JP6702181B2 - Composite semipermeable membrane - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture, and particularly to a composite semipermeable membrane that maintains performance under high temperature and high pressure and has high water permeability.

  Most of the reverse osmosis membranes and nanofiltration membranes currently on the market are composite semipermeable membranes. In particular, a composite semipermeable membrane obtained by coating a supporting layer with a separation functional layer composed of a crosslinked polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide has a high permeability and a high separation selectivity. It is widely used as a film (Patent Document 1).

Japanese Patent Laid-Open No. 5-76740

  The inventors have found that when a conventional composite semipermeable membrane is operated under high temperature and high pressure, the water permeability decreases. An object of the present invention is to provide a composite semipermeable membrane that can maintain its performance even under high temperature and high pressure.

In order to achieve the above object, the present invention has the following configurations.
(1) A composite semipermeable membrane comprising a base material, a porous support layer located on the base material, and a separation functional layer located on the porous support layer, wherein the separation functional layer comprises: A thin film containing a cross-linked wholly aromatic polyamide as a main component, wherein the thin film has a pleated structure having a plurality of convex portions and concave portions, and 40% or more of the convex portions are in pure water at 25° C. The amount of deformation when the convex portion is pressed with a force of 5 nN is 2.5 nm or less, the intermediate value of the height of the convex portion is 100 nm or more, and the film thickness of the thin film on the convex portion is 20 nm or less. Is a composite semipermeable membrane.
(2) The composite semipermeable membrane as described in (1) above, wherein the number of the convex portions having a deformation amount of 2.5 nm or less when pressed by a force of 5 nN is 50% or more.
(3) The separation functional layer is a polyamide separation functional layer formed by a polycondensation reaction of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide, and the polyamide separation functional layer includes an amino group, a carboxy group and The composite semipermeable membrane according to the above (1) or (2), wherein the composite semipermeable membrane contains an amide group and x is 0.28 or less, where x is a molar ratio of amino group/amide group.
(4) The x+y is 0.80 or less, where x is the amino group/amide group molar ratio of the polyamide separation functional layer and y is the carboxy group/amide group molar ratio. Composite semipermeable membrane.

  In the composite semipermeable membrane of the present invention, the proportion of the convex portion having a small deformation amount in the convex portion is 40% or more, so that the deformation of the polyamide separation functional layer can be suppressed even under high temperature and high pressure. Further, when the median value of the heights of the protrusions is 100 nm or more, the surface area can be increased, and when the thickness of the separation functional layer of the protrusions is 20 nm or less, the resistance can be reduced and the water permeability can be increased. it can. This makes it possible to obtain a composite semipermeable membrane which maintains its performance even under high temperature and high pressure and has high water permeability.

FIG. 1 is a drawing schematically showing a method for measuring the height of the protrusions of the separation functional layer. FIG. 2 is a drawing schematically showing a method for measuring the amount of deformation of the convex portions of the separation functional layer.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but the description of the constituent elements described below is one example (representative example) of the embodiments of the present invention, and the present invention is as follows unless the gist thereof is exceeded. The content is not limited to.
Moreover, in this specification, the percentages and parts represented by "mass" are synonymous with the percentages and parts represented by "weight."

1. Composite semipermeable membrane The composite semipermeable membrane according to the present invention is located on the support membrane (porous support membrane) including a base material and a porous support layer located on the base material, and the porous support layer. And a separation functional layer. The separation functional layer has substantially separation performance, and the support film does not substantially have separation performance of ions and the like, and can give strength to the separation functional layer.

(1-1) Substrate Examples of the substrate include polyester-based polymers, polyamide-based polymers, polyolefin-based polymers, and mixtures and copolymers thereof. Among them, a polyester polymer cloth having high mechanical and thermal stability is particularly preferable. As the form of the cloth, a long fiber non-woven fabric, a short fiber non-woven fabric, or a woven or knitted fabric can be preferably used. Here, the long fiber nonwoven fabric refers to a nonwoven fabric having an average fiber length of 300 mm or more and an average fiber diameter of 3 to 30 μm.

The substrate preferably has an air flow rate of 0.5 cc/cm ² /sec or more and 5.0 cc/cm ² /sec. When the air permeability of the base material is within the above range, the polymer solution is impregnated into the base material, so that the adhesiveness between the base material and the porous support layer is improved, and the physical stability of the obtained porous support membrane is improved. You can improve your sex.

  The thickness of the substrate is preferably in the range of 10 to 200 μm, more preferably 30 to 120 μm. In the present specification, the thickness means an average value unless otherwise specified. Here, the average value represents an arithmetic mean value. That is, the thickness of the base material is obtained by calculating the average value of the thicknesses of 20 points measured at intervals of 20 μm in the direction orthogonal to the thickness direction (the surface direction of the film) in cross-section observation. The thickness of the base material can also be measured with a digital thickness gauge. As the digital thickness gauge, PEACOCK (registered trademark) from Ozaki Seisakusho Co., Ltd. can be used. When a digital thickness gauge is used, the thickness is measured at 20 points and the average value is calculated.

(1-2) Porous support layer In the present invention, the porous support layer is for giving strength to a separation functional layer having substantially no separation performance for ions and the like and having substantially separation performance. .. The size and distribution of the pores of the porous support layer are not particularly limited, for example, uniform and fine pores, or having gradually larger fine pores from the surface on the side where the separation functional layer is formed to the other surface, and A porous support layer in which the size of the fine pores on the surface on which the separation functional layer is formed is 0.1 nm or more and 100 nm or less is preferable, but the material used and its shape are not particularly limited.

The material of the porous support layer includes, for example, homopolymers or copolymers such as polysulfone, polyether sulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide alone or. It can be used by blending. Here, as the cellulose-based polymer, for example, cellulose acetate, cellulose nitrate or the like can be used, and as the vinyl polymer, for example, polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile or the like can be used. Of these, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferable. More preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone is mentioned.Furthermore, among these materials, polysulfone is high in chemical, mechanical and thermal stability and easy to mold. Generally available.
Specifically, it is preferable to use polysulfone having a repeating unit represented by the following chemical formula because the pore diameter of the porous support layer can be easily controlled and the dimensional stability is high. In the formula below, n represents the number of repeating units.

  The polysulfone preferably has a weight average molecular weight (Mw) of 10000 or more and 200000 or less when measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard substance, and more preferably It is 15,000 or more and 100,000 or less. When Mw is 10,000 or more, mechanical strength and heat resistance preferable as the porous support layer can be obtained. Further, when the Mw is 200,000 or less, the viscosity of the solution is in an appropriate range, and good moldability can be realized.

  For example, an N,N-dimethylformamide (hereinafter referred to as DMF) solution of polysulfone is cast on a densely woven polyester cloth or non-woven cloth to a certain thickness and wet-coagulated in water to form a solution. Thus, it is possible to obtain a porous support layer having most of the surface having fine pores having a diameter of several 10 nm or less.

  The thickness of the base material and the porous support layer affects the strength of the composite semipermeable membrane and the packing density when it is used as an element. In order to obtain sufficient mechanical strength and packing density, the total thickness of the base material and the porous support layer is preferably 30 μm or more and 300 μm or less, and more preferably 100 μm or more and 220 μm or less. The thickness of the porous support layer is preferably 20 μm or more and 100 μm or less. The thickness of the porous support layer can be obtained by calculating the average value of the thicknesses at 20 points measured at intervals of 20 μm in the direction orthogonal to the thickness direction (the surface direction of the film) by observing the cross section similarly to the substrate. The thickness of the porous support layer can also be measured with a digital thickness gauge. Since the thickness of the separation functional layer is much smaller than that of the porous support layer, the thickness of the composite semipermeable membrane can be regarded as the thickness of the substrate and the porous support layer. Therefore, the thickness of the porous support layer can be easily calculated by measuring the thickness of the composite semipermeable membrane with a digital thickness gauge and subtracting the thickness of the base material from the thickness of the composite semipermeable membrane. As the digital thickness gauge, PEACOCK (registered trademark) from Ozaki Seisakusho Co., Ltd. can be used. When a digital thickness gauge is used, the thickness is measured at 20 points and the average value is calculated.

  The porous support layer used in the present invention can also be selected from various commercially available materials such as "Millipore Filter VSWP" (trade name) manufactured by Millipore and "Ultra Filter UK10" (trade name) manufactured by Toyo Roshi Kaisha, Ltd. "Office of Saline Water Research and Development Progress Report" No. 359 (1968).

(1-3) Separation Functional Layer The separation functional layer has a thin film whose main component is polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide. In other words, the separation functional layer contains a crosslinked wholly aromatic polyamide as a main component. The main component means a component that accounts for 50% or more of the components of the separation functional layer. When the separation functional layer contains 50% or more of cross-linked wholly aromatic polyamide, high-performance membrane performance is easily exhibited.

  The cross-linked wholly aromatic polyamide can be formed by interfacial polycondensation of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide.

  Here, it is preferable that at least one of the polyfunctional aromatic amine and the polyfunctional aromatic acid halide contains a trifunctional or higher functional compound. The thickness of the separation functional layer is usually in the range of 0.01 to 1 μm, preferably 0.1 to 0.5 μm in order to obtain sufficient separability and water permeability. The separation functional layer in the present invention is hereinafter also referred to as a polyamide separation functional layer.

  A polyfunctional aromatic amine has two or more amino groups of at least one of a primary amino group and a secondary amino group in one molecule, and at least one of the amino groups is a primary amino group. It means an aromatic amine that is an amino group. For example, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, p-diaminopyridine and the like. Two amino groups are bound to an aromatic ring in any of the ortho, meta, or para positions, 1,3,5-triaminobenzene, 1,2,4-triamine Examples include polyfunctional aromatic amines such as aminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. Of these, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferable in consideration of the selective separation property and water permeability of the membrane, and m-phenylenediamine, m-phenylenediamine, and 1,3,5-triaminobenzene are preferable because they are easily available and easily handled. It is more preferable to use phenylenediamine (hereinafter, also referred to as m-PDA). These polyfunctional aromatic amines may be used alone or in combination of two or more.

  The polyfunctional aromatic acid halide refers to an aromatic acid halide having at least two carbonyl halide groups in one molecule. Examples of trifunctional acid halides include trimesic acid chloride, and examples of bifunctional acid halides include biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride. Can be mentioned. Considering the reactivity with the polyfunctional aromatic amine, the polyfunctional aromatic acid halide is preferably a polyfunctional aromatic acid chloride, and in consideration of the selective separability and heat resistance of the membrane, one molecule A polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups therein is preferable. Among them, trimesic acid chloride, terephthalic acid chloride, and isophthalic acid chloride are more preferably used from the viewpoint of easy availability and easy handling. These polyfunctional aromatic acid halides may be used alone or in combination of two or more kinds.

  Moreover, in the separation functional layer, the thin film forms a pleated structure having a plurality of concave portions and convex portions. More specifically, in the pleat structure, the concave portion and the convex portion are repeated.

The convex portion of the separation functional layer in the present invention means a convex portion having a height of ⅕ or more of 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. The observation magnification is preferably 10,000 to 100,000 times. In the obtained cross-sectional image, as shown in FIG. 1, the surface of the separation functional layer (indicated by reference numeral “1” in FIG. 1) appears as a curve having a pleated structure in which convex portions and concave portions are continuously repeated. .. About this curve, a roughness curve defined based on ISO4287:1997 is obtained. A cross-sectional image is extracted with a width of 2.0 μm in the direction of the average line of the roughness curve.
The average line is a straight line defined based on ISO4287:1997, and is drawn such 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. It is a 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 functional layer 1 are measured with the average line as a reference line. The height gradually decreases from the highest convex portion, and an average value is calculated for the absolute values of the heights H1 to H5 of the five convex portions up to the fifth height, and the depth gradually decreases from the deepest concave portion. The average value of the absolute values of the depths D1 to D5 of the five recesses up to the fifth depth is calculated, and the sum of the absolute values of the obtained two average values is calculated. The sum thus obtained is the 10-point average surface roughness.

As a result of diligent studies, the present inventors have found that when the amount of deformation of the convex portions of the separation functional layer measured in pure water is small, the deformation due to heat is small. Specifically, when the deformation amount of the convex portion is measured at the measurement temperature of 25° C. and 40° C., the convex portion having the deformation amount of 2.5 nm or less at the measurement temperature of 25° C. is higher than that of the convex portion exceeding 2.5 nm. It was found that the change in the amount of deformation was small when the measurement temperature was 40°C. Therefore, when the number of convex portions having a deformation amount of 2.5 nm or less at the measurement temperature of 25° C. was increased, the convex portions having a deformation amount of 2.5 nm or less were present at 40% or more of the total number of the convex portions to increase the high temperature. It was found that a composite semipermeable membrane that can maintain performance even under high pressure can be obtained.
Specifically, the separation functional layer preferably satisfies the following conditions. The surface of the separation functional layer is observed in pure water with an atomic force microscope (AFM), and three arbitrary areas within a 2 μm square area are selected. Ten convex portions included in these three regions are selected in each region. Furthermore, the number X of convex portions that show a deformation amount of 2.5 nm or less when one point in a circular region having a diameter of 100 nm centering on the vertex of the selected convex portion is pushed in with a force of 5 nN is counted, and the ratio (X/ 30) is required. When the ratio (X/30) is 40% or more, the desired effect of the present invention can be obtained, and the ratio (X/30) is preferably 50% or more, and 60% or more. Is more preferable.

The deformation amount (Deformation) of the convex portion can be measured in a tapping mode of an atomic force microscope (AFM). Specifically, as shown in FIG. 2, on the force curve with the tip-sample distance (Separation) on the horizontal axis and the load on the vertical axis, the point before the cantilever is brought close to the sample is point A, and the load is The distance between the CDs was defined as the amount of deformation, where B was the moment of standing, C was the point at which the load was 90% of the maximum load, and D was the maximum load point. The force curve used was that when the cantilever was brought close to the sample.
As the atomic force microscope, a Dimension Fast Scan manufactured by Bruker AXS can be used. It is possible to observe underwater by using the attached attachment. In addition, at this time, the shape of the probe of the cantilever used is a conical shape (pyramidal shape). Be sure to calibrate before using the cantilever. First, the cantilever warpage sensitivity (Deflection Sensitivity) is measured using a substance having sufficient hardness. A silicon wafer or sapphire can be used as the substance having sufficient hardness. Next, the spring constant of the cantilever is measured by thermal vibration (Thermal Tune). The accuracy of measurement is improved by performing the calibration.

  The height of the convex portion is preferably 100 nm or more. When the height of the convex portion is 100 nm or more, a large surface area of the separation functional layer can be secured and the effective membrane area becomes large, so that the water permeability is improved.

  Furthermore, the film thickness of the separation functional layer of the convex portion is 20 nm or less. Further, the thickness of the separation functional layer of the convex portion is preferably 10 nm or more. When the film thickness of the separation functional layer of the convex portion is 20 nm or less, the resistance when water permeates is reduced, and the water permeability is improved. If the thickness of the separation functional layer of the convex portion is less than 10 nm, it becomes difficult to obtain a practical removal rate.

  That is, the number of protrusions whose deformation amount is 2.5 nm or less when the protrusion apex is pushed in with 5 nN is 40% or more of the total number of protrusions, and the intermediate height value of the protrusions is 100 nm or more. Moreover, since the thickness of the separation functional layer of the convex portion is 20 nm or less, a composite semipermeable membrane that maintains performance even under high temperature and high pressure and has high water permeability is obtained.

The height intermediate value and the film thickness of the convex portion can be measured with a transmission electron microscope. First, a sample is embedded with a water-soluble polymer in order to prepare an ultrathin section for a transmission electron microscope (TEM). Any water-soluble polymer may be used as long as it can retain the shape of the sample, and for example, polyvinyl alcohol (PVA) or the like can be used. Next, in order to facilitate cross-sectional observation, it is stained with OsO ₄ and cut with an ultramicrotome to prepare an ultrathin section. A cross-sectional photograph is taken of the obtained ultrathin section using a TEM. The observation magnification may be appropriately determined depending on the film thickness of the separation functional layer. The height of the convex portion can be analyzed by reading a cross-sectional photograph into image analysis software. At this time, the height of the convex portion is a value measured for the convex portion having a height of ⅕ or more of the 10-point average surface roughness. The median height of the convex portions is measured as follows. When observing arbitrary 10 cross sections in the composite semipermeable membrane, the height of the convex portion, which is ⅕ or more of the above-mentioned 10-point average surface roughness, is measured in each cross section. Furthermore, the convex portion height intermediate value can be obtained by calculating the intermediate value based on the calculation results for the cross sections at 10 locations. Here, each cross section has a width of 2.0 μm in the direction of the average line of the roughness curve.

  Similarly, the film thickness of the separation functional layer of the convex portion can be analyzed by reading the cross-sectional photograph into the image analysis software. Five convex parts are selected, and the thickness of the convex separating layer is measured at 10 points for each convex from the range from the top of the convex height to 90%, and the arithmetic mean value of 50 points in total is measured. Ask for.

  The polyamide separation functional layer has an amide group derived from polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide, and an amino group and a carboxy group derived from unreacted functional groups. In addition to these, there are other functional groups possessed by the polyfunctional aromatic amine or the polyfunctional aromatic acid halide. Furthermore, new functional groups can be introduced by chemical treatment. By performing the chemical treatment, a functional group can be introduced into the polyamide separation functional layer, and the performance of the composite semipermeable membrane can be improved. Examples of the new functional group include an alkyl group, an alkenyl group, an alkynyl group, a halogen group, a hydroxyl group, an ether group, a thioether group, an ester group, an aldehyde group, a nitro group, a nitroso group, a nitrile group and an azo group. For example, a chlorine group can be introduced by treating with an aqueous solution of sodium hypochlorite. The halogen group can also be introduced by the Sandmeyer reaction via the formation of a diazonium salt. Furthermore, an azo group can be introduced by performing an azo coupling reaction via formation of a diazonium salt.

  In the present invention, in the case of further improving the acid resistance, in the polyamide separation functional layer, x is preferably 0.28 or less, and is 0.20 or less, where x is the amino group/amide group molar ratio. Is more preferable. When a polyamide having an amino group at the terminal comes into contact with an acidic aqueous solution, the amino group may be ionized. The ratio of the amino groups to be ionized is determined by the acidity of the contacted aqueous solution and the acid dissociation constant of the conjugate acid of the amino groups. It is considered that when the amount of ionized amino groups is large, Coulomb repulsion occurs and the higher-order structure of polyamide is destroyed, resulting in changes in water permeability and solute removal rate.

  It was also found that the total amount of amino groups and carboxy groups and the molar ratio of amide groups also correlate with acid resistance. When a polyamide is treated under strongly acidic conditions, the amide group is hydrolyzed to break the molecular chain, which may reduce the solute removal rate. However, a polyamide functional layer having a small proportion of carboxy groups and amino groups, which are terminal functional groups, and a large proportion of amide groups, has a high molecular weight and is highly crosslinked, so that the structure does not easily change even under strong acidic conditions, The solute removal rate is less likely to decrease. When x+y is 0.80 or less, where x is the amino group/amide group molar ratio and y is the carboxy group/amide group molar ratio, a solute that can withstand practical use even when treated under strongly acidic conditions The removal rate can be maintained.

Here, the molar ratio of the amino group, the carboxy group and the amide group can be determined by ¹³ C solid state NMR measurement of the separation functional layer. Specifically, after peeling the base material from the composite semipermeable membrane 5 m ² to obtain a polyamide separation functional layer and a support layer, the support layer is dissolved and removed with a solvent such as DMF or dichloromethane to form the polyamide separation functional layer. obtain. The obtained polyamide separation functional layer is measured by the DD/MAS- ¹³ C solid state NMR method, and each ratio is calculated from the comparison of the integrated value of the carbon peak of each functional group or the carbon peak to which each functional group is bound. be able to.

2. Method for Manufacturing Composite Semipermeable Membrane Next, a method for manufacturing the composite semipermeable membrane will be described.

(2-1) Outline The method for producing a composite semipermeable membrane includes at least a step of forming a separation functional layer on a membrane having a base material and a support layer. Further, the method for producing the composite semipermeable membrane may include a step of forming a support layer on the base material, a step of producing the base material, a step of performing a post-treatment after forming the separation functional layer, and the like.

(2-2) Separation Functional Layer Forming Step The separation functional layer forming step constituting the composite semipermeable membrane will be described. The step of forming the separation functional layer is
(A) contacting an aqueous solution containing a polyfunctional aromatic amine on the support layer,
(B) a step of contacting an organic solvent solution containing a polyfunctional aromatic acid halide with a support layer that is in contact with an aqueous solution containing a polyfunctional aromatic amine,
(C) heating the support layer in contact with an organic solvent solution containing a polyfunctional aromatic acid halide, and (d) draining the organic solvent solution after the step (c).
Have.

  In the step (a), the concentration of the polyfunctional aromatic amine in the polyfunctional aromatic amine aqueous solution is preferably in the range of 0.1% by mass or more and 12% by mass or less, more preferably 0.5% by mass or more and 8% by mass or more. It is within the range of mass% or less. When the concentration of the polyfunctional aromatic amine is within this range, sufficient solute removal properties and water permeability can be obtained. The polyfunctional aromatic amine aqueous solution may contain an organic solvent, an alkaline compound, an antioxidant or the like as long as it does not interfere with the reaction between the polyfunctional aromatic amine and the polyfunctional aromatic acid halide. .. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and if added, the interfacial polycondensation reaction may be performed efficiently.

  Moreover, since the polyfunctional aromatic amine is easily deteriorated by being oxidized, the yield of the reaction in the step (b) is improved by re-purifying the polyfunctional aromatic amine immediately before forming the polyfunctional aromatic amine aqueous solution. As a result, a film having high acid resistance can be obtained. For purification, a method such as recrystallization or sublimation purification can be used. The polyfunctional aromatic amine preferably has a purity of 99% or higher, more preferably 99.9% or higher.

  It is preferable that the polyfunctional aromatic amine aqueous solution contains a surfactant. As the surfactant, a linear alkyl sulfonic acid or a salt thereof is preferable, and examples thereof include hexane sulfonic acid, sodium hexane sulfonate, sodium octane sulfonate, and sodium decane sulfonate. The surfactant has the effects of improving the wettability of the surface of the supporting film and reducing the interfacial tension between the polyfunctional aromatic amine aqueous solution and the non-polar solvent. The effect can be obtained if the concentration of the surfactant is 0.1 equivalent or more with respect to the molar concentration of the polyfunctional aromatic amine.

  The contact with the polyfunctional aromatic amine aqueous solution is preferably carried out uniformly and continuously on the support layer. Specifically, for example, a method of coating the polyfunctional aromatic amine aqueous solution on the support layer and a method of immersing the support layer in the polyfunctional aromatic amine aqueous solution can be mentioned. In particular, it is preferable to apply the polyfunctional aromatic amine aqueous solution only to the support layer side, and a shower or a spray can be used for the application. The contact time between the porous support layer and the polyfunctional amine aqueous solution is preferably 1 second or more and 10 minutes or less, and more preferably 10 seconds or more and 3 minutes or less. When the polyfunctional aromatic amine aqueous solution is applied only to the support layer side, the contact time is preferably 1 second or longer and 1 minute or shorter, and more preferably 1 second or longer and 30 seconds or shorter.

  After the polyfunctional aromatic amine aqueous solution is brought into contact with the support layer, it 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 liquid droplets from becoming a film defect and deteriorating the film performance after the formation of the separation functional layer. As a method of draining, for example, as described in Japanese Patent Application Laid-Open No. 2-78428, the supporting membrane after contacting the aqueous solution of the polyfunctional aromatic amine is vertically held to allow the excess aqueous solution to flow naturally. It is possible to use, for example, a method of performing the above, or a method of blowing a stream of nitrogen or the like from an air nozzle to forcibly drain the liquid. Further, after draining, the film surface may be dried to partially remove the water content of the aqueous solution.

  In the step (b), the concentration of the polyfunctional aromatic acid halide in the organic solvent solution is preferably in the range of 0.01% by mass or more and 5.0% by mass or less, and 0.02% by mass or more and 2. More preferably, it is within the range of 0 mass% or less. This is because a sufficient reaction rate can be obtained with an amount of 0.01% by mass or more, and the occurrence of side reactions can be suppressed with an amount of 5.0% by mass or less.

  The organic solvent is preferably one that is immiscible with water, dissolves the polyfunctional acid halide and does not destroy the support film, and is inert to the polyfunctional amine compound and the polyfunctional acid halide. I wish I had it. Further, when the boiling point or the initial boiling point of the organic solvent is 100° C. or higher, it is easy to control the residual rate of the organic solvent, which is preferable. Preferred examples include hydrocarbon compounds such as n-nonane, n-decane, n-undecane, n-dodecane, isodecane and isododecane.

  Further, the water content in the organic solvent is preferably 100 ppm or less and 5 ppm or more, more preferably 50 ppm or less and 5 ppm or more, and further preferably 20 ppm or less and 5 ppm or more. The acid halide is hydrolyzed by water in an organic solvent to a carboxy group, which does not react with an amine. Moreover, since hydrolysis is promoted during heating, it is difficult to improve the molecular weight and the degree of crosslinking. When the water content is 100 ppm or less, the hydrolysis of the acid halide is suppressed, and the deformation amount when the projection is pushed in with a force of 5 nN is 2.5 nm or less and 40% or more. When the water content is 5 ppm or more, the diffusivity of the polyfunctional aromatic amine into the organic solvent is increased during the interfacial polymerization, and a fold structure having an intermediate height value of the protrusions of 100 nm or more can be formed.

  The water content in the organic solvent can be measured by the Karl Fischer method or a gas chromatograph. When measuring by the Karl Fischer method, a trace moisture measuring device manufactured by Mitsubishi Kasei Co., Ltd. can be used.

As a method of reducing the water content in the organic solvent, there is a method in which a desiccant is added to the organic solvent to absorb water before use. Examples of the desiccant include molecular sieve, aluminum oxide, magnesium oxide, silica gel, zinc chloride and the like.
As a method for increasing the water content in the organic solvent, there is a method in which pure water is put into the organic solvent and stirred before use. In addition, the water content can be easily controlled by adding the additive to the organic solvent. As the additive, one having a high affinity with an organic solvent and water is preferable, and examples thereof include acetone, ethanol and isopropyl alcohol.

  The method of contacting the support layer in contact with the polyfunctional aromatic amine compound aqueous solution of the organic solvent solution of the polyfunctional aromatic acid halide is the same as the method for coating the support layer of the polyfunctional aromatic amine aqueous solution. Good.

  In the step (c), the support layer brought into contact with the organic solvent solution of the polyfunctional aromatic acid halide is heated. Examples of the heating method include a hot-air oven or infrared irradiation, or a method of bringing a high-temperature object into contact with the base material side. For example, in the case of a hot air oven, it is preferable that the temperature be 80°C or higher and 120°C or lower. By heating at 80° C. or higher, it is possible to compensate for the decrease in reactivity due to the consumption of monomers in the interfacial polymerization reaction by the effect of accelerating the reaction by heat, and at the same time, increase the mobility of the monomer or oligomer. As a result, 40% or more of the protrusions have a deformation amount of 2.5 nm or less when the protrusions are pressed with a force of 5 nN, and a pleated structure having an intermediate height of the protrusions of 100 nm or more can be formed. .. Further, by heating at 120° C. or lower, it is possible to prevent the monomer concentration from excessively increasing due to concentration and excessive oligomer formation, and the separation functional layer thickness of the convex portion becomes 20 nm or less.

The heat treatment is preferably performed until the residual ratio of the organic solvent in the porous support layer before and after becomes 20% or more and 60% or less. Here, the residual ratio of the solvent is represented by the ratio of the mass of the support film after heating to the mass of the support film before heating. That is, the residual rate of the organic solvent is calculated from the mass of the porous support layer 100 cm ² before and after heating by the following formula.
Organic solvent residual rate (%)=(mass of film after heating)/(mass of film before heating)×100

  As a method of controlling the residual rate of the organic solvent, for example, it can be controlled by the oven temperature, the wind velocity on the film surface, and the heating time. When the residual ratio of the organic solvent is 60% or less, the convex portion is 5 nN due to the synergistic effect of promoting the interfacial polymerization reaction by heat and promoting the interfacial polymerization reaction by concentrating the polyfunctional aromatic acid halide during the interfacial polymerization. 40% or more of the convexes have a deformation amount of 2.5 nm or less when pressed by the force of. When the residual ratio of the organic solvent is 20% or more, the mobility of the oligomer molecules generated by the interfacial polymerization can be ensured, the decrease in the interfacial polymerization reaction rate can be suppressed, and the convex portion can be pressed with a force of 5 nN. 40% or more of the convexes have a deformation amount of 2.5 nm or less.

  In the step (d), the organic solvent solution after the reaction is removed by the draining step. The organic solvent can be removed by, for example, holding the film in a vertical direction to naturally remove excess organic solvent, removing the organic solvent by blowing air with a blower, or a mixed fluid of water and air. A method of removing excess organic solvent with (two fluids) can be used.

  After the step (d), it is preferable to add a step of performing a washing treatment with hot water in the range of 60°C to 90°C for 1 minute to 60 minutes.

  When the amino group/amide group molar ratio is reduced, it is more preferable to use a mixture of a hydrocarbon compound having 8 or less carbon atoms and a hydrocarbon compound having 9 or more carbon atoms. In this case, preferable examples of the hydrocarbon compound having 8 or less carbon atoms include n-hexane, n-heptane, n-octane and isooctane. Although the reason for this is not clear, the hydrocarbon compound having 8 or less carbon atoms easily diffuses the polyfunctional aromatic amine from the polyfunctional aromatic amine aqueous solution in the porous support layer to the organic solvent side, and thus the step (b) It is thought to accelerate the reaction of. Further, since the hydrocarbon compound having 8 or less carbon atoms has high volatility, it is possible to reduce the concentration of the polyfunctional aromatic amine and the polyfunctional aromatic acid halide in the organic solvent by vaporizing during the heating in the step (c). increase. It is considered that this can accelerate the interfacial polymerization reaction and reduce the amino group/amide group molar ratio. The mixing ratio of the hydrocarbon compound having 8 or less carbon atoms and the hydrocarbon compound having 9 or more carbon atoms is in the range of 30% by mass or more and 70% by mass or less of the hydrocarbon compound having 8 or less carbon atoms with respect to the sum of both. Is desirable. If the amount of the hydrocarbon compound having 8 or less carbon atoms is less than 30% by mass, the effect of reducing the molar ratio of amino group/amide group cannot be obtained, and if it exceeds 70% by mass, it is difficult to obtain the effect of promoting the reaction by heat. In some cases, the amount of deformation when the convex portion is pushed in by a force of 5 nN is 2.5 nm or less and the convex portion cannot be 40% or more.

3. Use of Composite Semipermeable Membrane The composite semipermeable membrane of the present invention is used for removing substances dissolved in a solvent, and is particularly suitable for removing solutes such as salts from water. Specifically, the composite semipermeable membrane of the present invention is suitable for water treatment. Water treatment includes production of drinking water or agricultural water from seawater, brackish water or water containing harmful substances; production of industrial ultrapure water; wastewater treatment; and recovery of valuables.

  The composite semipermeable membrane of the present invention is particularly suitable for desalination of high temperature brackish water and seawater. Specifically, the composite semipermeable membrane of the present invention can be used for water treatment under conditions where the temperature of raw water is 30°C or higher and the pressure is 1.0 MPa or higher. The temperature of raw water is preferably 50° C. or lower, and the pressure is preferably 7.0 MPa or lower.

  The composite semipermeable membrane of the present invention is suitably used as a spiral type composite semipermeable membrane element. Furthermore, a composite semipermeable membrane module in which these elements are connected in series or in parallel and housed in a pressure vessel can be used.

  The above-mentioned composite semipermeable membrane, its element, and module can be combined with a pump for supplying feed water to them, a device for pretreating the feed water, and the like to form a fluid separation device. By using this separator, the feed water can be separated into permeated water such as drinking water and concentrated water that has not permeated through the membrane to obtain water suitable for the purpose.

  As the feed water treated by the composite semipermeable membrane according to the present invention, a liquid mixture containing 500 mg/L or more and 100 g/L or less of TDS (Total Dissolved Solids: total dissolved solids) such as seawater, brackish water, and drainage water. Can be mentioned. Generally, TDS refers to the total amount of dissolved solids and is represented by "mass/volume" or "mass ratio". According to the definition, it can be calculated from the weight of the residue remaining when the solution filtered with a 0.45 micron filter is evaporated at a temperature of 39.5°C or higher and 40.5°C or lower, but more simply, Convert from practical salt (S).

  The higher the operating pressure of the fluid separation device, the higher the solute removal rate, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, the water to be treated is placed in the composite semipermeable membrane. The operating pressure for permeation is preferably 0.5 MPa or more and 10 MPa or less. Further, when the pH of the feed water becomes high, scales such as magnesium may be generated in the case of feed water having a high solute concentration such as seawater, and there is a concern that the membrane may deteriorate due to high pH operation. Driving is preferred.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

  The amount of deformation of the convex portion, the intermediate value of the height of the convex portion, the film thickness of the separation functional layer of the convex portion, the water content of the organic solvent, and the analysis of the functional group/composition in Comparative Examples and Examples were measured as follows.

<Deformation amount of convex part>
A composite semipermeable membrane wet with pure water was cut into 1 cm squares and fixed on a sample table with an adhesive so that the surface of the separation functional layer faces upward, to prepare a measurement sample. Next, the measurement sample was fixed on the measurement stage using a magnet, pure water was dropped on the separation functional layer, and then the surface was observed with an atomic force microscope (AFM). Ten points of the force curve of the convex portion were extracted from the obtained image, and the amount of deformation was analyzed. This operation was performed for 3 fields of view, and the deformation amount of 30 points in total was calculated. The specific measurement conditions are as follows.
-Device: Dimension FastScan manufactured by Bruker AXS
Scanning mode: underwater nanomechanical mapping Probe: Silicon cantilever (ScanAsyst-Fluid manufactured by Bruker AXS) The cantilever was calibrated before measurement.
・Maximum load: 5nN
・Scan range: 2μm×2μm
・Scanning speed: 0.5Hz
-Number of pixels: 256 x 256
・Measurement conditions: in pure water ・Measurement temperature: 25°C

<Thickness of the separation functional layer of the convex portion>
The composite semipermeable membrane was embedded in polyvinyl alcohol (PVA), stained with OsO ₄ , and cut with an ultramicrotome to prepare ultrathin sections. A cross-sectional photograph was taken of the obtained ultrathin section using a transmission electron microscope. A cross-sectional photograph taken by a transmission electron microscope is imported into the image analysis software Image J, 5 convex portions are selected, and 10 points are selected for each convex portion from the range from the upper part of the height of the convex portion to 90%. The film thickness of the separation functional layer of the convex portion was measured, and an arithmetic mean value of 50 points in total was obtained.

<Mid value of height of convex part>
The height of the convex portion can be measured by a transmission electron microscope, like the thickness of the functional layer for separating convex portions. The cross-sectional photograph obtained by the above-described method was read into image analysis software, the height of the convex portion and the depth of the concave portion at a distance of 2.0 μm were measured, 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 was measured for the convex portion having a height of ⅕ or more of the 10-point average surface roughness. Thereby, the median value of the height of the convex portions was calculated.

<Water content of organic solvent>
The water content of the organic solvent was measured 5 times using a trace moisture analyzer CA-05 type manufactured by Mitsubishi Kasei Co., Ltd., and the average value was obtained.

<Quantification of amino group, carboxy group, and amide group (functional group ratio)>
The base material was physically peeled off from the composite semipermeable membrane 5 m ² to recover the porous support layer and the separation functional layer. After being left to stand at 25° C. for 24 hours to dry, it was added little by little into a beaker containing dichloromethane and stirred to dissolve the polymer constituting the porous support layer. After that, the insoluble matter in the beaker was collected with a filter paper, and the insoluble matter was put again in a beaker containing dichloromethane and stirred to collect the insoluble matter in the beaker. This operation was repeated until the elution of the polymer forming the porous support layer in the dichloromethane solution could not be detected. The collected separation functional layer was dried with a vacuum dryer to remove residual dichloromethane. The obtained separation functional layer was freeze-pulverized to give a powdery sample, which was enclosed in a sample tube used for solid-state NMR measurement and subjected to ¹³ C solid-state NMR measurement by CP/MAS method and DD/MAS method. ^{For 13} C solid state NMR measurement, for example, CMX-300 manufactured by Chemagenetics can be used. An example of measurement conditions is shown below.
Reference substance: Polydimethylsiloxane (internal standard: 1.56ppm)
Sample rotation speed: 10.5 kHz
Pulse repetition time: 100 seconds From the obtained spectrum, peak division was performed for each peak derived from the carbon atom to which each functional group was bound, and the functional group ratio was quantified from the area of the divided peaks.
Quantification was carried out from the peak area near the carbon atom bonded to the amino group: 148 ppm.
It was quantified from the peak area near the carbon atom to which the carboxy group is bonded: 166 ppm.
Carbon atom to which amide group is bonded: Total aromatic carbon atom amount is quantified from the peak area of 100 to 145 ppm, and the amount of carbon atom to which amino group is bonded and carbon atom to which carboxy group is bonded are determined. It was calculated by calculating the difference.

<Membrane performance evaluation>
The performance of the composite semipermeable membrane was evaluated by the method described below.
(NaCl permeability)
Raw water for evaluation (NaCl concentration: 3.2%, boron concentration: about 5 ppm) adjusted to a temperature of 25° C. and a pH of 6.5 was supplied to the composite semipermeable membrane at an operating pressure of 5.5 MPa to carry out a membrane filtration treatment for 24 hours, and thereafter. The electric conductivity of the feed water and the permeated water of was measured by an electric conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. to obtain respective NaCl concentrations.
NaCl permeability (%)=100×(NaCI concentration in permeate/NaCI concentration in feed water)
(Membrane permeation flux)
In the test of the preceding paragraph, the membrane permeation flow rate (m ³ /m ² /day) was expressed by the membrane permeation rate of the supply water (evaluated raw water) per square meter of the membrane surface per day (cubic meter). ..
(Boron transmittance)
In the test of the previous section, the boron concentrations in the feed water and the permeated water were analyzed by an ICP emission spectrometer (P-4010 manufactured by Hitachi, Ltd.) and calculated from the following formula.
Boron permeability (%)=100×(boron concentration in permeate water/boron concentration in feed water)

<Durability evaluation under high temperature and high pressure>
Raw water for evaluation (NaCl concentration of 3.2%, boron concentration of about 5 ppm) adjusted to a temperature of 40° C. and a pH of 6.5 was supplied to the composite semipermeable membrane at an operating pressure of 5.5 MPa to perform membrane filtration treatment for 3 hours, and thereafter. The permeated water and the water quality of the supplied water were measured (3 hour value). The operation was continued, and after 120 hours, the water quality of the permeated water and the feed water was measured (120-hour value). The membrane permeation fluxes obtained by the 3 hour value and the 120 hour value were compared, and the change amount (120 hour value-3 hour value) was used as an index of durability.

<Acid resistance evaluation>
The composite semipermeable membrane was immersed in a sulfuric acid aqueous solution adjusted to pH 1 at 25° C. for 24 hours. Then, the composite semipermeable membrane was taken out from the sulfuric acid aqueous solution, thoroughly washed with pure water, and the boron permeability after the acid contact was measured. The amount of change in the boron permeability (boron permeability before acid contact) and the boron permeability after acid contact (after acid contact-before acid contact) measured in the film performance evaluation was used as an index of acid resistance.

<Reference example 1>
A 16.0 mass% DMF solution of polysulfone (PSf) was cast on a polyester non-woven fabric (air permeability of 2.0 cc/cm ² /sec) at a temperature of 25° C. to a thickness of 200 μm, and immediately immersed in pure water. A support film was prepared by leaving it for 5 minutes.

<Example 1>
According to the method described in International Publication No. 2011/105278, the supporting film obtained in Reference Example 1 was immersed in an aqueous solution containing 4% by mass of m-phenylenediamine (m-PDA) for 2 minutes to prepare the supporting film. Is slowly pulled up in the vertical direction, nitrogen is blown from the air nozzle to remove the excess aqueous solution from the surface of the supporting film, and then a 25°C undecane solution (water content 16 ppm) containing 0.12% by mass of trimesic acid chloride (TMC) is added. It was applied so that the surface was completely wet. Next, it is heated in an oven at 100°C until the residual rate of the organic solvent becomes 60%, and then, in order to remove the excess solution from the membrane, the membrane is made vertical and drained, and a blower is used to remove air at 20°C. Was sprayed on and dried. Finally, a composite semipermeable membrane was obtained by washing with pure water at 90°C. The resulting composite semipermeable membrane has a proportion of convex portions whose deformation amount is 2.5 nm or less when pressed with 5 nN, a median height of the convex portions, a separation functional layer thickness of the convex portions, 25° C., 40° C. Table 2 shows the performance of the film.

<Examples 2-9, Comparative Examples 1-11>
A composite semipermeable membrane was produced in the same manner as in Example 1 except that the organic solvent in which TMC was dissolved, the water content in the organic solvent, the temperature at the time of heat treatment, and the organic solvent residual ratio were changed to those shown in Table 1. The resulting composite semipermeable membrane has a proportion of convex portions whose deformation amount is 2.5 nm or less when pressed with 5 nN, a median height of the convex portions, a film thickness of a separation functional layer of the convex portions, 25° C., The membrane performance at 40° C. is shown in Table 2.

<Examples 10 to 12>
A composite semipermeable membrane was produced in the same manner as in Example 1 except that the aqueous solution of m-PDA contained 3% by mass of sodium hexanesulfonate and the heat treatment was changed to the conditions shown in Table 1. The resulting composite semipermeable membrane has a proportion of convex portions whose deformation amount is 2.5 nm or less when pressed with 5 nN, a median height of the convex portions, a separation functional layer thickness of the convex portions, 25° C., 40° C. Table 2 shows the performance of the film.

From the results of Table 2, the composite semipermeable membranes of Examples 1 to 12 in which the convex portion having a deformation amount of 2.5 nm or less when the convex portion was pressed with a force of 5 nN accounted for 40% or more were operated at 40°C. It was found that the amount of change in the membrane permeation flux at that time was as small as 0.25 or less. In addition, the intermediate value of the height of the protrusions is 100 nm or more, and the thickness of the separation functional layer of the protrusions is 20 nm or less, so that the evaluation at 25° C. is 0.60 (m ³ /m ² /day) or more. It was found to have high water permeability.

<Examples 13 to 18, Comparative Examples 12 to 13>
A composite semipermeable membrane was produced in the same manner as in Example 5 except that the solvent for dissolving TMC, the water content in the organic solvent, and the residual ratio of the organic solvent were changed to those shown in Table 3. The resulting composite semipermeable membrane has a proportion of convex portions whose deformation amount is 2.5 nm or less when pressed with 5 nN, a median height of the convex portions, a separation functional layer thickness of the convex portions, 25° C., 40° C. The film performance, the functional group ratio, and the performance after the acid resistance test are shown in Table 4.

  From the results of Table 4, as shown in Examples 13 to 18, when the amino group/amide group molar ratio of the separation functional layer was 0.28 or less, the amount of change in boron transmittance after acid contact was It was found that a composite semipermeable membrane that is small and has high acid resistance can be obtained.

  Although the present invention has been described in detail and with reference to particular embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on the Japanese patent application filed on February 27, 2015 (Japanese Patent Application No. 2015-038121) and the Japanese patent application filed on March 31, 2015 (Japanese Patent Application No. 2005-072326), the contents of which are as follows. Incorporated here by reference.

1 Separation Functional Layers H1, H2, H3, H4, H5 Height of Convex Part in Fold Structure of Separation Functional Layer D1, D2, D3, D4, D5 Depth of Recess in Fold Structure of Separation Functional Layer

Claims (4)

A composite semipermeable membrane comprising a base material, a porous support layer located on the base material, and a separation functional layer located on the porous support layer,
The separation functional layer has a thin film containing a cross-linked wholly aromatic polyamide as a main component,
The thin film has a pleated structure including a plurality of convex portions and concave portions,
40% or more of the protrusions have a deformation amount of 2.5 nm or less when the protrusions are pressed with a force of 5 nN in pure water at 25° C.,
And the intermediate value of the height of the convex portion is 100 nm or more,
Moreover, a composite semipermeable membrane in which the thickness of the thin film in the convex portion is 20 nm or less.   The composite semipermeable membrane according to claim 1, wherein the number of the convex portions having a deformation amount of 2.5 nm or less when pressed by a force of 5 nN is 50% or more. The separation functional layer is a polyamide separation functional layer formed by a polycondensation reaction of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide,
The composite half according to claim 1 or 2, wherein the polyamide separation functional layer contains an amino group, a carboxy group and an amide group, and x is 0.28 or less, where x is a molar ratio of amino group/amide group. Membrane.   The composite semipermeable membrane according to claim 3, wherein x+y is 0.80 or less, where x is the amino group/amide group molar ratio and y is the carboxy group/amide group molar ratio of the polyamide separation functional layer. .

Images