The polyester polymer 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 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 particular, the base material is preferably made of a long-fiber nonwoven fabric composed of thermoplastic continuous filaments. Moreover, since continuous tension | tensile_strength is applied with respect to the film forming direction when forming a semipermeable membrane continuously, it is preferable to use the long-fiber nonwoven fabric which is more excellent in dimensional stability for a base material.

  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 semi-permeable membrane manufacturing process and the membrane element manufacturing process include a heating process, but a phenomenon occurs in which the porous support layer or the separation functional layer contracts due to the heating. In particular, the shrinkage is remarkable 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 measured as follows. First, 10 small piece samples are randomly collected from the nonwoven fabric. Next, the surface of the sample is photographed at 100 to 1000 times with a scanning electron microscope. In the photographed image, 10 samples are selected for each sample, and the angle when the longitudinal direction (longitudinal direction, film forming direction) of the nonwoven fabric is 0 ° is measured. That is, the angle is measured for a total of 100 fibers per nonwoven fabric. An average value is calculated from the angles of 100 fibers thus measured. The value obtained by rounding off the first decimal place of the obtained average value is the fiber orientation degree.

(1-3) Water production amount and boron removal rate The composite semipermeable membrane is composed of seawater having a NaCl concentration of 3.5 wt%, a boron concentration of 5 ppm, 25 ° C., and a pH of 6.5 at an operating pressure of 5.5 MPa for 24 hours. It is preferable that the amount of water produced after permeation is 1.00 m ³ / m ² / day or more and the boron removal rate is 85% or more.

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.

  By controlling the impregnation of the polymer solution into the substrate, a support film having a predetermined structure can be obtained. 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 The method of adjusting a viscosity by controlling a density | concentration is mentioned, These methods are also combinable.

  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 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.

  As a result of intensive studies by the present inventors, a porous support layer having a larger number density of grains on the surface is obtained as the polymer concentration (that is, solid content concentration) in the polymer solution is higher. It was found that the number density of the part was also increased. In order to realize a pleat structure that can withstand pressure fluctuations, in the porous support layer, at least the surface layer on the separation functional layer side is formed using a polymer solution having a solid content concentration that forms the following second layer. Is preferred.

  As described above, when the porous support layer has a multilayer structure including the first layer and the second layer, the composition of the polymer solution A that forms the first layer and the composition of the polymer solution B that forms the second layer And may be different from each other. “Different composition” means that at least one of the types of the polymer to be contained and its solid content concentration, the additive and its concentration, and the solvent are different.

  The solid content concentration a of the polymer solution A is preferably 12% by weight or more, and more preferably 13% by weight or more. When the solid content concentration a is 12% by weight or more, the communication hole is formed to be relatively small, so that a desired hole diameter is easily obtained.

The solid content concentration a is preferably 18% by weight or less, and more preferably 15% by weight or less. When the solid content concentration a is 18% by weight or less, the phase separation sufficiently proceeds before solidification of the polymer solution, so that a porous structure is easily obtained.

  The solid content concentration b of the polymer solution B forming the second layer is preferably 14% by weight or more, and more preferably 15% by weight or more. When the solid content concentration of the polymer solution B is 14% by weight or more, deformation of the porous structure is suppressed even when the operating pressure largely fluctuates. Since the second layer directly supports the separation functional layer, deformation of the second layer can cause damage to the separation functional layer.

  Further, the solid content concentration b is preferably 35% by weight or less, and more preferably 30% by weight or less. When the solid content concentration of the polymer solution B is 35% by weight or less, the surface pore diameter of the porous support layer is adjusted to such an extent that the monomer supply rate during formation of the separation functional layer does not become too small. Therefore, a convex portion having an appropriate height is formed when the separation functional layer is formed.

  It is preferable that the solid content concentration a and the solid content concentration b 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.

  The “solid content concentration” described above can be replaced with “polymer concentration”. When the polymer compound forming the porous support layer is polysulfone, the above-mentioned “solid content concentration” can be replaced with “polysulfone concentration”. The temperature of the polymer solution during application of the polymer solution is preferably within the range of 10 to 60 ° C., for example, if it is polysulfone. Within this range, the polymer solution does not precipitate, and the organic solvent solution containing the polymer compound is sufficiently impregnated between the fibers of the base material and then solidified. 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 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 the application of the polymer solution A, a high-density skin layer is formed on the surface of the first layer by the 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. In this state, the polymer solution B is coated on the polymer solution A.

  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 polymers contained in the polymer solution A and the polymer solution B may be the same or different from each other. 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.

  A good solvent is one that dissolves the polymer that forms the porous support layer. 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 for the polymer 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. And an aliphatic hydrocarbon such as polyethylene glycol, an aromatic hydrocarbon, an aliphatic alcohol, or a mixed solvent 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; water-soluble polymers such as polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol and polyacrylic acid or salts thereof; lithium chloride, sodium chloride, calcium chloride Inorganic salts such as lithium nitrate; formaldehyde, formamide and the like are exemplified, but 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 solid can be used as long as it does not dissolve the polymer. Further, the temperature of the coagulation bath is preferably -20 ° C to 100 ° C. More preferably, it is 10-30 degreeC. When the temperature is 100 ° C. or lower, the magnitude of vibration of the coagulation bath surface due to thermal motion can be suppressed, and the film surface can be formed smoothly. Further, when the temperature is −20 ° C. or higher, the solidification rate can be kept relatively high, and good film forming properties are realized.

  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 50 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. Conversely, if it is low, the cleaning effect is small.

(2-2) Formation of Separation Function Layer Next, as an example of the formation process of the separation function layer constituting the composite semipermeable membrane, description will be given by forming a layer containing polyamide as a main component (that is, a polyamide separation function layer). To do. In the process 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 and the organic solvent solution immiscible with water containing the polyfunctional acid halide. Doing includes forming a polyamide skeleton.

  The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1 wt% to 20 wt%, and more preferably in the range of 0.5 wt% to 15 wt%. . Within this range, sufficient water permeability and salt and boron removal performance can be obtained.

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

  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. Specifically, a method of coating a support membrane with a polyfunctional amine aqueous solution and a method of immersing the support membrane in a polyfunctional amine aqueous solution can be exemplified. 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. The portion where the droplets remain may become a defect after the formation of the composite semipermeable membrane, and this defect reduces the salt and boron removal performance of the composite semipermeable membrane. By sufficiently draining the liquid, generation of defects can be suppressed. 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 air by blowing an air current 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 can 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 liquid draining method, for example, a method of removing the excess organic solvent by flowing down naturally by holding the film in the vertical direction 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. Utilization of composite semipermeable membrane The composite semipermeable membrane manufactured in this way is combined with raw water flow path materials such as plastic nets, permeate flow path materials such as tricot, and a film for enhancing pressure resistance as required. The spiral semi-permeable membrane element can be formed by being wound around a cylindrical water collecting pipe having a large number of holes. 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 1.0 MPa or more and 10 MPa or less. The operating pressure is a so-called transmembrane pressure. As the feed water temperature increases, the salt removability decreases, but as it decreases, the membrane permeation flux also decreases. 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 composite 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 16% 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 is passed through a double slit die on a long fiber non-woven fabric (thread diameter: 1 dtex, thickness: about 90 μm, air permeability: 1.3 cc / cm ² / sec) made of polyethylene terephthalate fiber. The polymer solution A was cast at a thickness of 110 μm and the polymer solution B was cast at a thickness of 50 μm at the same time, immediately immersed in pure water at 25 ° C. and washed for 5 minutes to obtain a support membrane.

  The obtained support membrane was immersed in a 4.0 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 excess solution from the film, the film surface was held vertically for 1 minute to drain the liquid. 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)
A composite semipermeable membrane in Example 2 was obtained in the same manner as in Example 1 except that a DMF solution containing 20% by weight of polysulfone was used as the polymer solution B.

(Example 3)
A composite semipermeable membrane in Example 3 was obtained in the same manner as in Example 1 except that a DMF solution of 15% by weight of polysulfone was used as the polymer solution A and a DMF solution of 20% by weight of polysulfone was used as the polymer solution B. It was.

Example 4
A composite semipermeable membrane in Example 4 was obtained in the same manner as in Example 1 except that NMP was used as the solvent.

(Example 5)
In Example 1, in the same manner as in Example 1, except that a short fiber nonwoven fabric having a yarn diameter of 1 dtex, a thickness of about 90 μm, and an air permeability of 0.7 cc / cm ² / sec was used as the base material. A composite semipermeable membrane was obtained.

(Comparative Example 1)
A support membrane was obtained by the same procedure as in Example 1 except that only 13% by weight of polysulfone DMF solution was applied on the nonwoven fabric with a thickness of 160 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 Comparative Example 1 except that a 16% by weight polysulfone DMF solution was used as the polymer solution.

(Comparative Example 3)
A composite semipermeable membrane in Comparative Example 3 was obtained in the same manner as Comparative Example 1 except that a 13% by weight polysulfone NMP solution was used as the polymer solution.

(Comparative Example 4)
A composite semipermeable membrane in Comparative Example 4 was prepared in the same manner as in Example 1 except that a polymer sulfone 16 wt% DMF solution was used as the polymer solution A and a polysulfone 13 wt% DMF solution was used as the polymer solution B. Obtained.

(Comparative Example 5)
A composite semipermeable membrane in Comparative Example 5 was prepared in the same manner as in Example 1, except that a polymer sulfone 20 wt% polysulfone DMF solution was used as the polymer solution A, and a polysulfone 13 wt% DMF solution was used as the polymer solution B. Obtained.

(Comparative Example 6)
A DMF solution containing 13% by weight of polysulfone was applied on the nonwoven fabric to a thickness of 110 μm, and thereafter, a support membrane having a single porous support layer was obtained by the same procedure as in Comparative Example 1. On the porous support layer thus obtained, a DMF solution of 16% by weight of polysulfone was applied in a thickness of 50 μm, and a two-layer porous support layer was again formed through the same procedure as in Comparative Example 1. That is, the first layer and the second layer included in the porous support layer were applied and solidified sequentially, not simultaneously.
On the support membrane having the two porous support layers thus obtained, a separation functional layer was formed by the same procedure as in Example 1 to obtain a composite semipermeable membrane in Comparative Example 6.

<Measurement of the number density of protrusions, the average height of protrusions, and the standard deviation of the thickness of the separation functional layer>
The composite semipermeable membrane sample was embedded with an epoxy resin, stained with osmium tetroxide for easy 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 20,000 times. About the obtained cross-sectional photograph, the number of convex portions at a distance of 2.0 μm in width in the film surface direction of the support film was measured using a scale, and the 10-point average surface roughness was calculated as described above. Based on this 10-point average surface roughness, a portion having a height of 1/5 or more of the 10-point average surface roughness is defined as a convex portion, the number thereof is counted, and the average number density of the convex portions of the separation functional layer is calculated. Asked. Moreover, the height of all the convex parts in a cross-sectional photograph was measured with the scale, and while calculating | requiring the average height of a convex part, the standard deviation of the thickness in a separation function layer was calculated.

<Boron removal rate>
By supplying seawater having a NaCl concentration of 3.5 wt%, a boron concentration of 5 ppm, a temperature of 25 ° C., and a pH of 6.5 to the composite semipermeable membrane at an operating pressure of 5.5 MPa, 24 hours After performing the water treatment operation over a period of time, the boron removal rate was measured using the permeated water obtained at an operating pressure of 5.5 MPa.
That is, the boron concentration in the feed water and the permeated water was analyzed with an ICP emission analyzer (P-4010 manufactured by Hitachi, Ltd.) and obtained from the following equation.
Boron removal rate (%) = 100 × {1− (boron concentration in permeated water / boron concentration in feed water)}

<Membrane permeation flux>
The amount of permeated water obtained by the above filtration treatment for 24 hours was expressed as a membrane permeation flux (m ³ / m ² / day) with a water permeation amount per cubic meter (m ³ ) per day.
The results are shown in Table 1.

  As shown in Table 1, according to Examples 1 to 5 of the present invention, it can be seen that composite semipermeable membranes having both high boron removal performance and water permeability can be obtained.

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

DESCRIPTION OF SYMBOLS 1 Separation functional 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

Claims (10)

A substrate;
A porous support layer formed on the substrate;
A composite semipermeable membrane comprising a separation functional layer having a pleated structure formed on the porous support layer and having convex and concave portions continuously repeated,
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 at least 1/5 of the 10-point average surface roughness of the separation functional layer. A composite semipermeable membrane, wherein the average height of the convex portions having a height of 70 nm is 70 nm or more, and the standard deviation of the thickness of the separation functional layer in the cross section is 2.0 nm or less.   The composite semipermeable membrane according to claim 1, wherein an average height of the convex portions is 90 nm or more.   The composite semipermeable membrane according to claim 2, wherein the porous support layer has a multilayer structure of a first layer on the base material side and a second layer formed on the first layer.   The composite semipermeable membrane according to claim 3, 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 4, wherein the composite semipermeable membrane is formed.   The composite semipermeable membrane according to claim 5, wherein the polymer solution A and the polymer solution B have different compositions.   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. Item 7. The composite semipermeable membrane according to Item 6. The porous support layer contains polysulfone,
The composite semipermeable membrane according to any one of claims 3 to 7, wherein the polysulfone content in the first layer and the polysulfone content in the second layer are both 50 wt%.   The composite semipermeable membrane according to any one of claims 1 to 8, wherein the base material is a long-fiber nonwoven fabric containing polyester as a main component.   A sea water treatment method using the composite semipermeable membrane according to any one of claims 1 to 9 and treating seawater at an operation pressure of 4 MPa or more.