JP2021069988A - Composite semipermeable membrane, and filtration method using composite semipermeable membrane - Google Patents

Abstract

To provide a composite semipermeable membrane having a high silica removal rate, and having silica removal rate stability under a high temperature/existence of a heavy metal.SOLUTION: A composite semipermeable membrane has a microporous support layer, and a separation function layer provided on the microporous support layer. In the composite semipermeable membrane, the separation function layer contains crosslinked total aromatic polyamide as a main component, and an average thickness of the separation function layer determined from a cross-sectional image of a transmission electron microscope is 10 nm or more and 20 nm or less, and a nitrogen atom area density of the separation function layer determined from Rutherford backscatter is 8.0×1016/cm2 or more and 1.2×1017/cm2 or less.SELECTED DRAWING: Figure 1

Description

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

The membrane separation method is expanding as a method for removing a substance (for example, salts) dissolved in the solvent from a solvent (for example, water). The membrane separation method is attracting attention as an energy-saving and resource-saving method.

Membranes used in the membrane separation method include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes and the like. These films are used, for example, for the production of drinking water from seawater, brackish water, water containing harmful substances, the production of industrial ultrapure water, wastewater treatment, recovery of valuable resources, and the like (Patent Document 1). 2, 2).

Most of the reverse osmosis membranes and nanofiltration membranes currently on the market are composite semipermeable membranes. The composite semipermeable membrane has an active layer in which a gel layer and a polymer are crosslinked on a porous support layer, and an activity formed by polycondensing a monomer on the porous support layer and the porous support layer. There are two types, one with a layer and one with. Among the latter composite semipermeable membranes, the composite semipermeable membrane having a separation functional layer containing a crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide is permeable and selectively separable. Widely used as a high separation membrane.

The supply water filtered by the reverse osmosis membrane includes brackish water, seawater, etc., which may contain a water-soluble silicon derivative. Water-soluble silicon derivatives may be produced in the process of industry or may be derived from natural organisms such as diatoms.

Japanese Unexamined Patent Publication No. 55-14706 Japanese Unexamined Patent Publication No. 5-76740

For reverse osmosis membranes, improvement in removal performance of silicon derivatives (hereinafter referred to as silica) is required. When the raw water has a high temperature or contains heavy metals, the silica removability may decrease due to continuous operation, and a membrane capable of stable operation is required.

In order to achieve the above object, the composite semipermeable membrane of the present invention is a composite semipermeable membrane having a microporous support layer and a separation function layer provided on the microporous support layer.
The separation functional layer contains crosslinked total aromatic polyamide as a main component, and the average thickness of the separation functional layer obtained from a cross-sectional image of a transmission electron microscope is 10 nm or more and 20 nm or less.
The nitrogen atom plane density of the separation functional layer obtained from Rutherford backscatter is 8.4 × 10 ¹⁶ / cm ² or more and 1.2 × 10 ¹⁷ / cm ² or less.

According to the present invention, a film having a high silica removal rate and a silica removal rate stability in the presence of high temperature and heavy metals can be obtained.

It is a drawing explaining the photograph of the fold structure by TEM tomography.

The composite semipermeable membrane according to the present invention includes a support film including a base material and a porous support layer formed on the base material, and a separation functional layer formed on the porous support layer. The separation functional layer has substantially separation performance, and the support membrane does not substantially have separation performance of ions and the like, and can give strength to the separation functional layer.

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

The base material 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 base material is impregnated with the polymer solution serving as the porous support layer, so that the adhesiveness to the base material is improved and the physical stability of the support membrane is improved. Can be enhanced.
The thickness of the base material is preferably in the range of 10 to 200 μm, more preferably in the range of 30 to 120 μm. In this document, unless otherwise specified, the thickness means an average value. Here, the average value represents an arithmetic mean value. That is, the thickness of the base material and the porous support layer can be 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 (plane direction of the film) in the cross-sectional observation.

(1-2) Porous Support Layer In the present invention, the porous support layer is intended to give strength to a separation functional layer that does not substantially have separation performance such as ions and has substantially separation performance. .. The size and distribution of the pores of the porous support layer are not particularly limited, but for example, they have uniform and fine pores or gradually large fine pores from the surface on which the separation function layer is formed to the other surface. A porous support layer having a fine pore size of 0.1 nm or more and 100 nm or less on the surface on the side where the separation function layer is formed is preferable, but the material used and its shape are not particularly limited.

The material of the porous support layer may be, for example, a homopolymer or copolymer such as polysulfone, polyether sulfone, polyamide, polyester, cellulose-based polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, or alone. Can be blended and used. Here, as the cellulosic polymer, cellulose acetate, cellulose nitrate and the like can be used, and as the vinyl polymer, polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and 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 preferred. More preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfide can be mentioned, and among these materials, polysulfone has high chemical, mechanical, and thermal stability and is easy to mold. Can be used in general.
Polysulfone preferably has a mass average molecular weight (Mw) of 10,000 or more and 200,000 or less when measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard substance, more preferably. It is 15,000 or more and 100,000 or less. When Mw is 10,000 or more, preferable mechanical strength and heat resistance can be obtained as the porous support layer. Further, when Mw is 200,000 or less, the viscosity of the solution is in an appropriate range, and good moldability can be realized.

The thickness of the substrate 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. In this document, unless otherwise specified, the thickness means an average value. Here, the average value represents an arithmetic mean value. That is, the thickness of the base material and the porous support layer 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 (plane direction of the film) in the cross-sectional observation.

Also,
(1-3) Separation Function Layer In the present invention, the separation function layer contains a crosslinked total aromatic polyamide. In particular, the separation functional layer preferably contains crosslinked total aromatic polyamide as a main component. The principal component refers to a component that accounts for 50% or more of the components of the separation functional layer. The separation functional layer can exhibit high removal performance by containing 50% or more of the crosslinked total aromatic polyamide. Further, it is preferable that the separation functional layer is formed substantially only of the crosslinked total aromatic polyamide. That is, it is preferable that the crosslinked total aromatic polyamide occupies 90% by weight or more of the separation functional layer.

The crosslinked total aromatic polyamide can be formed by intercondensation 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 separation functional layer in the present invention may be hereinafter referred to as a polyamide separation functional layer.

The 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 primary. It means an aromatic amine which is an amino group. For example, examples of polyfunctional aromatic amines include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylene diamine, m-xylylene diamine, p-xylylene diamine, o-diaminopyridine, and m-. A polyfunctional aromatic amine in which two amino groups such as diaminopyridine and p-diaminopyridine are bonded to an aromatic ring at any of the ortho-position, meta-position, and para-position, 1,3,5-triaminobenzene. , 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine, 4-aminobenzylamine and other polyfunctional aromatic amines. In particular, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used in consideration of selective separability, permeability, and heat resistance of the membrane. Above all, it is more preferable to use m-phenylenediamine (hereinafter, also referred to as m-PDA) from the viewpoint of easy availability and ease of handling. 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. For example, trifunctional acid halides include trimesic acid chloride and the like, and bifunctional acid halides include biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, naphthalenedicarboxylic acid chloride and the like. Can be mentioned. Considering the reactivity with the polyfunctional aromatic amine, the polyfunctional aromatic acid halide is preferably a polyfunctional aromatic acid chloride, and considering the selective separability and heat resistance of the film, one molecule. It is preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups therein.

The removal rate of the target substance in the separation membrane is selectivity, and the higher the water permeability and the lower the solute permeability, the higher the removal rate. As a result of diligent studies, the inventors preferably have a small thickness of the thin film contained in the separation functional layer and a high density of the thin film in order to achieve a high silica removal rate. The average thickness is 10 nm or more and 20 nm or less, and the nitrogen atom plane density measured by Rutherford backscattering on the separation functional layer is 8.0 × 10 ¹⁶ pcs / cm ² or more and 1.2 × 10 ¹⁷ pcs / cm ² or less. I found that it was preferable.

When the thickness of the thin film is 10 nm or more or the nitrogen atomic surface density is 8.0 × 10 ¹⁶ pieces / cm ² or more, excellent silicon removal performance can be achieved, and the thickness is 20 nm or less or the nitrogen atomic surface density. High water permeability can be obtained when the number is 1.2 × 10 ¹⁷ pieces / cm ^{2 or less.}

The separating functional layer may have a nanometer-sized pleated structure. The fold structure is suitable for efficient filtration because it can increase the specific surface area of the separation function layer. On the other hand, when the separating functional layer has a fold structure, it has been clarified that there may be variations depending on the location of the fold structure, particularly variations in the structure depending on the distance from the support membrane. This is because the separation functional layer is formed by the interfacial polymerization of the aqueous layer and the oil layer. The structure differs between the support film side near the water layer and the tip of the fold near the oil layer.

This structural variation can be measured by several methods, including transmission electron microscopy (TEM) tomography. As shown in FIG. 1, a cross-sectional image (cross-section parallel to the film surface) is obtained by TEM tomography at distances of 25 nm, 50 nm, and 75 nm from the support film. The cross-sectional image is set to 256 gradations from the darkest place to the brightest place, and the average brightness of each of the 20 polyamide cross-sections is calculated for each cross-section, and the values corresponding to the densities of the three locations are obtained to obtain the fold structure. Vertical uniformity can be evaluated.

In order to achieve both the silica removal rate and its durability, the difference obtained above is preferably 20 gradations or less, and more preferably 15 gradations or less.

The polyamide separation functional layer contains an amide group derived from the polymerization of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide, and an amino group and a carboxy group derived from an unreacted functional group. Regarding the number of each functional group per area, the silica removal rate and its durability ^{are preferably such that the areal density of amino groups is 3.0 × 10 16} / cm ² or less, and the areal density of carboxy groups is 2.0 ×. 10 ¹⁶ pieces / cm ² or more is preferable. This is because the amino group becomes the starting point of oxidative deterioration and the carboxy group imparts hydrophilicity to the film. The number of each functional group ^{can be calculated, for example, from the 13} C solid-state NMR measurement of the separation functional layer and the result of Rutherford backscattering.

¹³ C solid-state NMR measurement can be performed as follows. The base material is peeled off from the composite semipermeable membrane 5 m ² to obtain a polyamide separation functional layer and a porous support layer, and then the porous support layer is dissolved and removed to obtain a polyamide separation functional layer. The obtained polyamide separation functional layer is ^{measured by DD / MAS-13} C solid-state NMR method, and each ratio is calculated by comparing the integrated values of the carbon peaks of each functional group or the carbon peaks to which each functional group is bonded. ..

Furthermore, the areal density per area of the element can be calculated from Rutherford backscatter, and the number density of each functional group can be obtained.

2. Method for Producing Composite Semipermeable Membrane Next, the method for producing the composite semipermeable membrane will be described. The composite semipermeable membrane includes a step of forming a porous support layer on the base material and a step of forming a separation functional layer on the porous support layer.

(2-1) Formation of Porous Support Layer Examples of the base material and the porous support layer include "Millipore Filter VSWP" (trade name) manufactured by Millipore and "Ultra Filter UK10" (trade name) manufactured by Toyo Filter Paper Co., Ltd. It is also possible to select an appropriate film from various commercially available films.

In addition, "Office of Saline Water Research and Development Progress Report" No. It can be produced according to the method described in 359 (1968). In addition, a known method is preferably used as a method for forming the porous support layer.

(2-2) Method for Producing Separation Function Layer Next, a step of forming the separation function layer constituting the composite semipermeable membrane will be described. The process of forming the separating functional layer is
(A) A step of bringing an aqueous solution containing a polyfunctional aromatic amine into contact with the porous support layer, and
(B) A step of contacting a porous support layer with an aqueous solution containing a polyfunctional aromatic amine with an organic solvent solution containing a polyfunctional aromatic acid halide.
(C) Step of heating the porous support layer in contact with an organic solvent solution containing a polyfunctional aromatic halide.
(d) It has a step of removing a low-density part from the membrane after the reaction to control the density and thickness.

In the step (a), the concentration of the polyfunctional aromatic amine in the aqueous solution of the polyfunctional aromatic amine is preferably in the range of 0.1% by weight or more and 20% by weight or less, and more preferably 0.5% by weight or more and 15% by weight. It is within the range of weight% or less. When the concentration of the polyfunctional aromatic amine is in this range, sufficient solute removal performance and water permeability can be obtained. The polyfunctional aromatic amine aqueous solution contains a surfactant, an organic solvent, an alkaline compound, an antioxidant, etc. as long as it does not interfere with the reaction between the polyfunctional aromatic amine and the polyfunctional aromatic acid halide. May be. The surfactant has the effect of improving the wettability of the surface of the support film and reducing the interfacial tension between the aqueous polyfunctional aromatic amine solution and the non-polar solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and by adding it, the interfacial polycondensation reaction may be efficiently performed.

The contact of the polyfunctional aromatic amine aqueous solution is preferably performed uniformly and continuously on the porous support layer. Specifically, for example, a method of coating the porous support layer with the polyfunctional aromatic amine aqueous solution and a method of immersing the porous support layer in the polyfunctional aromatic amine aqueous solution can be mentioned. 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.

After the polyfunctional amine aqueous solution is brought into contact with the porous support layer, the liquid 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 droplet from becoming a film defect and deteriorating the removal performance after the formation of the porous support layer. As a method of draining the liquid, for example, as described in Japanese Patent Application Laid-Open No. 2-784428, a method of vertically grasping the support membrane after contact with the polyfunctional amine aqueous solution and allowing the excess aqueous solution to flow down naturally. A method of forcibly draining the liquid by blowing an air stream such as nitrogen from the air nozzle can be used. Further, after draining the liquid, the film surface can be dried to remove a part of the water content of the aqueous solution.

In step (b), the concentration of the polyfunctional acid halide in the organic solvent solution is preferably in the range of 0.01% by weight or more and 10% by weight or less, and 0.02% by weight or more and 2.0% by weight or less. It is more preferable that it is within the range of. This is because a sufficient reaction rate can be obtained when the content is 0.01% by weight or more, and the occurrence of side reactions can be suppressed when the content is 10% by weight or less. Further, when the acylation catalyst is contained in this organic solvent solution, interfacial polycondensation is promoted, which is more preferable.

The organic solvent is preferably immiscible with water, dissolves the polyfunctional acid halide and does not destroy the support film, and is inactive against the polyfunctional amine compound and the polyfunctional acid halide. All you need is. Preferred examples include hydrocarbon compounds such as n-hexane, n-octane, n-decane and isooctane.

The method of contacting the porous support layer in which the organic solvent solution of the polyfunctional aromatic acid halide is brought into contact with the aqueous solution of the polyfunctional aromatic amine compound is the method of coating the porous support layer of the aqueous solution of the polyfunctional aromatic amine. You can do the same.

In step (c), the porous support layer contacted with the organic solvent solution of the polyfunctional aromatic acid halide is heated. The temperature for heat treatment is 50 ° C. or higher and 180 ° C. or lower, preferably 60 ° C. or higher and 160 ° C. or lower. In order to obtain a high-density polyamide functional layer, 80 ° C. or higher is more preferable. The optimum heating time varies depending on the temperature of the membrane surface which is the reaction field, but is preferably 10 seconds or longer, more preferably 20 seconds or longer.

In step (d), the low-density portion is removed from the polyamide separation functional layer, and the thickness is adjusted at the same time. For example, it can be carried out by bringing radicals into contact with the film surface. Various radicals can be used, and examples thereof include hydroxyl radical, hydroperoxy radical, peroxy radical, alkoxy radical, thiyl radical, and sulfite radical. Of these, sulfurous acid radicals are preferable in terms of ease of controlling the intensity and concentration of radicals. Further, chlorine radicals and persulfate radicals that react with the benzene ring of the crosslinked aromatic polyamide and cause chemical deterioration are not preferable. Reaction conditions such as concentration, temperature and pH need to be appropriately controlled by the activity of the radicals used. High concentration and high activity conditions with high strength such that the amide bond is oxidatively deteriorated and the polyamide is decomposed are not preferable.

3. 3. Utilization of Composite Semipermeable Membrane The composite semipermeable membrane of the present invention has a large number of holes together with a supply water flow path material such as a plastic net, a permeation water flow path material such as a tricot, and a film for increasing pressure resistance as required. Is wound around a tubular water collecting pipe, and is suitably used as a spiral type composite semipermeable membrane element. Further, the elements can be connected in series or in parallel to form a composite semipermeable membrane module housed in a pressure vessel.

Further, the composite semipermeable membrane, its elements, and modules can be combined with a pump for supplying supply water to them, a device for pretreating the supplied water, and the like to form a fluid separation device. By using this separation device, the supplied water can be separated into permeated water such as drinking water and concentrated water that has not permeated the membrane, and water suitable for the purpose can be obtained.

As the supply 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) such as seawater, brackish water, and wastewater is used. Can be mentioned. Generally, TDS refers to the total amount of dissolved solids and is expressed as "mass ÷ volume" or "weight ratio". According to the definition, a solution filtered through a 0.45 micron filter is evaporated at a temperature of 39.5 ° C. or higher and 40.5 ° C. or lower and can be calculated from the weight of the residue, but more simply, the practical salt content (S). Convert from. The composite semipermeable membrane is preferably used because it can exhibit high removal performance when an aqueous solution containing a water-soluble silicon derivative of 1 mg / L or more is used as feed water. In addition, the supplied water containing a large amount of iron (III) ions has a risk of deterioration to the membrane, but the composite semipermeable membrane has high removal performance stability, so that the iron (III) ions of 0.01 mg / L or more are present. Water having the above can be used as supply water.

The higher the operating pressure of the fluid separator, the better the solute removal rate, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, water to be treated is applied to the composite semipermeable membrane. The operating pressure for permeation is preferably 0.5 MPa or more and 10 MPa or less. The temperature of the supply water is preferably 5 ° C. or higher because the membrane permeation flux decreases as the temperature decreases. Although the solute removal rate decreases as the temperature rises, the composite semipermeable membrane has high removal performance stability, so that water having a temperature of 28 ° C. or higher can be preferably used as the feed water. The supply water temperature is preferably 55 ° C. or lower. In addition, when the pH of the supplied water becomes high, scales such as magnesium may be generated in the case of supplied water having a high solute concentration such as seawater, and there is a concern that the membrane may deteriorate due to high pH operation. It is preferable to operate in.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Analysis of functional groups and compositions in Examples and Comparative Examples, and the residual rate of water were measured as follows. Hereinafter, unless otherwise specified, the operation was performed at 25 ° C.

(Quantification of nitrogen amount)
The composite semipermeable membrane 100 cm ² was used as it was. After washing with pure water for 24 hours, the Rutherford backscattering method (RBS) was measured using Pelletron 3SDH manufactured by National Electrostatics Corporations. The measurement conditions are shown below.

Incident ions: ⁴ He ²⁺
Incident energy: 2300 keV
Angle of incidence: 0deg
Scattering angle: 160deg
Sample current: 4nA
Beam diameter: 2mmφ
Irradiation: 0.8 μC x 126 points = 100.8 μC
(Electron Microscope Tomography)
The separation function layer of the composite semipermeable membrane was embedded in an epoxy chemical solution to defoam, and ultrathin sections were obtained with a microtome, and then transmission electron microscopic tomography was measured using JEM-F200 manufactured by JEOL Ltd. .. The acceleration voltage was 200 kV.

(Quantification of carboxy group, amino group, amide group)
The base material was physically peeled off from the composite semipermeable membrane 5 m ² , and the porous support layer and the separating functional layer were recovered. After drying by allowing to stand for 24 hours, it was added little by little to a beaker containing dichloromethane and stirred to dissolve the polymer constituting the porous support layer. The insoluble matter in the beaker was collected with filter paper. This insoluble matter was placed in a beaker containing dichloromethane and stirred to recover the insoluble matter in the beaker. This process was repeated until the elution of the polymer forming the porous support layer in the dichloromethane solution could not be detected. The recovered separation functional layer was dried in a vacuum dryer to remove residual dichloromethane. The obtained separation functional layer was made into a powder sample by freeze-grinding, sealed in a sample tube used for ^{solid-state NMR measurement, and 13} C solid-state NMR measurement was performed by CP / MAS method and DD / MAS method. ^{For 13} C solid-state NMR measurement, for example, CMX-300 manufactured by Chemagnetics can be used. The measurement conditions are shown below.

Reference substance: Polydimethylsiloxane (internal standard: 1.56 ppm)
Sample rotation speed: 10.5kHz
Pulse repetition time: 100s
From the obtained spectrum, peak division was performed for each peak derived from the carbon atom to which each functional group was bonded, and the functional group amount ratio was quantified from the area of the divided peak. The density of each functional group was calculated together with the amount of nitrogen obtained above.

Various properties of the composite semipermeable membrane, the composite semipermeable membrane, 50 ppm corresponds saline adjusted to pH6.5 with (NaCl concentration 500 ppm) sodium silicate _{(Na 2 SiO 3 · 9H 2} O) as a SiO ₂ It was determined by measuring the quality of the permeated water and the supplied water after the membrane filtration treatment was performed for 3 hours by supplying the mixture at an operating pressure of 0.75 MPa.

(Radical concentration)
Radical concentrations were measured using electron spin resonance (ESR). The apparatus used was ESP350E (manufactured by BRUKER), and the microwave frequency counter used was HP5351B (manufactured by HEWLETT PACKARD). An example of measurement conditions is shown below.
Measurement temperature: 25 ° C
Magnetic field sweep range: 3385-3595G
Modulation: 100kHz, 1G
Microwave: 4mW, 9.81GHz
Sweep time 41.94 seconds, number of measurements: 1 time constant: 81.92 ms
Number of data points: 1024 points Cavity: TM110, Cylindrical spin trap reagent: 5-dimethyl-1-pyrroline-N-oxide (DMPO), concentration was quantified by analyzing spin adduct with radicals.

(Membrane permeation flux)
The amount of membrane permeation of the supplied water (seawater) was expressed as the ^{membrane permeation flux (m 3} / m ² / day) by the amount of water permeation per day (cubic meter) per square meter of the membrane surface.

(Boron removal rate)
The boron concentrations in the supplied water and the permeated water were analyzed by an ICP emission spectrometer (5110 ICP-OES manufactured by Agilent Technologies) and calculated from the following formula.

Silica removal rate (%) = 100 × {1- (silica concentration in permeated water / silica concentration in feed water)}
(Durability accelerated test)
A 50 ° C aqueous solution prepared by adding 10 ppm of iron (III) chloride to a saline solution (NaCl concentration of 500 ppm) adjusted to pH 6.5 was supplied to the composite semipermeable membrane at an operating pressure of 0.75 MPa to perform membrane filtration treatment. After a period of time, the mixture was thoroughly washed with water, and the silica removal rate of the composite semipermeable membrane was evaluated again by the above method.

(Preparation of support film)
Supported by casting a 16.0 wt% DMF solution of polysulfone (PSf) on a polyester non-woven fabric (ventilation volume 2.0 cc / cm2 / sec) to a thickness of 200 μm, immediately immersing it in pure water and leaving it for 5 minutes. A membrane was prepared.

(Example 1)
A 3.0 wt% aqueous solution of m-phenylenediamine was prepared. The support membrane obtained by the above operation is immersed in the above aqueous solution for 2 minutes, the support membrane is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support membrane surface, and then trimesic acid is used. A decan solution at 45 ° C. containing 0.2% by weight of chloride (TMC) is applied so that the surface is completely wet, allowed to stand for 10 seconds, then heated in an oven at 120 ° C. for 10 minutes, and then heated at 90 ° C. It was washed with water for 2 minutes to obtain a composite semipermeable membrane. ^{Furthermore, an aqueous solution containing 1.0 × 10 -3} mol / L sulfite radicals at 25 ° C. and pH 3 was prepared by bubbling oxygen in an aqueous sodium hydrogen sulfite solution, and the composite semipermeable membrane was immersed in this solution for 1 hour. After further immersing in a 10 wt% isopropyl alcohol aqueous solution for 1 hour, it was immersed in pure water for 1 hour. By the above operation, the composite semipermeable membrane in Example 1 was obtained.

(Example 2)
A 3.0 wt% aqueous solution of m-phenylenediamine was prepared. The support film obtained by the above operation is immersed in the above aqueous solution for 2 minutes, the support film is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support film surface, and then TMC0. A 45 ° C. decan solution containing 2% by weight is applied so that the surface is completely wet, allowed to stand for 10 seconds, then heated in an oven at 120 ° C. for 2 minutes, washed with hot water at 90 ° C. for 2 minutes, and combined. A semipermeable membrane was obtained.

Then, by bubbling oxygen into an aqueous solution of sodium hydrogen sulfite, an aqueous solution ^{containing 1.0 × 10 -3} mol / L sulfite radicals at 25 ° C and pH 3 is prepared, and the composite semipermeable membrane is immersed in this solution for 1 hour. The composite semipermeable membrane in Example 2 was obtained.
(Example 3)
A composite semipermeable membrane in Example 3 was obtained in the same manner as in Example 1 except that the sulfite radical concentration was 2.5 × 10 ^{-5 mol / L.}
(Example 4)
A composite semipermeable membrane in Example 4 was obtained in the same manner as in Example 2 except that the sulfite radical concentration was 2.5 × 10 ^{-5 mol / L.}

(Comparative example 1)
A 3.0 wt% aqueous solution of m-phenylenediamine was prepared. The support film obtained by the above operation is immersed in the above aqueous solution for 2 minutes, the support film is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support film surface, and then TMC0. A 45 ° C. decan solution containing 2% by weight is applied so that the surface is completely wet, allowed to stand for 10 seconds, heated in an oven at 120 ° C. for 10 minutes, and then washed with hot water at 90 ° C. for 2 minutes. A composite semipermeable membrane was obtained. This membrane was immersed in a 10 wt% isopropyl alcohol aqueous solution for 1 hour and then immersed in pure water for 1 hour to obtain a composite semipermeable membrane in Comparative Example 1.

(Comparative example 2)
A 3.0 wt% aqueous solution of m-phenylenediamine was prepared. The support film obtained by the above operation is immersed in the above aqueous solution for 1 minute, the support film is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support film surface, and then TMC0. A decane solution at 25 ° C. containing 06% by weight and trimellitic anhydride chloride added so that the molar ratio to TMC was 0.63 was applied so that the surface was completely wet, and then allowed to stand for 10 seconds. , 30 ° C., dried for 1 minute with warm air. Then, it was washed with hot water of 90 degreeC for 2 minutes, and the composite semipermeable membrane in Comparative Example 2 was obtained.

(Comparative example 3)
A 3.8 wt% aqueous solution of m-phenylenediamine was prepared. The support film obtained by the above operation is immersed in the above aqueous solution for 2 minutes, the support film is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support film surface, and then TMC0. A 40 ° C. decan solution containing 165% by weight was applied so that the surface was completely wet, allowed to stand for 10 seconds, heated in an oven at 120 ° C. for 15 seconds, and then washed with hot water at 90 ° C. for 2 minutes. Then, the composite semipermeable membrane in Comparative Example 3 was obtained.

(Comparative example 4)
A 2.0 wt% aqueous solution of m-phenylenediamine was prepared. The support film obtained by the above operation is immersed in the above aqueous solution for 2 minutes, the support film is slowly pulled up in the vertical direction, nitrogen is blown from an air nozzle to remove excess aqueous solution from the support film surface, and then TMC0. A 25 ° C. trichlorotrifluoroethane solution containing 1% by weight was applied so that the surface was completely wet, allowed to stand for 10 seconds, and then dried with air at 25 ° C. to obtain the composite semipermeable membrane in Comparative Example 4. Obtained.

Table 1 shows the structure and performance of the above film. As shown in Examples, it can be seen that the composite semipermeable membrane of the present invention has a high silica removal rate and a silica removal rate stability in the presence of high temperature and heavy metals.

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

Claims (8)

A composite semipermeable membrane having a microporous support layer and a separation function layer provided on the microporous support layer.
The separating functional layer contains thin film folds containing a crosslinked total aromatic polyamide.
The average thickness of the thin film determined from the cross-sectional image of the transmission electron microscope is 10 nm or more and 20 nm or less.
A composite semipermeable membrane having a nitrogen atomic surface density of 8.0 × 10 ¹⁶ / cm ² or more and 1.2 × 10 ¹⁷ / cm ^{2 or less obtained from Rutherford backscattering.} Average brightness of 20 folds in each section of 256 gradations obtained by transmission electron microscopic tomography at distances 25 nm, 50 nm and 75 nm from the porous support layer B25, B50, B75 The composite semipermeable membrane according to claim 1, wherein the maximum value of the difference between the two is 20 gradations or less. The composite semipermeable membrane according to claim 1 or 2, wherein the surface density of amino groups contained in the separation functional layer, which is calculated from Rutherford backscatter and ^{13 C solid-state NMR, is 2.0 × 10 16} pieces / cm ^{2 or less.} film. The composite semipermeable membrane according to any one of claims 1 to 3, wherein the separation functional layer contains 90% or more of a polyamide which is a polymer of trimesic acid chloride and m-phenylenediamine. Using the spiral element having the composite semipermeable membrane according to any one of claims 1 to 4, from an aqueous solution containing a water-soluble silicon derivative of 1 mg / L or more, a permeate and a silicon derivative concentration higher than that of the permeate. A method for filtering an aqueous solution, which comprises the step of producing a highly concentrated solution. The method for filtering an aqueous solution according to claim 5, wherein the temperature of the aqueous solution is 28 ° C. or higher. The method for filtering an aqueous solution according to claim 5 or 6, wherein the aqueous solution contains iron (III) ions of 0.01 mg / L or more. The method for filtering an aqueous solution according to any one of claims 5 to 7, wherein the operating pressure is 5.0 MPa or more.

Images