JP7342528B2 - Composite semipermeable membrane and method for manufacturing composite semipermeable membrane - Google Patents

Description

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

Regarding the separation of mixtures, there are various techniques for removing substances (e.g., salts) dissolved in a solvent (e.g., water), but in recent years, the use of membrane separation methods has expanded as a process for saving energy and resources. are doing.

Membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. It is used to obtain water, produce industrial ultrapure water, treat wastewater, recover valuable materials, etc.

Most of the reverse osmosis membranes and nanofiltration membranes currently on the market are composite semipermeable membranes; some have a gel layer and an active layer made of cross-linked polymers on a microporous support membrane, and others have a gel layer and an active layer made of crosslinked polymers on a microporous support membrane. There are two types: one has an active layer made by polycondensing monomers, and the other has an active layer.

Among them, a composite semipermeable membrane obtained by coating a porous support membrane with a separation functional layer made of a crosslinked polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide (Patent Document 1) is widely used as a separation membrane with high water permeability and removability.

Japanese Patent Application Publication No. 2001-79372

However, there is a growing need for energy saving during membrane operation, and the water permeability of composite semipermeable membranes needs to be further increased compared to conventional membranes. On the other hand, there is a problem in that when the water permeability of the membrane is increased, the removability is decreased accordingly.

The present invention takes the following configuration in order to significantly improve the water permeability while maintaining the removability of the membrane.
[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,
The separation functional layer contains a polyamide formed by interfacial polycondensation of an aliphatic amine and an aromatic amine with a polyfunctional acid halide,
A composite semipermeable membrane in which an amount A of hydrogen bonded to aromatic ring carbon and an amount B of hydrogen bonded to non-aromatic ring carbon constituting the polyamide satisfy the following formula.
0.015≦B/(A+B)≦0.15
[2] The separation functional layer has a pleated structure, and the median height of the convex portions in the pleated structure is 80 nm or more,
The composite semipermeable membrane according to [1], wherein the median thickness of the convex portions in the pleated structure is 8 nm or more and 15 nm or less.
[3] A method for producing 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 method comprising:
comprising a step of forming a separation functional layer on the porous support layer,
The process includes:

The polyfunctional amine contained in the polyfunctional amine aqueous solution is an aliphatic amine and an aromatic amine,
The amount of aliphatic amine and aromatic amine contained in the polyfunctional amine aqueous solution is
0.01≦aliphatic amine [mol]/(aromatic amine + aliphatic amine) [mol]<0.1
A method for manufacturing a composite semipermeable membrane that satisfies the following.
[4] The method for producing a composite semipermeable membrane according to [3], wherein the aliphatic amine is a piperazine derivative.
[5] The method for producing a composite semipermeable membrane according to [3] or [4], wherein the aromatic amine is m-phenylenediamine.

In the composite semipermeable membrane of the present invention, the amount of hydrogen A bonded to the aromatic ring carbon constituting the polyamide, which is the main component of the separation functional layer, and the amount B of hydrogen bonded to the non-aromatic ring carbon are 0.015≦B/(A+B )≦0.15, a pleat structure suitable for achieving both high water permeability and a practical removal rate can be obtained.

1. Composite Semipermeable Membrane (1-1) Microporous Support Membrane In the present invention, the microporous support membrane does not substantially have separation performance for ions, etc., but has a separation function layer described below that has substantial separation performance. It is meant to give strength. The size and distribution of the pores in the microporous support membrane are not particularly limited; In addition, a microporous support film having a microporous size of 0.1 nm or more and 100 nm or less on the surface on which the separation functional layer is formed is preferable.

In the present invention, the microporous support membrane is composed of a base material and a porous support formed thereon.

(1-1-1) Substrate The above-mentioned substrate is exemplified by a fabric whose main component is at least one selected from polyester and aromatic polyamide.

As the fabric used for the base material, long fiber nonwoven fabric or short fiber nonwoven fabric can be preferably used. When a high-molecular polymer solution is cast onto the base material, it may bleed through due to excessive penetration, the base material may peel from the porous support, or even the base material may become fluffy. Excellent film forming properties are required that do not cause defects such as non-uniformity or pinholes in the film. Therefore, a long fiber nonwoven fabric can be more preferably used as the base material.

Examples of the long-fiber nonwoven fabric include long-fiber nonwoven fabrics made of continuous thermoplastic filaments. Since the base material is made of a long fiber nonwoven fabric, it is possible to suppress nonuniformity or film defects during polymer solution casting caused by fluffing, which occur when a short fiber nonwoven fabric is used. Furthermore, in the process of continuously forming a composite semipermeable membrane, since tension is applied to the base material in the film forming direction, it is preferable to use a long fiber nonwoven fabric with excellent dimensional stability as the base material.

The air permeability of the base material is preferably 2.0 cc/cm ² /sec or more. When the air permeability is within this range, the amount of water permeated through the composite semipermeable membrane will be high. This is a process to form a microporous support membrane, and when a high molecular weight polymer is cast onto a base material and immersed in a coagulation bath, the rate of non-solvent replacement from the base material side increases, resulting in porosity. This is thought to be because the internal structure of the support changes, which affects the amount of monomer retained or the diffusion rate in the subsequent step of forming a separation functional layer.

Note that the air permeability can be measured using a Frazier type tester based on JIS L1096 (2010). For example, a base material is cut out to a size of 200 mm x 200 mm and used as a sample. This sample was attached to a Frazier type tester, and the suction fan and air hole were adjusted so that the pressure on the inclined barometer was 125 Pa. Based on the pressure indicated by the vertical barometer and the type of air hole used, The amount of air passing through the material, that is, the air permeability, can be calculated. As the Frazier type tester, KES-F8-AP1 manufactured by Kato Tech Co., Ltd., etc. can be used.

Further, the thickness of the base material is preferably in the range of 10 μm or more and 200 μm or less, more preferably 30 μm or more and 120 μm or less.

(1-1-2) Porous support The porous support in the present invention is located on the above-mentioned base material.

Porous support materials include homopolymers or copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide, either singly or in a blend. can be used.

Here, examples of the cellulose polymer include cellulose acetate and cellulose nitrate, and examples of the vinyl polymer include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile.

Among these, homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, and polyphenylene sulfide sulfone are preferred. Polysulfone, cellulose acetate, polyvinyl chloride, or a mixture thereof is more preferably used, and polysulfone, which has high chemical, mechanical, and thermal stability, is particularly preferably used.

Further, the thickness of the porous support is preferably within the range of 10 to 200 μm, more preferably within the range of 20 to 100 μm. When the thickness of the porous support is 10 μm or more, good pressure resistance can be obtained, and a uniform support membrane without defects can be obtained. can show good salt removal performance. When the thickness of the porous support is 200 μm or less, the amount of unreacted substances remaining during production does not increase, and it is possible to prevent a decrease in chemical resistance due to a decrease in the amount of permeated water.

The thickness of the microporous support membrane formed by forming the porous support on the base material influences the strength of the composite semipermeable membrane and the packing density when it is used as an element. In order for the composite semipermeable membrane of the present invention to obtain sufficient mechanical strength and packing density, the thickness of the microporous support membrane (total of the base material and porous support membrane) is within the range of 30 to 300 μm. It is preferably within the range of 50 to 250 μm.

The morphology of the microporous support membrane can be observed using a scanning electron microscope, a transmission electron microscope, an atomic microscope, or the like. For example, when observing with a scanning electron microscope, the porous support is peeled off from the base material and then cut using a freeze-fracture method to obtain a sample for cross-sectional observation. The sample is thinly coated with platinum or platinum-palladium or ruthenium tetrachloride, preferably ruthenium tetrachloride, and observed under a high-resolution field emission scanning electron microscope (UHR-FE-SEM) at an accelerating voltage of 3 to 6 kV. As a high-resolution field emission scanning electron microscope, a Hitachi S-900 model electron microscope or the like can be used.

The microporous support membrane used in the present invention may be selected from various commercially available materials such as "Millipore Filter VSWP" (trade name) manufactured by Millipore Corporation or "Ultra Filter UK10" (trade name) manufactured by Toyo Roshi Co., Ltd. Yes, but “Office of Saline Water Research and Development Progress Report” No. 359 (1968).

The thickness of the base material, porous support, and composite semipermeable membrane can be measured using a digital thickness gauge. Furthermore, since the thickness of the separation functional layer described later is very thin compared to the microporous support membrane, the thickness of the composite semipermeable membrane can also be regarded as the thickness of the microporous support membrane. Therefore, the thickness of the porous support 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 a digital thickness gauge, PEACOCK manufactured by Ozaki Seisakusho Co., Ltd., etc. can be used. When using a digital thickness gauge, the thickness is measured at 20 locations and the average value is calculated.

Note that the thicknesses of the base material, porous support, and composite semipermeable membrane may be measured using the above-mentioned microscope. The thickness is determined by measuring the thickness of one sample from electron micrographs of cross-sectional observations at five arbitrary locations and calculating the average value. Note that the thickness and pore diameter in the present invention mean average values.

(1-2) Separation Functional Layer In the composite semipermeable membrane of the present invention, it is the separation function layer that substantially has the ability to separate ions and the like. The separation functional layer forms a pleated structure in which concave portions and convex portions are repeated. The higher the convex portions, the larger the surface area, which increases the effective membrane area and improves water permeability.

In the present invention, the median height of the convex portions of the separation functional layer is 80 nm or more, preferably 90 nm or more. Further, the median height of the convex portions of the separation functional layer is preferably 1000 nm or less, more preferably 800 nm or less. When the median height of the convex portions is 80 m or more, a composite semipermeable membrane with sufficient water permeability can be easily obtained. Further, since the median height of the convex portions is 1000 nm or less, stable membrane performance can be obtained without crushing the convex portions even when the composite semipermeable membrane is operated and used at high pressure.

Further, in the present invention, the median thickness of the convex portions of the separation functional layer is 15 nm or less, preferably 13 nm or less. Further, the intermediate value of the thickness of the convex portion is preferably 8 nm or more. When the median thickness of the protrusions is 15 nm, a composite semipermeable membrane with sufficient water permeability can be easily obtained, and when the median thickness of the protrusions is 8 nm or more, it is possible to easily obtain a composite semipermeable membrane with sufficient water permeability. A practical salt removal rate and physical durability against operating pressure can be maintained.

Here, the convex portion of the separation functional layer in the present invention refers to a convex portion having a height of one-fifth 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 in the direction perpendicular to the membrane surface is observed using an electron microscope at the following magnification. In the obtained cross-sectional image, the surface of the separation functional layer (indicated by the symbol "1" in FIG. 1) appears as a curved line with a pleated structure in which convex portions and concave portions are continuously repeated. For this curve, a roughness curve defined based on ISO4287:1997 is determined. A cross-sectional image with a width of 2.0 μm is extracted in the direction of the average line of the roughness curve (FIG. 1).

Note that the average line is a straight line defined based on ISO4287:1997, and is drawn so that the total area of the area 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 sampled image having a width of 2.0 μm, the height of the convex portion and the depth of the concave portion in the separation functional layer are measured using the average line as a reference line. The average value is calculated for the absolute values of the heights H1 to H5 of the five convex portions, which gradually decrease in height from the highest convex portion to the fifth height, and the depth gradually decreases from the deepest concave portion. Then, 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 then the sum of the absolute values of the two obtained average values is calculated. The sum obtained in this way is the 10-point average surface roughness.

Then, the intermediate value of the height of the convex portion can be measured using a transmission electron microscope.

First, in order to prepare ultrathin sections for transmission electron microscopy (TEM), a sample is embedded in a water-soluble polymer. Any water-soluble polymer may be used as long as it can maintain the shape of the sample, and for example, PVA or the like can be used. Next, to facilitate cross-sectional observation, it is stained with OsO ₄ and cut with an ultramicrotome to prepare ultrathin sections. A cross-sectional photograph of the obtained ultra-thin section is taken using a TEM. The height of the convex portion can be measured directly by reading a cross-sectional photograph into image analysis software and analyzing it, or by using a scale. The height of the convex portion is a value measured for a convex portion having a height of one-fifth or more of the 10-point average surface roughness.

The intermediate value of the height of the convex portion is measured as follows. In the composite semipermeable membrane, when cross sections at ten arbitrary locations are observed, the height of the convex portions, which is one-fifth or more of the above-mentioned 10-point average surface roughness, is measured in each cross section. Furthermore, the intermediate value of the height of the convex portion can be determined 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.

The intermediate value of the thickness of the convex portion is calculated from measurements of the shortest distance from the outer surface to the inner surface of the pleat structure at at least 50 locations. Calculation is performed by directly measuring a TEM cross-sectional photograph with a magnification of 20,000 to 100,000 times using a scale.

The separation functional layer in the present invention contains a thin film containing polyamide as a main component. The polyamide constituting the separation functional layer can be formed, for example, by an interfacial polycondensation reaction between 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.

Here, a 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. Refers to a certain amine.

In the polyamide separation functional layer of the present invention, the amount A of hydrogen bonded to carbon atoms in an aromatic ring and the amount B bonded to carbon atoms in a non-aromatic ring satisfy the following formula.
0.015≦B/(A+B)≦0.15
During interfacial polycondensation, the presence of the non-aromatic ring carbon can make the polycondensation reaction rate mild due to electronic and steric factors.

In particular, in a polyamide separation functional layer that moderately reduces the polycondensation reaction rate and has an amount A of hydrogen bonded to aromatic ring carbons and an amount B of hydrogen bonded to non-aromatic ring carbons within the above range, the convex portions improve the water permeability of the membrane. While it continues to grow to a height suitable for sufficient expression, swelling due to reactions inside the convex portion is suppressed, resulting in a thinner film, which maintains practical removability while maintaining extremely high film removability. It was found that the membrane exhibits high water permeability.

The amount A of hydrogen bonded to carbon atoms in the aromatic ring and the amount B bonded to carbon atoms in the non-aromatic ring are determined, for example, as follows.

First, the base material is physically peeled off from the composite semipermeable membrane, and the separation functional layer is extracted using a solvent that can dissolve the support layer, such as dichloromethane. Add 2 mL of a 6N or higher aqueous sodium hydroxide solution to 50 mg of the obtained separation functional layer, place in a pressure-resistant container, and heat at 120°C for 1 hour or more. The resulting solution is made strongly acidic using hydrochloric acid or the like, then filtered, and the filtrate is dried and dissolved in deuterated chloroform and subjected to ¹ H NMR measurement. In the obtained spectrum, the peak integrated value of the chemical shift of 6 to 9.5 ppm is defined as the amount A of hydrogen bonded to the aromatic ring carbon, and the peak integrated value of the chemical shift of 0.7 to 4 ppm is defined as the amount B of hydrogen bonded to the non-aromatic ring carbon.

The polyfunctional amines constituting the polyamide in the present invention include aliphatic amines and aromatic amines, respectively. Examples of aliphatic amines include ethylenediamine, propylenediamine, piperazine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane and derivatives thereof, but in particular Piperazine derivatives having a substituent at one or more of the 2-, 3-, 5-, and 6-positions of piperazine are particularly preferred for improving the performance of the composite semipermeable membrane.

Examples of aromatic amines include phenylene diamine, xylylene diamine, 1,3,5-triaminobenzene, in which two amino groups are bonded to the benzene ring at either the ortho, meta, or para positions; Examples include 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, and 4-aminobenzylamine. Considering this, it is preferable to use an aromatic polyfunctional amine having 2 to 4 primary amino groups and/or secondary amino groups in one molecule. As such polyfunctional aromatic amines, for example, m-phenylenediamine (hereinafter referred to as m-PDA), p-phenylenediamine, 1,3,5-triaminobenzene, etc. are preferably used. Among these, it is more preferable to use m-PDA because of its ease of availability and handling.

The polyfunctional acid halide refers to an acid halide having at least two halogenated carbonyl groups in one molecule. For example, examples of the trifunctional acid halide include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, and 1,2,4-cyclobutanetricarboxylic acid trichloride.

Examples of difunctional acid halides include aromatic difunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalenedicarboxylic acid chloride, adipoyl chloride, and sebacoyl chloride. Examples include aliphatic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride, and tetrahydrofurandicarboxylic acid dichloride.

Considering the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride, and considering the selective separation property and heat resistance of the membrane, it is preferable that the polyfunctional acid halide contains 2 A polyfunctional aromatic acid chloride having ~4 carbonyl chloride groups is preferred. Among these, it is more preferable to use trimesic acid chloride from the viewpoint of ease of availability or handling. These polyfunctional acid halides may be used alone or in combination of two or more.

2. Method for manufacturing a composite semipermeable membrane Next, a method for manufacturing a composite semipermeable membrane of the present invention will be described.

(2-1) Support film formation process The support film formation process includes a process of applying a polymer solution to a base material and a process of immersing the base material coated with the polymer solution in a coagulation bath to solidify the polymer. including.

In the step of applying the polymer solution to the substrate, the polymer solution is prepared by dissolving a polymer, which is a component of the porous support layer, in a good solvent for the polymer.

When polysulfone is used as the polymer, the temperature of the polymer solution during application of the polymer solution is preferably 10° C. or more and 60° C. or less. If the temperature of the polymer solution is within this range, the polymer will not precipitate, and the polymer solution will solidify after sufficiently impregnating between the fibers of the base material. As a result, the porous support layer is firmly bonded to the base material due to the anchor effect, and a good support film can be obtained. Note that the preferred temperature range of the polymer solution can be adjusted as appropriate depending on the type of polymer used, the desired solution viscosity, and the like.

The time from when the polymer solution is applied to the substrate until it is immersed in the coagulation bath is preferably 0.1 seconds or more and 5 seconds or less. If the time until immersion in the coagulation bath is within this range, the organic solvent solution containing the polymer will sufficiently impregnate between the fibers of the base material and then solidify. Note that the preferred range of time until immersion in the coagulation bath can be adjusted as appropriate depending on the type of polymer solution used, the desired solution viscosity, and the like.

Water is usually used as the coagulation bath, but any coagulation bath may be used as long as it does not dissolve the polymer that is a component of the porous support layer. Depending on the composition of the coagulation bath, the morphology of the support membrane obtained changes, and thereby the composite semipermeable membrane obtained also changes. The temperature of the coagulation bath is preferably -20°C or more and 100°C or less, more preferably 10°C or more and 50°C or less. If the temperature of the coagulation bath is within this range, the surface of the coagulation bath will not vibrate violently due to thermal motion, and the smoothness of the film surface after film formation will be maintained. Moreover, if the temperature of the coagulation bath is within this range, the coagulation rate will be appropriate and the film forming property will be good.

Next, the support membrane thus obtained is washed with hot water to remove the solvent remaining in the membrane. The temperature of the hot water at this time is preferably 40°C or more and 100°C or less, more preferably 60°C or more and 95°C or less. If the temperature of the hot water is within this range, the degree of shrinkage of the support membrane will not increase and the amount of permeated water will be good. Further, if the temperature of the hot water is within this range, the cleaning effect will be sufficient.

(2-2) Formation step of separation functional layer The separation functional layer constituting the semipermeable membrane can be formed using, for example, an aqueous solution containing the above-mentioned polyfunctional amine and a water-immiscible material containing a polyfunctional acid halide. The skeleton can be formed by performing interfacial polycondensation on the surface of the microporous support membrane using an organic solvent solution.

Here, the concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably such that the total amount of aliphatic amine and aromatic amine is within the range of 0.1 to 10% by weight, more preferably within the range of 0.5 to 5.0% by weight. be. By setting the concentration of the polyfunctional amine within this range, the reaction can proceed appropriately, while ensuring sufficient water permeability without making the separation functional layer excessively thick. Further, the ratio of aliphatic amine to aromatic amine is preferably such that the ratio of aliphatic amine [mol]/(aromatic amine + aliphatic amine) [mol] satisfies 0.01 or more and less than 0.1. If the ratio is less than 0.01, it is insufficient to significantly improve the water permeability of the membrane, and if it is more than 0.1, the height of the convex portion of the separation functional layer becomes smaller, which will conversely reduce the water permeability of the membrane. This is because it works in the direction of decreasing.

The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, etc. as long as they do 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 surface of the microporous support membrane and reducing the interfacial tension between the polyfunctional amine aqueous solution and the organic solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and by adding the organic solvent, the interfacial polycondensation reaction may be carried out efficiently.

In order to perform interfacial polycondensation on the microporous support membrane, first, the above-mentioned polyfunctional amine aqueous solution is brought into contact with the microporous support membrane. The contact is preferably carried out uniformly and continuously on the surface of the microporous support membrane. Specifically, examples include a method of coating a microporous support membrane with a polyfunctional amine aqueous solution and a method of immersing a microporous support membrane in a polyfunctional amine aqueous solution. The contact time between the microporous support membrane and the polyfunctional amine aqueous solution is preferably within the range of 1 second to 10 minutes, more preferably within the range of 10 seconds to 3 minutes.

After the polyfunctional amine aqueous solution is brought into contact with the microporous support membrane, it is preferable to drain the solution sufficiently so that no droplets remain on the membrane. Since no droplets that cause film defects remain after the film is formed, the film performance is less likely to deteriorate. As a method of draining the liquid, for example, as described in JP-A-2-78428, the microporous support membrane after contact with the polyfunctional amine aqueous solution is gripped vertically and the excess aqueous solution is allowed to flow down by gravity. method, or a method of forcibly draining the liquid by blowing nitrogen or other air from an air nozzle. Further, after draining, the membrane surface can be dried to remove part of the water in the aqueous solution.

Next, the microporous support membrane that has been contacted with the polyfunctional amine aqueous solution is brought into contact with an organic solvent solution containing a polyfunctional acid halide to form a skeleton of the crosslinked polyamide separation functional layer through interfacial polycondensation.
The concentration of the polyfunctional acid halide in the organic solvent solution is preferably within the range of 0.01 to 10% by weight, more preferably within the range of 0.02 to 2.0% by weight. Within this range, the progress of the reaction will not be slowed down and side reactions will be less likely to occur. Furthermore, it is more preferable to include an acylation catalyst such as N,N-dimethylformamide in this organic solvent solution, since interfacial polycondensation is promoted.

Preferably, the organic solvent is immiscible with water, dissolves the polyfunctional acid halide, and does not destroy the microporous support membrane. Further, this organic solvent may be any solvent as long as it is inert to polyfunctional amines and polyfunctional acid halides. Preferred examples include liquid hydrocarbons and halogenated hydrocarbons such as trichlorotrifluoroethane, but they are substances that do not deplete the ozone layer, are easy to obtain, are easy to handle, and are safe in handling. In consideration of properties, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, heptadecane, hexadecane, etc., cyclooctane, ethylcyclohexane, 1-octene, 1-decene, etc., singly or in mixtures thereof are preferably used.

The method of contacting the organic solvent solution of the polyfunctional acid halide with the microporous support membrane after contact with the polyfunctional amine aqueous solution can be carried out in the same manner as the method for coating the microporous support membrane with the polyfunctional amine aqueous solution described above. good.

As mentioned above, after contacting an organic solvent solution of a polyfunctional acid halide to perform interfacial polycondensation and forming a separation functional layer containing crosslinked polyamide on a microporous support membrane, excess solvent is drained off. It's good to do that. As a method for draining the liquid, for example, a method can be used in which the membrane is held vertically and the excess organic solvent is removed by gravity. In this case, the time for vertical gripping is preferably between 1 and 5 minutes, more preferably between 1 and 3 minutes. 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, which will likely cause defects and cause performance deterioration.

(2-3) Other treatments The composite semipermeable membrane obtained by the above method is heated within the range of 40 to 100°C, preferably 60 to 100°C.
By adding a step of hot water treatment at 100° C. for 1 to 10 minutes, more preferably 2 to 8 minutes, the solute blocking performance and water permeability of the composite semipermeable membrane can be further improved.

Further, the composite semipermeable membrane obtained in the present invention is brought into contact with the compound (I) that reacts with the primary amino group on the separation functional layer to produce a diazonium salt or a derivative thereof after hot water treatment, and then the compound By including the step of bringing into contact a water-soluble compound (II) that is reactive with (I), the salt removal rate can be further improved.

Examples of the compound (I) that reacts with the primary amino group to be contacted to produce a diazonium salt or a derivative thereof include aqueous solutions of nitrous acid and its salts, nitrosyl compounds, and the like. Since an aqueous solution of nitrous acid or a nitrosyl compound is likely to generate gas and decompose, it is preferable to sequentially generate nitrous acid, for example, by reacting nitrite with an acidic solution.

Generally, nitrite reacts with hydrogen ions to produce nitrous acid (HNO ₂ ), which is efficiently produced when the pH of the aqueous solution is 7 or less, preferably 5 or less, more preferably 4 or less. Among these, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferred for ease of handling.

The concentration of compound (I), such as sodium nitrite, which reacts with the primary amino group to form a diazonium salt or a derivative thereof, is preferably in the range of 0.01 to 1% by weight. Within this range, a sufficient amount of diazonium salt or its derivative can be produced, and the solution can be easily handled.

The temperature of the compound is preferably 15°C to 45°C. Within this range, the reaction does not take too long, and nitrous acid does not decompose too quickly, making it easy to handle.

The contact time with the compound may be as long as it takes for the diazonium salt and/or its derivative to be produced; at high concentrations, the treatment can be carried out in a short period of time, but at low concentrations, a long period of time is required. Therefore, for a solution having the above concentration, the heating time is preferably within 10 minutes, and more preferably within 3 minutes.

Further, the method of contacting is not particularly limited, and the composite semipermeable membrane may be applied (coated) with a solution of the compound or immersed in a solution of the compound. Any solvent may be used to dissolve the compound as long as it dissolves the compound and does not erode the composite semipermeable membrane. Further, the solution may contain a surfactant, an acidic compound, an alkaline compound, etc. as long as they do not interfere with the reaction between the primary amino group and the reagent.

Next, the composite semipermeable membrane produced from the diazonium salt or its derivative is brought into contact with the water-soluble compound (II) that reacts with the diazonium salt or its derivative. The water-soluble compounds (II) that react with diazonium salts or derivatives thereof include chloride ions, bromide ions, cyanide ions, iodide ions, fluoroboric acid, hypophosphorous acid, sodium bisulfite, and sulfite ions. , aromatic amines, phenols, hydrogen sulfide, thiocyanic acid, etc.

When reacted with sodium bisulfite and sulfite ions, a substitution reaction occurs instantly, and the amino group is replaced with a sulfo group. In addition, when brought into contact with aromatic amines and phenols, a diazo coupling reaction occurs, making it possible to introduce aromatics onto the membrane surface. These compounds may be used alone, or may be used in combination, or may be contacted with different compounds multiple times. Preferred compounds to be contacted are sodium bisulfite and sulfite ions.

The concentration and time of contact with the water-soluble compound (II) that reacts with the diazonium salt or its derivative can be adjusted as appropriate to obtain the desired effect.

The temperature at which the mixture is brought into contact with the water-soluble compound (II) that reacts with the diazonium salt or its derivative is preferably 10 to 90°C. Within this temperature range, the reaction progresses easily, and at the same time, the amount of permeated water does not decrease due to shrinkage of the polymer.

(3) Utilization of composite semipermeable membrane The composite semipermeable membrane of the present invention manufactured in this way is made of raw water channel material such as plastic net, permeated water channel material such as tricot, and pressure resistance as required. It is wound around a cylindrical water collecting pipe with a large number of holes, together with a film for heightening, and is suitably used as a spiral-type composite semipermeable membrane element. Furthermore, these elements can be connected in series or in parallel to form a composite semipermeable membrane module housed in a pressure vessel.

Further, the above-described composite semipermeable membrane, its elements, and modules can be combined with a pump that supplies raw water to them, a device that pre-treats the raw water, etc. to configure a fluid separation device. By using this separation device, raw water can be separated into permeated water such as drinking water and concentrated water that has not passed through the membrane, and water suitable for the purpose can be obtained.

The higher the operating pressure of the fluid separation device, the better the salt removal rate, but the energy required for operation also increases.Also, considering the durability of the composite semipermeable membrane, it is necessary to The operating pressure during permeation is preferably 0.15 MPa or more and 10 MPa or less. As the feed water temperature increases, the salt removal rate decreases, but as it decreases, the membrane permeation flux also decreases, so it is preferably 5° C. or higher and 45° C. or lower. In addition, when the pH of the feed water becomes high, scales such as magnesium may occur in the case of feed water with high salt concentration such as seawater, and there is also a concern that membrane deterioration due to high pH operation may occur. It is preferable to drive at

The raw water to be treated by the composite semipermeable membrane of the present invention includes, for example, a liquid mixture containing 50 mg/L to 100 g/L of salt (Total Dissolved Solids) such as seawater, brine, and waste water. Can be mentioned. Generally, salt refers to the total amount of dissolved solids, and is expressed as "mass divided by volume" or "weight ratio". According to the definition, it can be calculated from the weight of the residue obtained by evaporating a solution filtered through a 0.45 micron filter at a temperature of 39.5 to 40.5 degrees Celsius, but it is more easily calculated from the practical salinity (S). do.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples in any way.

Measurements in Examples and Comparative Examples were performed as follows.

(membrane permeation flux)
The amount of water permeated through the membrane of the feed water (sodium chloride solution) was expressed as the amount of water permeated per day (cubic meters) per square meter of membrane surface (m3/m2/d).

(Salt removal rate)
A 500 mg/L sodium chloride (NaCl) aqueous solution 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 0.5 MPa, and the salt concentration in the permeated water was measured. The salt removal rate by the membrane was determined from the following formula.
Salt removal rate (%) = 100 x {1-(salt concentration in permeate water/salt concentration in feed water)}
(Measurement of the intermediate value of the height and thickness of the convex part)
The composite semipermeable membrane sample was embedded in epoxy resin, stained with osmium tetroxide to facilitate cross-sectional observation, and cut with an ultramicrotome to create 10 ultrathin sections. A cross-sectional photograph was taken of the obtained ultrathin section using a transmission electron microscope. The acceleration voltage during observation was 100 kV, and the observation magnification was 20,000 times. Regarding the obtained cross-sectional photograph, the number of convex portions at a distance of 2.0 μm 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, the height and thickness of all the convex parts in the cross-sectional photograph are scaled, with the part having a height of one-fifth or more of the 10-point average surface roughness as a convex part. were measured, and the respective intermediate values were determined.

(Amount of hydrogen bonded to aromatic ring carbon and hydrogen amount B bonded to non-aromatic ring carbon)
The base material was physically peeled off from a 2 m ² composite semipermeable membrane sample, and the separation functional layer was extracted using dichloromethane or the like. 2 mL of a 7N aqueous sodium hydroxide solution was added to 50 mg of the obtained separation functional layer, and the mixture was placed in a pressure container and heated at 120° C. for 2 hours. The obtained solution was made strongly acidic using hydrochloric acid, and then filtered. The filtrate was dried and dissolved in deuterated chloroform, and ¹ H NMR measurement was performed under the following conditions. The peak integrated value of the chemical shift 6 to 9.5 ppm excluding the peak derived from the solvent was defined as the amount A of hydrogen bonded to the aromatic ring carbon, and the peak integrated value of 0.7 to 4 ppm was defined as the amount B of hydrogen bonded to the non-aromatic ring carbon.
Equipment used: JNM-ECZ400R (manufactured by JEOL Ltd.)
Measurement method: single ¹ H pulse
Observation core: ¹ H
Observation frequency: 399.8MHz
Pulse width: 90°, 6.8μs
Number of X points: 16384
Accumulation count: 16 times Measurement temperature: 22℃
Sample rotation speed: 15Hz
(Reference example 1)
A 15.7% by weight DMF solution of polysulfone was cast on a polyester nonwoven fabric (air permeability 0.5 to 1 cc/cm2/sec) to a thickness of 200 μm at room temperature (25°C), and immediately immersed in pure water for 5 minutes. A microporous support membrane (thickness: 210 to 215 μm) was prepared by allowing the mixture to stand for a minute. The obtained microporous support membrane was cut into 20 cm square pieces, fixed on a metal frame, and immersed for 2 minutes in a 1.8% by weight aqueous solution of m-PDA as a polyfunctional amine aqueous solution. The support membrane was slowly lifted vertically from the aqueous solution, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the support membrane. Thereafter, 25 ml of n-decane solution at 25°C containing 0.065% by weight of TMC was poured into the frame so that the surface of the support membrane was completely wetted, and left to stand for 1 minute after the first contact between the n-decane solution and the support membrane. did. Next, the membrane was held vertically for 1 minute to remove excess solution from the membrane, drained, and then washed with 80° C. hot water for 2 minutes. The membrane after washing was further immersed in a 0.3 wt% sodium nitrite aqueous solution at 35°C and pH 3 for 1 minute, and then immersed in a 0.1 wt% sodium sulfite aqueous solution for 2 minutes to obtain a composite semipermeable membrane. .

(Comparative Examples 1 to 8, Examples 1 to 6)
A composite semipermeable membrane was obtained in the same manner as in Reference Example 1 except that the polyfunctional amine aqueous solution was changed.

Table 1 shows the median height of the convex part of the separation functional layer, the median thickness of the convex part, B/(A+B), membrane permeation flux, and salt removal rate as the composite semipermeable membrane performance of each obtained membrane. .

For membranes with B/(A+B) greater than 0.15, as in Comparative Examples 1 to 6, the height of the convex portion was significantly smaller than that of Reference Example 1, and the membrane permeation flux was also low. In addition, as in Comparative Example 7, in the case of a film with a thickness of less than 0.015, there was no significant change in the convex structure compared to the Reference Example, and the film performance was also the same. On the other hand, in Comparative Example 8, although B/(A+B) showed a value of 0.015 or more and 0.15 or less, the thickness of the convex portion was too small, resulting in a film with a significantly reduced salt removal rate.

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

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 contains a polyamide formed by interfacial polycondensation of an aliphatic amine and an aromatic amine with a polyfunctional acid halide,
The aliphatic amine is a piperazine derivative having a substituent at one or more of the 2, 3, 5, and 6 positions,
A composite semipermeable membrane in which an amount A of hydrogen bonded to aromatic ring carbon and an amount B of hydrogen bonded to non-aromatic ring carbon constituting the polyamide satisfy the following formula.
0.015≦B/(A+B)≦0.15 The separation functional layer has a pleated structure, and the median height of the convex portions in the pleated structure is 80 nm or more,
The composite semipermeable membrane according to claim 1 , wherein the median thickness of the convex portions in the pleated structure is 8 nm or more and 15 nm or less. A method for producing 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 method comprising:
comprising a step of forming a separation functional layer on the porous support layer,
The process includes:
forming a polyamide layer by interfacial polycondensation reaction by contacting a polyfunctional amine aqueous solution and a polyfunctional acid halide solution on the porous support layer;
The polyfunctional amine contained in the polyfunctional amine aqueous solution is an aliphatic amine and an aromatic amine,
The aliphatic amine is a piperazine derivative having a substituent at one or more of the 2, 3, 5, and 6 positions,
The amounts of the aliphatic amine and the aromatic amine contained in the polyfunctional amine aqueous solution are
0.01≦aliphatic amine [mol]/(aromatic amine + aliphatic amine) [mol] <0.1
The method for manufacturing a composite semipermeable membrane according to claim 1 or 2, which satisfies the following. The method for producing a composite semipermeable membrane according to claim 3, wherein the aromatic amine is m-phenylenediamine.