CN108430612B

CN108430612B - Composite semipermeable membrane

Info

Publication number: CN108430612B
Application number: CN201680075419.0A
Authority: CN
Inventors: 佐藤一树; 佐佐木崇夫
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2015-12-25
Filing date: 2016-12-21
Publication date: 2021-04-20
Anticipated expiration: 2036-12-21
Also published as: CN108430612A; JPWO2017110898A1; WO2017110898A1

Abstract

本发明的复合半透膜具备支承膜和分离功能层，其中，分离功能层含有芳香族聚酰胺，芳香族聚酰胺具有硝基作为与芳香族环相键合的官能团，将芳香族聚酰胺中的来自硝基的氮原子数的合计设为A、将芳香族聚酰胺中的总氮原子数设为B，若利用X射线光电子能谱法(XPS)对A和B进行分析，则当将从分离功能层的一侧的面照射X射线时的A/B设为C、将从所述分离功能层的另一侧的面照射X射线时的A/B设为D时，分离功能层满足C‑D≥0.010，并且，上述分离功能层的上述另一侧的面与上述支承膜相接触。The composite semipermeable membrane of the present invention includes a support membrane and a separation functional layer, wherein the separation functional layer contains an aromatic polyamide, and the aromatic polyamide has a nitro group as a functional group bonded to an aromatic ring. The sum of the number of nitrogen atoms derived from the nitro group is A, the total number of nitrogen atoms in the aromatic polyamide is B, and when A and B are analyzed by X-ray photoelectron spectroscopy (XPS), when the When A/B when X-rays are irradiated from one surface of the separation functional layer is set to C, and A/B when X-rays are irradiated from the other surface of the separation functional layer is set to D, the separation functional layer C-D≧0.010 is satisfied, and the other surface of the separation functional layer is in contact with the support film.

Description

Composite semipermeable membrane

Technical Field

The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture, and to a composite semipermeable membrane having high oxidation resistance, acid resistance and alkali resistance.

Background

There are various techniques for separating a mixture to remove substances (e.g., salts) dissolved in a solvent (e.g., water), and in recent years, a membrane separation method has been widely used as a process for saving energy and resources. As membranes used in the membrane separation method, there are microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, and the like, and these membranes are used in the case of obtaining drinking water from, for example, seawater, brackish water, water containing harmful substances, and the like, and are used in the production of industrial ultrapure water, wastewater treatment, recovery of valuable substances, and the like.

Most of the currently marketed reverse osmosis membranes and nanofiltration membranes are composite semipermeable membranes, and the composite semipermeable membranes comprise the following two types: a composite semipermeable membrane having a gel layer and an active layer obtained by crosslinking a polymer on a microporous support membrane; and a composite semipermeable membrane having an active layer obtained by condensing a monomer on a microporous support membrane. Among them, composite semipermeable membranes (patent documents 1 to 4) in which a separation functional layer containing crosslinked polyamide obtained by polycondensation reaction between polyfunctional amine and polyfunctional acid halide is coated on a microporous support membrane have been widely used as separation membranes having high permeability and high selective separation performance.

However, if the composite semipermeable membrane is continuously used, there is a problem that the separation performance of the membrane is lowered due to contact with an oxidizing substance such as free chlorine contained in the water to be treated. In addition, as the use time passes, dirt adheres to the membrane surface, and the membrane permeation flux of the membrane decreases. Therefore, after a certain period of operation, it is necessary to perform chemical cleaning with an acid, an alkali, or the like, but this has the problem of lowering the separation performance of the membrane.

Therefore, in order to continue stable operation for a long period of time, development of a composite semipermeable membrane having high oxidation resistance and little change in membrane performance before and after cleaning with a chemical such as acid or alkali (i.e., high acid resistance) has been desired.

As means for improving the oxidation resistance, patent documents 5 and 6 disclose a method of bringing persulfate into contact with a composite semipermeable membrane.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 55-147106

Patent document 2: japanese patent laid-open publication No. 62-121603

Patent document 3: japanese patent laid-open publication No. 63-218208

Patent document 4: japanese laid-open patent application No. 2001-79372

Patent document 5: japanese laid-open patent publication No. 2008-100214

Patent document 6: japanese patent laid-open No. 2010-234284

Disclosure of Invention

Problems to be solved by the invention

The films disclosed in patent documents 5 and 6 are excellent in oxidation resistance, but a film having durability to an alkaline chemical solution is also desired.

Accordingly, an object of the present invention is to provide a composite semipermeable membrane which has oxidation resistance, and which has less change in membrane performance even after chemical cleaning, and which is excellent in acid resistance and alkali resistance.

Means for solving the problems

The composite semipermeable membrane of the present invention for achieving the above object has the following configurations [1] to [6 ].

[1] A composite semipermeable membrane comprising a support film and a separation functional layer provided on the support film, wherein the separation functional layer contains an aromatic polyamide, the aromatic polyamide is a polymer of a polyfunctional aromatic amine and a polyfunctional aromatic carboxylic acid derivative, the aromatic polyamide has a nitro group as a functional group bonded to an aromatic ring, the number of nitrogen atoms derived from the nitro group in the aromatic polyamide is A, the total number of nitrogen atoms in the aromatic polyamide is B, and when A and B are analyzed by X-ray photoelectron spectroscopy (XPS), C-D of the separation functional layer is 0.010 or more when A/B when X-ray irradiation is performed from one surface of the separation functional layer and A/B when X-ray irradiation is performed from the other surface of the separation functional layer is D, the other surface of the separation functional layer is in contact with the support film.

[2] The composite semipermeable membrane according to [1], wherein when the analysis is performed by irradiating X-rays from the surface on the one side of the separation functional layer by the X-ray photoelectron spectroscopy (XPS), E is 1.00. ltoreq. E/B.ltoreq.1.20, where E represents the total number of oxygen atoms in the polyamide.

[3] The composite semipermeable membrane according to [1] or [2], wherein C-D is 0.20 or less.

[4] The composite semipermeable membrane according to any of the above [1] to [3], wherein C-D is 0.030 or more.

[5] The composite semipermeable membrane according to any of the above [1] to [4], which is used for treating a liquid mixture having TDS (total dissolved solids) of 500mg/L to 100 g/L.

[6] A composite semipermeable membrane element comprising the composite semipermeable membrane according to any one of the above [1] to [5 ].

Effects of the invention

According to the present invention, a composite semipermeable membrane (i.e., separation membrane) having high oxidation resistance, high acid resistance, and high alkali resistance can be obtained. The composite semipermeable membrane of the present invention can be particularly suitably used for desalination of seawater.

Detailed Description

I. Composite semipermeable membrane

(1) Support film

In the present embodiment, the support membrane includes a substrate and a porous support layer. However, the present invention is not limited to this configuration.

(1-1) base Material

Examples of the base material include polyester polymers, polyamide polymers, polyolefin polymers, and mixtures and copolymers thereof. Among them, a polyester polymer fabric having high mechanical stability and high thermal stability is particularly preferable.

As the form of the fabric, a long fiber nonwoven fabric, a short fiber nonwoven fabric, and a woven fabric can be preferably used. The long fiber nonwoven fabric is a nonwoven fabric having an average fiber length of 300mm or more and an average fiber diameter of 3 to 30 μm.

The air permeability of the substrate is preferably 0.5cc/cm²At least 5.0 cc/cm/sec²And less than second. When the air permeability of the substrate is within the above range, the polymer solution forming the porous support layer is easily impregnated into the substrate, and therefore, the adhesiveness between the substrate and the porous support layer is improved, and the physical stability of the obtained porous support film can be improved.

The thickness of the base material is preferably within a range of 10 to 200 μm, and more preferably within a range of 30 to 120 μm. In the present specification, unless otherwise specified, the thickness means an average value. The average here means an arithmetic average. Specifically, the thickness was determined by measuring the thickness at 20 points at 20 μm intervals in the direction perpendicular to the thickness direction (the film surface direction) in cross-sectional observation, and calculating the average value of the measured values.

(1-2) porous support layer

The porous support layer does not substantially have a separation performance against ions or the like, and is used to impart strength to the separation function layer having a separation performance substantially. The material used for the porous support layer and the shape thereof are not particularly limited, and the size and distribution of the pores of the porous support layer are not particularly limited, but the following porous support layers are preferred: for example, a porous support layer having uniform and fine pores; or a porous support layer having micropores which gradually increase from the surface on the side where the separation functional layer is formed to the surface on the other side, and the size of the micropores on the surface on the side where the separation functional layer is formed being 0.1nm or more and 100nm or less.

As the material of the porous support layer, a homopolymer or a copolymer such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymer, vinyl polymer (vinyl polymer), polyphenylene sulfide sulfone, polyphenylene ether, or the like can be used alone or in combination. Here, cellulose acetate, cellulose nitrate, and the like can be used as the cellulose-based polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, and the like can be used as the vinyl polymer. Among them, preferred are homopolymers or copolymers such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide sulfone and the like. More preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone or polyphenylene sulfone, and among these materials, polysulfone is usually used in view of its high chemical stability, mechanical stability and thermal stability and easy molding.

Specifically, when polysulfone containing a repeating unit represented by the following chemical formula is used, the pore diameter of the porous support layer can be easily controlled, and the dimensional stability is high, which is preferable.

[ chemical formula 1]

In the above formula, n represents the number of repeating units.

The polysulfone has a weight average molecular weight (Mw) of preferably 10000 or more and 200000 or less, more preferably 15000 or more and 100000 or less, as measured by Gel Permeation Chromatography (GPC) using N-methylpyrrolidone as a solvent and polystyrene as a standard substance. When Mw is 10000 or more, mechanical strength and heat resistance preferable for the porous support layer can be obtained. Further, when Mw is 200000 or less, the viscosity of the solution falls within an appropriate range, and good moldability can be achieved.

For example, a porous supporting layer having fine pores with a diameter of 10nm or less in most of the surface can be obtained by casting a solution of polysulfone in N, N-dimethylformamide (hereinafter referred to as DMF) onto a densely woven polyester cloth or nonwoven fabric as a base material at a constant thickness and then wet-solidifying the solution in water. The porous supporting layer may be formed on at least one of the 2 surfaces of the substrate, and may be arbitrarily selected depending on the desired film thickness and application of the composite semipermeable membrane.

The thickness of the substrate and porous supporting layer will have an effect on the strength of the composite semipermeable membrane and the packing density of the composite semipermeable membrane when it is formed into 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.

(2) Separating functional layer

The separation functional layer contains an aromatic polyamide. In the present specification, unless otherwise specified, "polyamide" means "aromatic polyamide". The content of the polyamide in the separation functional layer is preferably 80 wt% or more, and more preferably 90 wt% or more. The separation functional layer may be formed substantially only of polyamide.

The polyamide is a polymer of a polyfunctional aromatic amine and a polyfunctional aromatic carboxylic acid derivative, and can be formed by interfacial polycondensation between the polyfunctional aromatic amine and the polyfunctional aromatic carboxylic acid derivative. Here, it is preferable that at least one of the polyfunctional aromatic amine and the polyfunctional aromatic carboxylic acid derivative contains a compound having three or more functions.

The polyfunctional aromatic amine is an amine having at least 2 primary and/or secondary amino groups in one molecule. Examples of the polyfunctional aromatic amine include aromatic polyfunctional amines such as phenylenediamine, xylylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, and 3, 5-diaminobenzoic acid, in which 2 amino groups are bonded to a benzene ring in any of the ortho, meta, and para positions. Among them, in view of the selective separation property, permeability, and heat resistance of the film, polyfunctional aromatic amines having 2 to 4 primary and/or secondary amino groups in one molecule are preferable, and m-phenylenediamine, p-phenylenediamine, and 1,3, 5-triaminobenzene are preferably used as such polyfunctional aromatic amines. Among them, m-phenylenediamine (hereinafter referred to as m-PDA) is more preferably used from the viewpoint of easy availability and easy handling. These polyfunctional aromatic amines may be used alone or in combination of two or more.

The polyfunctional aromatic carboxylic acid derivative is an aromatic acid halide having at least 2 halogenated carbonyl groups in one molecule. Examples of the polyfunctional aromatic carboxylic acid derivative include aromatic bifunctional acid halides such as trimesoyl chloride in the case of trifunctional acid halide, biphenyldicarbonyl chloride, azobenzenedicarbonyl chloride, terephthaloyl chloride, isophthaloyl chloride and naphthalenedicarboxylic acid chloride in the case of bifunctional acid halide. The polyfunctional aromatic carboxylic acid derivative is preferably a polyfunctional acid chloride in view of reactivity with a polyfunctional amine, and is preferably a polyfunctional aromatic acid chloride having 2 to 4 chlorocarbonyl groups (carbonyl chloride groups) in one molecule in view of selective separation and heat resistance of the film. Among them, trimesoyl chloride is more preferably used from the viewpoint of easy availability and easy handling. These polyfunctional aromatic carboxylic acid derivatives may be used alone or in combination of two or more.

The aromatic polyamide has at least one nitro group as a functional group bonded to the aromatic ring. The nitro group of the aromatic polyamide is preferably an aromatic ring terminal group derived from a polyfunctional aromatic amine. By providing the aromatic polyamide with at least one nitro group, the oxidation resistance and acid resistance of the aromatic polyamide are improved.

In the method of imparting a nitro group to an aromatic polyamide, the polyfunctional aromatic amine or polyfunctional aromatic carboxylic acid constituting the monomer of the aromatic polyamide may have a nitro group itself, or the method of applying a chemical action to the aromatic polyamide thereafter may be employed. Examples of the method of applying the chemical action include oxidation treatment of a terminal amino group of the aromatic polyamide. Specifically, a water-soluble oxidizing agent is preferably brought into contact with the composite semipermeable membrane, and examples of the water-soluble oxidizing agent include hydrogen peroxide, peroxyacetic acid (peroxyacetic acid), sodium perborate, potassium peroxymonosulfate (potassium peroxymonosulfate), and the like.

When the number of nitrogen atoms derived from the nitro group in the aromatic polyamide is a and the total number of nitrogen atoms in the aromatic polyamide is B, when a and B are analyzed by X-ray photoelectron spectroscopy (XPS), the a/B value measured from one surface of the separation functional layer is different from the a/B value measured from the other surface. The larger the a/B of the surface on one side of the separation functional layer, the higher the oxidation resistance and acid resistance, and the smaller the a/B of the surface on the other side, the higher the alkali resistance and the higher the retention of the higher-order structure inherent in polyamide.

The inventors of the present application have found that a film excellent in all of oxidation resistance, acid resistance, and alkali resistance can be realized by setting the difference in a/B between the surface on one side and the surface on the other side of the separation functional layer to 0.010 or more. That is, when C is the A/B when X-rays are irradiated from one surface of the separation functional layer and D is the A/B when X-rays are irradiated from the other surface of the separation functional layer, the relationship of C-D ≧ 0.010 is preferably satisfied. The difference (C-D) is more preferably 0.030 or more. The difference (C-D) is preferably 0.20 or less.

Here, the surface on the side of the separation functional layer refers to the surface on which the composite semipermeable membrane is formed and the side on which raw water is supplied to the separation functional layer, and the surface on the other side refers to the surface in contact with the support membrane and is also referred to as the "back surface" with respect to the "front surface".

The ratio (a/B) of the number a of nitrogen atoms derived from the nitro group to the total number B of nitrogen atoms can be determined by X-ray photoelectron spectroscopy (XPS) analysis of the polyamide. Specifically, it can be determined by X-ray photoelectron spectroscopy (XPS) exemplified in "Journal of Polymer Science", Vol.26, 559-572(1988) and "Japan society of follow-up (Journal of Japan society of adhesion)", Vol.27, No.4 (1991). The a and B on the surface (surface) on the side of the separation functional layer can be measured by irradiating X-rays from the side where raw water is supplied to the separation functional layer. A and B of the other side (back side) of the separation functional layer can be measured as follows: the measurement is performed by peeling the base material from the composite semipermeable membrane, placing the separation functional layer on a substrate such that the front surface of the separation functional layer is in contact with the substrate (wetted with an alcohol such as ethanol), removing the porous supporting layer with an organic solvent such as methylene chloride, and irradiating X-rays with the back surface of the separation functional layer facing upward. The substrate used in this case is not particularly limited, and examples thereof include silicone resin and silicon wafer.

When the total number of nitrogen atoms B and the number of oxygen atoms E are measured by irradiating X-rays from the surface on the side where the functional layer is separated, a film having a more excellent balance among oxidation resistance, acid resistance, and alkali resistance can be obtained by satisfying E/B of 1.00. ltoreq.1.20.

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

Production method

Next, a method for producing a composite semipermeable membrane will be described with reference to specific examples.

The polyamide as the skeleton of the separation functional layer in the composite semipermeable membrane can be formed, for example, as follows: interfacial polycondensation is performed on the surface of the support film (on the surface of the porous support layer if the support film is provided with the substrate and the porous support layer) using an aqueous solution containing the above-described polyfunctional aromatic amine and an organic solvent (immiscible with water) solution containing the polyfunctional aromatic carboxylic acid derivative.

The concentration of the polyfunctional aromatic amine in the polyfunctional aromatic amine aqueous solution is preferably in the range of 0.1 to 20% by weight, more preferably in the range of 0.5 to 15% by weight. Within this range, sufficient desalting performance and water permeability can be obtained. The aqueous polyfunctional aromatic amine solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, and the like, as long as the reaction between the polyfunctional aromatic amine and the polyfunctional aromatic carboxylic acid derivative is not hindered. The surfactant has the effect of improving the wettability of the surface of the support film and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent. The organic solvent may function as a catalyst for the interfacial polycondensation reaction, and the addition of the organic solvent may allow the interfacial polycondensation reaction to proceed efficiently.

The concentration of the polyfunctional aromatic carboxylic acid derivative in the organic solvent solution is preferably in the range of 0.01 to 10% by weight, more preferably in the range of 0.02 to 2.0% by weight. This is because a sufficient reaction rate can be obtained by setting the concentration of the polyfunctional aromatic carboxylic acid derivative to 0.01 wt% or more, and the occurrence of side reactions can be suppressed by setting the concentration to 10 wt% or less. Further, it is more preferable to contain an acylation catalyst such as DMF in the organic solvent solution because interfacial polycondensation can be promoted.

The organic solvent is preferably immiscible with water, and is preferably inactive with the polyfunctional aromatic amine compound and the polyfunctional aromatic carboxylic acid derivative without damaging the porous support film, and can dissolve the polyfunctional aromatic carboxylic acid derivative. Preferable examples thereof include hydrocarbon compounds such as n-hexane, n-octane, isooctane and n-decane.

In order to perform interfacial polycondensation on the porous support film, first, the above-mentioned polyfunctional aromatic amine aqueous solution is brought into contact with the support film. The contact is preferably performed uniformly and continuously on the surface of the support film. Specifically, for example, a method of coating the support film with an aqueous solution of a polyfunctional aromatic amine or a method of immersing the support film in an aqueous solution of a polyfunctional aromatic amine may be mentioned. The contact time between the support film and the aqueous solution of the polyfunctional aromatic amine is preferably in the range of 1 to 10 minutes, more preferably in the range of 1 to 3 minutes.

After the aqueous solution of the polyfunctional aromatic amine is brought into contact with the support film, the liquid is drained sufficiently so that no droplets remain on the film. By sufficiently discharging the liquid, the following can be prevented: the droplet remaining part becomes a film defect after film formation, thereby causing a decrease in film performance. As a method of discharging liquid, for example, the following methods can be used: as described in japanese patent application laid-open No. 2-78428, a method of holding the support film in the vertical direction after contact with the aqueous solution of the polyfunctional aromatic amine to cause the excessive aqueous solution to flow down naturally, a method of blowing an air stream such as nitrogen from a nozzle to forcibly discharge the liquid, and the like. Further, after the liquid discharge, the membrane surface may be dried to remove a part of the water content of the aqueous solution.

The thus-obtained aqueous polyfunctional aromatic amine solution phase is brought into contact with an organic solvent solution containing a polyfunctional aromatic carboxylic acid derivative, and interfacial polycondensation is performed to form a skeleton of the crosslinked polyamide separation functional layer.

The method of contacting the organic solvent solution containing the polyfunctional aromatic carboxylic acid derivative with the aqueous polyfunctional aromatic amine solution may be performed in the same manner as the method of coating the support film with the aqueous polyfunctional aromatic amine solution.

At this time, the support film which has been brought into contact with the organic solvent solution of the polyfunctional aromatic acid halide may be heated. The temperature of the heat treatment is 50 ℃ to 180 ℃, preferably 60 ℃ to 160 ℃. By heating at 50 ℃ or higher, the reaction acceleration effect due to heat can be used to compensate for the decrease in reactivity accompanying the consumption of monomers in the interfacial polymerization reaction. By heating at 180 ℃ or lower, the solvent can be prevented from completely volatilizing, and the reaction efficiency can be prevented from remarkably decreasing. The heat treatment time is preferably 5 seconds to 180 seconds. By setting the time to 5 seconds or more, an effect of promoting the reaction can be obtained, and by setting the time to 180 seconds or less, the solvent can be prevented from completely volatilizing.

As described above, the separation functional layer containing the crosslinked polyamide can be formed on the support film by interfacial polycondensation by contacting the solution with the organic solvent containing the polyfunctional aromatic carboxylic acid derivative, and then draining the remaining solvent. As a method of draining, for example, a method of removing excess organic solvent by naturally flowing down while holding the film in a vertical direction can be employed. In this case, the time for holding in the vertical direction is preferably within a period of 1 to 5 minutes, and more preferably within a period of 1 to 3 minutes. If the length is too short, the separation functional layer is not completely formed, and if the length is too long, the organic solvent is excessively dried, defects are easily generated, and performance is easily lowered.

The composite semipermeable membrane obtained by the above method can further improve the solute rejection performance and water permeability of the composite semipermeable membrane by subjecting the composite semipermeable membrane to a hot water treatment step of treating the composite semipermeable membrane at 40 to 100 ℃, preferably 60 to 100 ℃ for 1 to 10 minutes, more preferably 2 to 8 minutes.

Next, a method of imparting a nitro group to an aromatic ring derived from a functional aromatic amine by applying a chemical action to the aromatic polyamide will be described.

There are two methods for providing a nitro group as an end group of a polyamide, one is a method of converting a terminal amino group, and the other is a method of substituting an unsubstituted aromatic ring, and the method of converting a terminal amino group is preferable in terms of easy conversion and easy control of the substitution position.

As a method for converting the terminal amino group into a nitro group, an oxidation reaction can be utilized. In the oxidation reaction, a common oxidizing agent such as a water-soluble peroxide can be used, but from the viewpoint of reactivity with the aromatic polyamide and ease of handling, the oxidizing agent is preferably a persulfate compound, and more preferably a potassium peroxymonosulfate salt.

The reaction means of the oxidizing agent and the polyamide is preferably, for example, a method in which an aqueous solution of the oxidizing agent is applied to a composite semipermeable membrane of polyamide, and the membrane is covered with the aqueous solution and left to stand, in order to increase the introduction rate of the nitro group into the surface of the separation functional layer and to form a distribution in the depth direction; a method of applying an aqueous solution of an oxidizing agent by spraying; and so on.

The concentration of the oxidizing agent is preferably 0.1 to 10% by weight, more preferably 0.5 to 3% by weight.

The pH of the aqueous oxidant solution is not particularly limited as long as the oxidizing ability of the oxidant is sufficiently exhibited, and is preferably in the range of 1.5 to 7.0.

The contact time of the aqueous oxidizing agent solution with the polyamide is preferably 30 seconds to 20 minutes, and more preferably 1 minute to 10 minutes, in order to maintain the nitrate group on the surface and the nitro group on the back surface (in contact with the support film) to be small.

The contact temperature of the aqueous oxidant solution and the polyamide is preferably 10 to 90 ℃, more preferably 40 to 60 ℃. By the temperature treatment, a state in which many nitro groups are present on the surface and few nitro groups are present on the inner and back surfaces can be realized in a short time, and a film having excellent oxidation resistance, acid resistance, and alkali resistance can be obtained.

After contacting with the oxidizing agent, the polyamide composite membrane is contacted with a reducing agent in order to stop the oxidation reaction. Here, the reducing agent is not particularly limited as long as it is a reagent that causes a redox reaction with the oxidizing agent used, and it is preferable to use any of sodium bisulfite, sodium sulfite, and sodium thiosulfate from the viewpoint of easy availability and easy handling. The reducing agent is preferably used in the form of a 0.01 to 1 wt% aqueous solution.

The time for contacting the reducing agent may be such that the oxidation reaction is stopped and the structure of the polyamide is not changed, and an immersion time of 30 seconds to 20 minutes is generally preferable.

After contacting with the reducing agent, it is preferable to wash the reducing agent remaining in the polyamide composite membrane with water.

The composite semipermeable membrane of the present invention thus formed can be suitably used in the form of a spiral composite semipermeable membrane element by being wound around a cylindrical water collecting pipe having a large number of holes formed therein together with a raw water passage member such as a plastic net, a permeated water passage member such as a tricot or the like, and a membrane for improving pressure resistance as required. Alternatively, the elements may be connected in series or in parallel and stored in a pressure vessel to produce a composite semipermeable membrane module.

The composite semipermeable membrane, or the elements and modules thereof may be combined with a pump for supplying raw water thereto, an apparatus for pretreating the raw water, and the like to constitute a fluid separation apparatus. By using this separation apparatus, raw water can be separated into permeated water such as drinking water and concentrated water that does not permeate through the membrane, and water that meets the target can be obtained.

When the operating pressure of the fluid separation apparatus is high, the salt rejection rate is improved, but when the energy required for operation is also increased and the durability of the composite semipermeable membrane is taken into consideration, the operating pressure when the water to be treated permeates through the composite semipermeable membrane is preferably 1.0MPa or more and 10MPa or less. The feed water temperature is preferably 5 ℃ or higher and 45 ℃ or lower because the desalination rate decreases as the feed water temperature increases, but the membrane permeation flux also decreases as the temperature decreases. In the case of feed water having a high salt concentration such as seawater, when the pH of the feed water is increased, scale such as magnesium may be generated, and operation at a high pH may cause deterioration of the membrane, and therefore, operation in a neutral region is preferable.

Examples of the raw water that can be treated by the composite semipermeable membrane according to the present invention include liquid mixtures containing 500mg/L to 100g/L of TDS (Total Dissolved Solids) such as seawater, brackish water, and waste water. By TDS is meant the total dissolved solids content, expressed as "weight per unit volume" or "weight ratio". By definition, the solution filtered using a 0.45 micron filter is evaporated at a temperature of 39.5 to 40.5 ℃ to calculate the TDS from the weight of the residue, and more simply, converted from the practical salinity (S).

The composite semipermeable membrane of the present invention is characterized by high oxidation resistance and acid resistance, and the index of oxidation resistance is preferably, for example, resistance to an aqueous sodium hypochlorite solution adjusted to a pH near neutrality (more specifically, pH6.0 to 8.0). This is because free chlorine generated from hypochlorous acid is a representative oxidizing substance contained in the raw water.

As the index of acid resistance and alkali resistance, resistance to an aqueous sulfuric acid solution having a pH of 1 and an aqueous sodium hydroxide solution having a pH of 13 are suitable. Since the conditions of pH1 and pH13 are severer than the pH at the time of acid washing and alkali washing during the membrane filtration operation, if the membranes exhibit resistance to an aqueous solution of sulfuric acid having a pH of 1 and an aqueous solution of sodium hydroxide having a pH of 13, the membranes are ensured to be less susceptible to deterioration even when acid washing and alkali washing are performed a plurality of times.

Examples

The present invention will be described in more detail below with reference to examples.

(1) Ratio A/B of the number of nitrogen atoms originating from nitro groups to the total number of nitrogen atoms in the aromatic polyamide

The number of nitrogen atoms (a) derived from the nitro group and the total number of nitrogen atoms (B) on the surface (front surface) on one side and the surface (back surface) on the other side of the separation functional layer of the composite semipermeable membranes of the comparative examples and examples were calculated from the measurement results by X-ray photoelectron spectroscopy (XPS).

A measuring device: quantera SXM (manufactured by PHI corporation)

Excitation of X-rays: monochromatic Al K alpha 1,2 ray (1486.6eV)

X-ray diameter: 0.2mm

The peak of N1s obtained by XPS is caused by the inner shell electrons of the nitrogen atom. In the following examples, the N1s peak is considered to be composed of a component derived from N-C and a component derived from NOx (x.gtoreq.2), and therefore the N1s peak was peak-divided based on 2 components. The component derived from N-C appeared at 400eV, and the component derived from NOx (x.gtoreq.2) appeared in the vicinity of 406 eV. The 2 nd position after the decimal point of the peak area ratio of each component was rounded and calculated. A/B was determined by dividing the peak area ratio derived from the NOx (x.gtoreq.2) group by the peak area ratio derived from N-C. When the peak separation result is 0.1% or less, the detection limit is regarded as being less than or equal to the detection limit. The surfaces a and B were analyzed by irradiating X-rays from the side where raw water was supplied to the composite semipermeable membrane. From the obtained results, the A/B of the surface was determined.

The analysis of the back surfaces a and B was performed as follows. The composite semipermeable membrane-released substrate was placed on a silicon wafer such that the surface of the separation functional layer was in contact with a 2cm square silicon wafer (which had been loaded with 1 drop of ethanol), and dichloromethane was repeatedly flowed over the silicon wafer until the elution of the polymer forming the porous support layer into a dichloromethane solution could no longer be detected by thin layer chromatography. X-rays were irradiated from the upper side of the thus obtained sample, and thereby a and B on the back surface of the separation functional layer were calculated. From the obtained results, A/B of the back surface was obtained.

Then, C-D, which is the difference between A/B on the front surface and A/B on the back surface, is calculated.

(2) E/B ratio of total number of nitrogen atoms B to total number of oxygen atoms E in aromatic polyamide

The composite semipermeable membranes of comparative examples and examples were irradiated with X-rays from the surface (front surface) on the side where the functional layer was separated under the same conditions as described in (1), and the total nitrogen number B and the total oxygen number E were calculated from the measurement results by X-ray photoelectron spectroscopy (XPS). E/B was calculated based on the intensity ratio of the N1s peak to the O1s peak obtained by XPS.

Various properties of the composite semipermeable membranes of comparative examples and examples were determined by the following methods: seawater (TDS concentration of about 3.5%) adjusted to 25 ℃ and ph6.5 was supplied to the composite semipermeable membrane at an operating pressure of 5.5MPa, and subjected to membrane filtration treatment to measure the quality of the permeated water and the supplied water.

(3) Membrane permeation flux

The membrane permeation flux (m) is expressed as a membrane permeation flux (m) in terms of the membrane permeation flux of feed water (seawater) per 1 square meter of membrane surface for 1 day (cubic meter)³/m²Day).

(4) Boron removal rate

The boron concentrations in the feed water and the permeated water were analyzed by an ICP emission spectrometer ("P-4010" (trade name) manufactured by Hitachi, Ltd. and determined by the following equation.

Boron removal rate (%) (100 × {1- (boron concentration in permeated water/boron concentration in feed water) }

(5) Oxidation resistance test

The composite semipermeable membrane was immersed in a 100mg/L aqueous sodium hypochlorite solution adjusted to pH6.5 at 25 ℃ for 20 hours. Then, the composite semipermeable membrane was immersed in a 100mg/L aqueous solution of sodium hydrogen sulfite for 10 minutes, washed sufficiently with water, and evaluated for the boron removal rate.

(6) Acid resistance test

The composite semipermeable membrane was immersed in an aqueous sulfuric acid solution adjusted to a pH of 1 at 25 ℃ for 20 hours. Then, the composite semipermeable membrane was sufficiently washed with water, and the boron removal rate was evaluated.

(7) Alkali resistance test

The composite semipermeable membrane was immersed in an aqueous sodium hydroxide solution adjusted to pH13 at 25 ℃ for 20 hours. Then, the composite semipermeable membrane was sufficiently washed with water, and the boron removal rate was evaluated.

(reference example 1)

A16.0 wt.% DMF solution of polysulfone (PSf) was cast at a thickness of 200 μm at 25 ℃ onto a polyester nonwoven fabric (air permeability of 2.0 cc/cm)²Second), the membrane was immediately immersed in pure water and left to stand for 5 minutes, thereby producing a porous support membrane.

(examples 1 and 2)

The porous support film obtained by reference example 1 was immersed in a 3 wt% aqueous solution of M-phenylenediamine (M-PDA) for 2 minutes, the support film was slowly lifted in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and then Isoper M (manufactured by Exxon mobile Corporation) containing trimesoyl chloride (TMC)0.165 wt% at 25 ℃ was coated in such a manner that the surface was completely wetted, and after standing for 1 minute, the film was made to stand to drain and remove excess solution, thereby obtaining a composite semipermeable membrane.

On the membrane surface of the obtained composite semipermeable membrane at 60 deg.C at 0.33L/m²A3 wt% aqueous solution of potassium peroxymonosulfate salt at the specified pH (example 1: pH3, example 2: pH2) was applied to the film, and the film was allowed to stand in an oven at 60 ℃ for the specified time (example 1: 10 minutes, example 2: 2 minutes) (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

With respect to the obtained composite semipermeable membrane, the difference (C-D) between a/B on the front surface and the back surface of the separation functional layer was calculated by the method described in (1) above, and the ratio E/B of the total number of oxygen atoms E to the total number of nitrogen atoms B of the separation functional layer was calculated by the method described in (2) above. The membrane permeation flux and the boron removal rate of the obtained composite semipermeable membrane were measured by the methods (3) and (4), and the boron removal rate was measured by the methods (5) to (7) by performing the oxidation resistance, acid resistance, and alkali resistance tests of the composite semipermeable membrane. The results are shown in Table 2.

(examples 3 to 5)

The porous support film obtained in reference example 1 was immersed in a 3 wt% aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes, the support film was slowly lifted up in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and then isooctane at 25 ℃ containing 0.165 wt% of trimesoyl chloride (TMC) was coated so as to completely wet the surface, and after leaving for 10 seconds, the membrane was left to stand in an oven at 120 ℃ for 15 seconds, thereby obtaining a composite semipermeable membrane. The film surface of the obtained composite semipermeable membrane was heated at a predetermined temperature (example 3: 90 ℃, example 4 and example 5: 60 ℃) to 0.33L/m²The aqueous solution of potassium peroxymonosulfate salt at a predetermined concentration of pH3 (example 3: 3 wt%, examples 4 and 5: 1 wt%) was coated on the film, and the film was allowed to stand in an oven at the same temperature as that for coating for a predetermined period of time (example 3, example 4: 5 minutes, example 5: 2 minutes) (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

The C-D and E/B of the separation functional layer were calculated for the obtained composite semipermeable membrane, and the membrane permeation flux and boron removal rate of the obtained composite semipermeable membrane were measured, and the oxidation resistance, acid resistance, and alkali resistance of the composite semipermeable membrane were tested to measure the boron removal rate. The results are shown in Table 2.

(examples 6 to 8)

The porous support film obtained by reference example 1 was immersed in a 3 wt% aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes, the support film was slowly lifted up in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and decane at 25 ℃ containing 0.165 wt% of trimesoyl chloride (TMC) was applied so as to completely wet the surface, and after leaving to stand for 10 seconds, the film was left to stand in an oven at 120 ℃ for 15 seconds, thereby obtaining a composite semipermeable membrane.

The resulting composite semipermeable membrane was heated to a predetermined temperature on the membrane surface (examples 6 and 7: 60 ℃ C., examples)8: 40 ℃) at 0.33L/m²Coating a 1 wt% potassium peroxymonosulfate aqueous solution at a predetermined pH (example 6: pH6, example 7 and example 8: pH2) to cover the film, and leaving the film in an oven at the same temperature as the coating for a predetermined time (examples 6 and 7: 2 minutes, example 8: 5 minutes) (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

Comparative examples 1 and 2

The porous support film obtained by reference example 1 was immersed in a 3 wt% aqueous solution of M-phenylenediamine (M-PDA) for 2 minutes in a manner similar to that described in international publication No. 2011/105278, the support film was slowly lifted in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and then Isoper M (manufactured by Exxon mobile Corporation) at 25 ℃ containing 0.165 wt% of trimesoyl chloride (TMC) was applied in such a manner that the surface was completely wetted, and after standing for 1 minute, the film was made to stand to drain and remove excess solution, thereby obtaining a composite semipermeable membrane.

The resulting composite semipermeable membrane was immersed in a 1 wt% potassium peroxymonosulfate aqueous solution at a predetermined pH (comparative example 1: pH6, comparative example 2: pH2) at 25 ℃ for 30 minutes (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

The C-D and E/B of the separation functional layer were calculated for the obtained composite semipermeable membrane, and the membrane permeation flux and boron removal rate of the obtained composite semipermeable membrane were measured, and the boron removal rate was measured by performing oxidation resistance, acid resistance, and alkali resistance tests. The results are shown in Table 2.

Comparative example 3

The porous support film obtained by reference example 1 was immersed in a 3 wt% aqueous solution of M-phenylenediamine (M-PDA) for 2 minutes, the support film was slowly lifted in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and then Isoper M (manufactured by Exxon Mobil Corporation) containing trimesoyl chloride (TMC)0.165 wt% at 25 ℃ was coated in such a manner that the surface was completely wetted, left to stand for 10 seconds, and then left to stand in an oven at 25 ℃ for 1 minute, thereby obtaining a composite semipermeable membrane.

On the membrane surface of the obtained composite semipermeable membrane at 25 deg.C at 0.33L/m²The film was covered with a 1% by weight aqueous solution of peracetic acid, and the film was left to stand in an oven at 25 ℃ for 60 minutes. Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

Comparative examples 4 and 5

The porous support film obtained in reference example 1 was immersed in a 3 wt% aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes, the support film was slowly lifted up in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and then isooctane at 40 ℃ containing 0.165 wt% of trimesoyl chloride (TMC) was coated so as to completely wet the surface, and after leaving for 10 seconds, the membrane was left to stand in an oven at 120 ℃ for 1 minute, whereby a composite semipermeable membrane was obtained.

The resulting composite semipermeable membrane was immersed in a 1 wt% potassium peroxymonosulfate aqueous solution at a predetermined pH (example 4: pH8, example 5: pH6) at 25 ℃ for a predetermined period of time (comparative example 4: 30 minutes, comparative example 5: 2 minutes) (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

Comparative example 6

The porous support film obtained by reference example 1 was immersed in a 3 wt% aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes, the support film was slowly lifted up in the vertical direction, nitrogen gas was blown from a gas nozzle and excess aqueous solution was removed from the surface of the support film, and decane at 40 ℃ containing 0.165 wt% of trimesoyl chloride (TMC) was applied so as to completely wet the surface, and after leaving to stand for 10 seconds, the film was left to stand in an oven at 120 ℃ for 15 seconds, thereby obtaining a composite semipermeable membrane.

The resulting composite semipermeable membrane was immersed in a 1 wt% potassium peroxomonosulfate aqueous solution at pH3 for 2 minutes at 60 deg.C (see Table 1). Then, the membrane was immersed in a 0.1 wt% aqueous solution of sodium hydrogen sulfite for 10 minutes, and then washed with water to obtain a composite semipermeable membrane.

The C-D and E/B of the separation functional layer were calculated for the obtained composite semipermeable membrane, and the membrane permeation flux and boron removal rate of the obtained composite semipermeable membrane were measured, and the oxidation resistance, acid resistance, and alkali resistance of the composite semipermeable membrane were further tested to measure the boron removal rate. The results are shown in Table 2.

[ Table 1]

[ Table 2]

As is clear from the results shown in Table 2, in examples 1 to 8, C-D was 0.010 or more. These composite semipermeable membranes were found to have high chemical resistance suitable for practical use, as they were maintained at a boron removal rate of 85% or more after the forced deterioration test with chlorine and at a boron removal rate of 90% or more after the forced deterioration test with acid or alkali.

Although the present invention has been described in detail or with reference to specific embodiments, it will be apparent to those skilled in the art that various changes or modifications may be made without departing from the spirit and scope of the invention. The basic application of the present application is japanese patent application filed on 25.12.2015 (japanese patent application 2015) -254749), the contents of which are incorporated herein by reference.

Industrial applicability

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

Claims

1. A composite semipermeable membrane comprising a support membrane and a separation functional layer provided on the support membrane, wherein,

the separation functional layer contains an aromatic polyamide which is a polymer of a polyfunctional aromatic amine and a polyfunctional aromatic carboxylic acid derivative, the aromatic polyamide having a nitro group as a functional group bonded to an aromatic ring,

wherein the number of nitrogen atoms originating from a nitro group in the aromatic polyamide is A, the number of total nitrogen atoms in the aromatic polyamide is B, and when A and B are analyzed by X-ray photoelectron spectroscopy (XPS), when A/B when X-rays are irradiated from one surface of the separation functional layer is C and A/B when X-rays are irradiated from the other surface of the separation functional layer is D, C-D of the separation functional layer is 0.010 or more, and,

the other side surface of the separation functional layer is in contact with the support film.

2. The composite semipermeable membrane according to claim 1, wherein when the analysis is performed by irradiating X-rays from the surface on the one side of the separation functional layer by the X-ray photoelectron spectroscopy (XPS), when the total number of oxygen atoms in the polyamide is defined as E, E/B is 1.00. ltoreq. E/1.20.

3. The composite semipermeable membrane according to claim 1, wherein C-D is 0.20 or less.

4. The composite semipermeable membrane according to claim 2, wherein C-D is 0.20 or less.

5. The composite semipermeable membrane according to claim 1, wherein C-D is 0.030 or more.

6. The composite semipermeable membrane according to claim 2, wherein C-D is 0.030 or more.

7. The composite semipermeable membrane according to claim 3, wherein C-D is 0.030 or more.

8. The composite semipermeable membrane according to claim 4, wherein C-D is 0.030 or more.

9. The composite semipermeable membrane according to any of claims 1 to 8, which is used for treating a liquid mixture having TDS (total dissolved solids) of 500mg/L to 100 g/L.

10. A composite semipermeable membrane element comprising the composite semipermeable membrane according to any one of claims 1 to 9.