WO2021192816A1

WO2021192816A1 - Composite semipermeable membrane

Info

Publication number: WO2021192816A1
Application number: PCT/JP2021/007394
Authority: WO
Inventors: 清彦高谷; 芳機西口; 雅美尾形
Original assignee: 東レ株式会社
Priority date: 2020-03-25
Filing date: 2021-02-26
Publication date: 2021-09-30
Also published as: JPWO2021192816A1

Abstract

The present invention relates to a composite semipermeable membrane which is provided with a base material, a porous supporting body that is arranged on the base material, and a separation functional layer that is arranged on the porous supporting body, wherein: the porous supporting body contains a copolymer of a vinyl cyanide monomer and an aromatic vinyl monomer; and with respect to a film that is obtained by dissolving the porous supporting body into a solvent and drying the resulting solution, the cyano group ratio shown below and expressed by the absorption intensity of the infrared absorption spectrum as measured by means of a Fourier transform infrared spectrophotometer is from 0.20 to 0.85.　Cyano group ratio = (absorption intensity at 2,240 cm-1)/(absorption intensity at 1,605 cm-1)

Description

Composite semipermeable membrane

The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture and a method for producing the same. The composite semipermeable membrane obtained by the present invention can be suitably used for, for example, desalination of brackish water and purification of tap water.

Regarding the separation of the mixture, there are various techniques for removing substances (for example, salts) dissolved in a solvent (for example, water). In recent years, the use of membrane separation methods has been expanding as a process for energy saving and resource saving. 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, when obtaining drinking water from seawater, brackish water, water containing harmful substances, manufacturing ultrapure water for industrial use, wastewater treatment, recovery of valuable resources, purification of tap water, etc. There is.

Most of the filtration membranes currently on the market, especially reverse osmosis membranes and nanofiltration membranes, are composite semipermeable membranes. Patent Document 1 discloses a composite semipermeable membrane including a support membrane including a base material and a porous support, and a separation functional layer provided on the porous support. Further, as the thermoplastic resin contained in the porous support, polysulfone, polyacrylamide, polyethersulfone, cellulose ester, polyacrylonitrile, polyvinyl chloride and the like are disclosed. Patent Document 2 discloses a copolymer based on polyacrylonitrile as a material for a support.

International Publication No. 2014/192883 U.S. Patent Application Publication No. 2012/181228

An object of the present invention is to improve water permeability in a composite semipermeable membrane provided with a porous support containing a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer.

In order to achieve the above object, the present invention has the following configuration.
[1] A composite semipermeable membrane comprising a base material, a porous support arranged on the base material, and a separation functional layer arranged on the porous support.
The porous support contains a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer.
For the film obtained by dissolving and drying the porous support in a solvent, the following cyano group ratio represented by the absorption intensity of the infrared absorption spectrum measured by the Fourier transform infrared spectrophotometer is 0.20 or more and 0. A composite semipermeable membrane of .85 or less.
Cyan group ratio = 2240 cm ^-1 absorption intensity / 1605 cm ^-1 absorption intensity [2] The composite semipermeable membrane according to the above [1], wherein the cyano group ratio is 0.40 or more and 0.78 or less.
[3] The composite semipermeable membrane according to the above [2], wherein the cyano group ratio is 0.40 or more and 0.62 or less.
[4] The composite semipermeable membrane according to any one of [1] to [3], wherein the weight average molecular weight Mw of the copolymer is 220,000 or more and 1,000,000 or less.
[5] The composite semipermeable membrane according to the above [4], wherein the weight average molecular weight Mw of the copolymer is 260,000 or more and 1,000,000 or less.

The porous support contains a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer, and the cyano group ratio of the porous support is 0.20 or more and 0.85 or less. Therefore, the composite semipermeable membrane has high water permeability (permeation flow velocity: Flux).

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following description, and can be arbitrarily modified and carried out without departing from the gist of the present invention.
Further, in the present specification, "% by weight", "parts by weight" and "ppm by weight" are synonymous with "% by mass", "parts by mass" and "ppm by mass", respectively, and are simply expressed as ppm. Means that the weight is ppm.

1. 1. Composite Semipermeable Membrane The composite semipermeable membrane described below includes a base material, a porous support arranged on the base material, and a separation functional layer arranged on the porous support. The complex of the base material and the porous support is hereinafter referred to as "support film".
The separation functional layer has substantially the ion separation performance, and the support membrane has substantially no separation performance, but the support membrane can impart strength to the composite semipermeable membrane.

(1-1) Support film (1-1-1) Base material Examples of the base material include polyester-based polymers, polyamide-based polymers, polyolefin-based polymers, and mixtures and copolymers thereof. Among them, a polyester-based polymer fabric having high mechanical and thermal stability is particularly preferable as the base material. As the cloth, a non-woven fabric, a woven fabric, or a knitted fabric is preferable. The non-woven fabric may be either a long-fiber non-woven fabric or a short-fiber non-woven fabric. The long fiber non-woven fabric preferably has, for example, an average fiber length of 300 mm or more and an average fiber diameter of 3 to 30 μm.

The thickness of the base material is preferably 20 μm or more and 200 μm or less, more preferably 40 μm or more, and further preferably 120 μm or less. The thickness of the substrate is specifically the arithmetic mean of the thickness measured at any 20 locations on the substrate by a dial or digital thickness gauge. However, if it is difficult to measure the thickness of the base material with a thickness gauge, it may be measured with an optical microscope or a scanning electron microscope.

(1-1-2) Porous Support In the present invention, the porous support contains a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer (that is, a vinyl-based copolymer). ..

The cyano group ratio measured for the film made from the porous support is preferably 0.85 or less, more preferably 0.78 or less, still more preferably 0.62 or less. The cyano group ratio is preferably 0.20 or more, or 0.40 or more.
The "film made from a porous support" refers to a film obtained by dissolving and drying the porous support in a solvent, and specifically, by dissolving the porous support in a solvent. It is a film obtained by evaporating a solvent from the obtained solution (that is, drying the solution).

The cyano group ratio in this film represents the average cyano group ratio in the entire porous support. Therefore, in the following, "the ratio of cyano groups measured for a film made from a porous support" will be referred to as "the ratio of cyano groups in a porous support".

As a result of diligent studies, the present inventors have found that the composite semipermeable membrane exhibits high water permeability when the ratio of cyano groups in the porous support is within the above range. The reason for the improvement in water permeability is not clear, but the relatively low proportion of cyano groups increases the hydrophobicity of the porous support, and the polyfunctional amine is sufficient when forming the separation functional layer by interfacial polycondensation. This is thought to be because it becomes easier to supply and the folds in the separation function layer grow larger.

The details of the method for measuring the cyano group ratio are as follows. First, the support membrane or the composite semipermeable membrane is washed with warm water and air-dried at room temperature. Next, only the porous support is dissolved by the solvent. Acetone or DMF is preferable as the solvent. The base material and the separating functional layer are removed by filtering the obtained solution through a metal mesh (wire diameter 0.03 mm, 300 mesh). Subsequently, the solvent is removed from the obtained filtrate using an evaporator or the like to obtain an insoluble matter. The insoluble matter is re-dissolved in a solvent so as to be about 10% by weight, and the solution obtained by using an applicator is applied on a glass substrate to a thickness of 15 mil (381 μm). The solvent is evaporated by leaving the glass substrate in an atmosphere of a temperature of 25 ° C. and a humidity of 50% for 12 hours or more to obtain a film-like sample. The obtained sample is dried in a vacuum dryer at 60 ° C. for 5 hours to completely remove the solvent, and the dried sample is subjected to absorbance analysis by a transmission method with a Fourier transform infrared spectrophotometer (FT-IR). From the absorption intensity of the following peaks appearing in the obtained infrared absorption spectrum, the cyano group ratio can be obtained from the following formula (1).
1605cm ^-1 : Peak attributed to vibration of benzene nucleus 2240cm ^-1 : Peak attributed to -CN expansion and contraction cyano group ratio = 2240cm ^-1 absorption intensity / 1605cm ^-1 absorption intensity (1)
As the FT-IR, IR Traxer-100 manufactured by Shimadzu Corporation or the like can be used.

Examples of the vinyl cyanide-based monomer include acrylonitrile, meta-acrylonitrile, and eta-acrylonitrile. The vinyl cyanide-based monomer is preferably acrylonitrile. The vinyl cyanide-based monomer contained in the copolymer may be one kind or two or more kinds.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, t-butylstyrene, o-ethylstyrene, o-chlorostyrene, o, p-dichlorostyrene and the like. Can be mentioned. The aromatic vinyl-based monomer is preferably styrene and α-methylstyrene, and more preferably styrene. The aromatic vinyl-based monomer contained in the copolymer may be one kind or two or more kinds.
The copolymer of the vinyl cyanide-based monomer and the aromatic vinyl-based monomer is preferably a copolymer of acrylonitrile and styrene.

The proportion of the vinyl cyanide-based monomer in the vinyl-based monomer constituting the vinyl-based copolymer is preferably 8% by weight or more and 20% by weight or less, and more preferably 10% by weight or more and 20% by weight or less. Is. When this ratio is 8% by weight or more, it is easy to obtain a porous support that can withstand the pressure at the time of practical use in water treatment or the like, which is preferable. Further, when this ratio is 20% by weight or less, the cyano group ratio can be easily set to 0.85 or less, which is preferable.

The proportion of the aromatic vinyl-based monomer in the vinyl-based monomer constituting the vinyl-based copolymer is preferably 80% by weight or more and 92% by weight or less, and more preferably 80% by weight or more and 90% by weight or less. Is.

The weight average molecular weight (Mw) of the tetrahydrofuran (THF) -soluble component in the porous support is the copolymer of the vinyl cyanide-based monomer and the aromatic vinyl-based monomer contained in the porous support. The value is the same as the weight average molecular weight (Mw). The value of such a weight average molecular weight (Mw) is preferably 220,000 or more, more preferably 260,000 or more, and further preferably 300,000 or more. When Mw is 220,000 or more, the pressure resistance of the porous support can be improved. Further, Mw is preferably 1,000,000 or less. When Mw is 1,000,000 or less, the moldability of the porous support is improved.

The weight average molecular weight (Mw) of the THF-soluble component in the porous support can be measured by the following method. First, the support membrane or composite semipermeable membrane cut into a predetermined area is thoroughly washed with warm water and air-dried at room temperature. Next, only the porous support is dissolved by contacting with THF, and the obtained solution is filtered through a metal mesh (wire diameter 0.03 mm, mesh 300, manufactured by Kansai Wire Mesh Co., Ltd.) to separate the base material. Remove the functional layer. Subsequently, the obtained filtrate is centrifuged at 8800 rpm (10,000 G or more) for 40 minutes, and then the supernatant is separated. The obtained supernatant is measured by gel permeation chromatography (GPC) using THF as a solvent and polystyrene as a standard substance to determine the weight average molecular weight.

The porous support may contain, for example, another thermoplastic resin in addition to the vinyl-based copolymer. A thermoplastic resin is a chain polymer, which has the property of being deformed or fluidized by an external force when heated. As the other thermoplastic resin, those having high compatibility with vinyl-based copolymers are preferable, and for example, polyvinyl chloride, polymethylmethacrylate, polyethylmethacrylate, polyethylene glycol, polyethylene oxide, polycarbonate, polylactic acid, and polyvinyl chloride. Examples thereof include acetate, polyethylene terephthalate, polyurethane, styrene-based copolymer, polybenzobisoxazole, polyvinylimidazole and polyphenylene sulfide. Here, the styrene-based copolymer is, for example, a random copolymer having a styrene skeleton, a block copolymer, a graft copolymer, or the like. Specific product names include, for example, Modiper CL430-G and CL130-D manufactured by NOF CORPORATION, Epocross RPS-1005 manufactured by Nippon Shokubai Co., Ltd., Polyimide PSX0371 and the like.

The thickness of the porous support is preferably 10 μm or more and 100 μm or less. When it is 10 μm or more, it is easy to suppress that the base material is exposed and defects occur, and when it is 100 μm or less, it is possible to suppress that the water permeability is deteriorated due to the resistance due to the thickness of the porous support.

The thickness of the porous support includes the type of solvent that dissolves the material used when forming the porous support, the viscosity of the solution containing the material, the concentration of the material in the solution, the coagulation bath temperature, the thickness of the solution applied to the substrate, etc. Can be controlled with.

The thickness of the porous support can be measured by cross-sectional observation with a scanning electron microscope (SEM), an optical microscope, or the like. When measuring by SEM, it can be obtained by the following method.
A section sample is prepared by cutting the composite semipermeable membrane or the support membrane by a freeze-cutting method, and the section sample is cross-sectionally observed by SEM at a magnification of 100 to 500 times. Measure the thickness of any 10 points using a scale or caliper. It is advisable to measure the thickness at 10 points at intervals of 10 μm in the direction perpendicular to the thickness direction of the film (plane direction of the film). The same operation is performed on 5 section samples, and the arithmetic mean of 50 data is calculated to obtain the thickness of the porous support. Before observing with SEM, the sample is thinly coated with platinum or platinum-palladium or ruthenium tetroxide. As the SEM, an S-5500 scanning electron microscope manufactured by Hitachi High-Technologies Corporation can be used, and observation is performed at an acceleration voltage of 3 to 6 kV.

The thickness of the support film and the porous support can also be measured by a thickness gauge as in the case of the base material. Since the thickness of the separating functional layer is very thin compared to the base material and the porous support, the thickness of the composite semipermeable membrane can be regarded as the total thickness of the base material and the porous support (thickness of the support membrane). can. Therefore, the thickness of the porous support can be easily calculated by measuring the thickness of the composite semipermeable membrane with a thickness gauge and subtracting the thickness of the base material from the thickness of the composite semipermeable membrane. When using a thickness gauge, the thickness is measured at any 20 points and the arithmetic mean is calculated.

The thickness of the support membrane (total thickness of the base material and the porous support) 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 support membranes is preferably 30 μm or more, more preferably 80 μm or more, and preferably 300 μm or less, more preferably 200 μm or less. Is.

(1-2) Separation Function Layer The separation function layer preferably has, for example, a thin film containing polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide as a main component. The main component refers to a component that occupies 50% by mass or more of the components of the separation functional layer. The ratio of polyamide in the separation functional layer may be 90% by mass or more, or the separation functional layer may be composed only of polyamide.

The separation functional layer can be formed, for example, by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide.
Here, it is preferable that at least one of the polyfunctional amine and the polyfunctional acid halide contains a trifunctional or higher functional compound.

The polyfunctional amine means an amine having two or more amino groups of at least one of a primary amino group and a secondary amino group in one molecule.
Examples of the polyfunctional amine include piperazine, 2,5-dimethylpiperazin, 2-methylpiperazin, 2,6-dimethylpiperazin, 2,3,5-trimethylpiperazin, 2,5-diethylpiperazin, 2,3,5. Aliphatic polyfunctional amines such as -triethylpiperazine, 2-n-propylpiperazine, 2,5-di-n-butylpiperazine and ethylenediamine; o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylene Two amino groups such as amine, m-xylylene diamine, p-xylylene diamine, o-diaminopyridine, m-diaminopyridine and p-diaminopyridine are in the ortho-, meta-position or para-position. Polyfunctional aromatic amines attached to the aromatic ring in relation; 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine and 4-amino Examples include polyfunctional aromatic amines such as benzylamine.

Among them, as the polyfunctional amine, piperazine, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, and 2-methylpiperazine are selected in consideration of the selective separability, permeability, and heat resistance of the membrane. It is preferably used. These polyfunctional amines may be used alone or in combination of two or more.

The polyfunctional acid halide refers to an acid halide having at least two carbonyl halide groups in one molecule.
For example, examples of the trifunctional acid halide include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride and 1,2,4-cyclobutanetricarboxylic acid trichloride. Examples of the bifunctional acid halide include aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride and naphthalenedicarboxylic acid chloride, adipoil chloride and sebacoil chloride. Examples thereof include aliphatic bifunctional acid halides and alicyclic bifunctional acid halides such as cyclopentanedicarboxylic acid dichloride, cyclohexanedicarboxylic acid dichloride and tetrahydrofuran dicarboxylic acid dichloride.

Considering the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional aromatic acid chloride. Further, considering the selective separability and heat resistance of the film, the polyfunctional acid halide is preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. The polyfunctional acid halide is particularly preferably trimesic acid chloride, terephthalic acid chloride, or isophthalic acid chloride because it is easily available and handled. In forming the separation functional layer, only one kind of polyfunctional aromatic acid halide may be used, or two or more kinds of polyfunctional aromatic acid halides may be combined.

The thickness of the separating functional layer is preferably 0.01 μm or more, more preferably 0.1 μm or more. The thickness is preferably 1 μm or less, more preferably 0.5 μm or less. Examples of the method for measuring the thickness of the separation functional layer include a method using a cross-sectional image obtained by a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and a method using an atomic force microscope (AFM).
The pore size of the separation function layer is, for example, preferably 2 nm or less, and more preferably 1 nm or less.

2. Method for manufacturing composite semipermeable membrane A method for manufacturing a composite semipermeable membrane will be described. The manufacturing method includes, for example, a step of forming a support film and a step of forming a separation functional layer. The composite semipermeable membrane of the present invention is not limited to the production method and the method for forming each layer described in the present specification.
The method for producing a composite semipermeable membrane includes, for example, the following steps (a) to (c).
(A) A step of arranging a solution in which a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer is dissolved in a good solvent on a substrate.
(B) A step of forming a porous support containing the copolymer by bringing the solution into contact with a coagulation bath containing the non-solvent of the copolymer.
(C) A step of forming a separation functional layer on the porous support.
The manufacturing method including the steps represented by these (a) to (c) is divided into a support film forming step and a separating functional layer forming step, and details are shown below.

(2-1) Support Film Forming Step The support film forming step preferably includes the above steps (a) and (b).

The preferred embodiment of the chemical structure of the copolymer (vinyl-based copolymer) in the above step (a) is as described above.

The copolymer concentration in the solution (hereinafter, may be referred to as "copolymer solution") in the above step (a) is preferably 10% by weight or more, and more preferably 14% by weight or more. The copolymer concentration is preferably 25% by weight or less, more preferably 22% by weight or less. When the copolymer concentration is 10% by weight or more and 25% by weight or less, a support film having strength enough to withstand practical use can be easily obtained, which is preferable.

The good solvent in the above step (a) preferably has a polar term dP of 11.0 or more and 17.0 or less in the Hansen solubility parameter, and preferably has a hydrogen bond term dH of 7.0 or more and 12.0 or less. Is. The good solvent is one that dissolves a vinyl-based copolymer and a thermoplastic resin.

Examples of the good solvent include N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF) and the like, and DMF is preferable.
Further, the good solvent may be a mixed solvent, and a mixture of DMSO and DMF is preferably used as the mixed solvent.

The copolymer solution may contain, for example, another thermoplastic resin in addition to the vinyl-based copolymer. When the solution contains another thermoplastic resin, the concentration of the other thermoplastic resin in the solution is preferably 1.0 to 20.0 parts by weight with respect to 100 parts by weight of the vinyl copolymer, more preferably. Is 3.0 to 15.0 parts by weight.

The copolymer solution may contain an additive for adjusting the pore size, porosity, hydrophilicity, elastic modulus, etc. of the porous support. Additives for adjusting the pore size and porosity include water-soluble polymers such as water, alcohols, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol and polyacrylic acid or salts thereof, as well as lithium chloride, sodium chloride and chloride. Examples thereof include inorganic salts such as calcium and lithium nitrate, formamide, and the like, but the additives are not limited thereto. Examples of the additive for adjusting the hydrophilicity and elastic modulus include various surfactants.
By mixing these materials, a copolymer solution can be prepared.

In the step of arranging the copolymer solution on the base material, for example, a spin coater, a flow coater, a roll coater, a spray, a comma coater, a bar coater, a gravure coater, a slit die coater and the like can be used.

The temperature of the solution when the copolymer solution is applied (arranged) is preferably in the range of 5 to 60 ° C, more preferably 10 ° C or higher, and more preferably 40 ° C or lower. When the temperature of the solution is within this range, the copolymer is not precipitated, and the copolymer solution is sufficiently impregnated between the fibers of the base material and then easily solidified. As a result, it is possible to obtain a support film in which the porous support is firmly bonded to the base material due to the anchor effect.

By applying the copolymer solution to the base material, the copolymer solution is impregnated in the base material. By controlling the impregnation of the copolymer solution into the base material, the occurrence of defects can be suppressed. In order to control the impregnation of the copolymer solution into the base material, for example, the time from the application of the copolymer solution on the base material to the immersion in the coagulation bath can be controlled, or the copolymer can be controlled. The viscosity can be adjusted by controlling the temperature or concentration of the solution, and these conditions can be combined.

In the above step (b), the time from applying (arranging) the copolymer solution on the substrate to immersing it in the coagulation bath is preferably in the range of, for example, 0.1 to 10 seconds. If the time required for immersion in the coagulation bath is within this range, the copolymer solution is sufficiently impregnated between the fibers of the base material and then easily solidified. The preferable range of the time until immersion in the coagulation bath may be appropriately adjusted depending on the viscosity of the copolymer solution to be used.

The coagulation bath in the step (b) preferably contains a non-solvent having a lower solubility than a good solvent of the copolymer.
Examples of the non-solvent include water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol and the like. Glycols, aromatic hydrocarbons, aliphatic alcohols, or mixed solvents thereof and the like. Water is generally used as the non-solvent.

The temperature of the coagulation bath is preferably −20 ° C. or higher, more preferably 0 ° C. or higher, and preferably 50 ° C. or lower, more preferably 40 ° C. or lower. By setting the temperature to 50 ° C. or lower, vibration of the coagulation bath surface due to thermal motion can be suppressed, and the smoothness of the film surface after film formation is likely to be improved. Further, when the temperature is set to −20 ° C. or higher, the solidification rate becomes sufficient for phase separation, and the film forming property is likely to be improved.

Next, it is preferable to wash the support film obtained above with water in order to remove the solvent remaining in the support film. The temperature of water at this time is preferably, for example, 25 to 90 ° C.

Next, a method for producing a copolymer (vinyl-based copolymer) constituting the porous support will be described.
As a method for producing a vinyl-based copolymer, for example, any polymerization method such as emulsion polymerization, suspension polymerization, bulk polymerization and solution polymerization can be used. As a method for producing a vinyl-based copolymer, two or more of these may be combined. Further, there is no particular limitation on the method of charging each monomer, and the initial batch charging or a part or all of the charged monomer is continuously or divided and polymerized in order to know the composition distribution of the copolymer. You may. As a method for producing a vinyl-based copolymer, a suspension polymerization method or a bulk polymerization method is preferable, and the suspension polymerization method is most preferable in consideration of easiness of polymerization control and easiness of post-treatment.

Examples of the suspension stabilizer used for suspension polymerization include inorganic suspension stabilizers such as clay, barium sulfate and magnesium hydroxide, polyvinyl alcohol, carboxymethyl cellulose, polyacrylamide, methyl methacrylate / acrylamide copolymer and the like. Examples include organic suspension stabilizers. Two or more of these may be used. Among these, an organic suspension stabilizer is preferable in terms of thermal coloration stability at the time of melting, and a methyl methacrylate / acrylamide copolymer is more preferable.

The initiator used for the polymerization is not particularly limited, and for example, peroxides, azo compounds, persulfates and the like are used.

Specific examples of peroxides include benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, t-butyl peroxyacetate, and t-butyl peroxybenzoate. t-Butylisopropylcarbonate, di-t-butyl peroxide, t-butylperoctate, 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t) -Butyl peroxy) Cyclohexane and t-butyl peroxy-2-ethylhexanoate and the like can be mentioned.

Specific examples of the azo compound include azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, 2-cyano-2-propylazo). Formamide, 1,1'-azobiscyclohexane-1-carbonitrile, azobis (4-methoxy-2,4-dimethylvaleronitrile), dimethyl 2,2'-azobisisobutyrate, 1-t-butylazo-2 Examples thereof include -cyanobutane and 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane.

Specific examples of persulfate include potassium persulfate, sodium persulfate, ammonium persulfate and the like.

Two or more of these initiators may be used. In addition, a redox-based initiator can also be used.

When the vinyl-based copolymer is produced by suspension polymerization, the polymerization temperature is not particularly limited, but from the viewpoint that the weight average molecular weight of the vinyl-based copolymer can be easily adjusted within the above range, and from the viewpoint of suspension stability. It is preferable to start the polymerization at 60 to 80 ° C., start the temperature rise when the polymerization rate reaches 50 to 70%, and finally reach 100 to 120 ° C.

The weight average molecular weight of the vinyl-based copolymer can be easily adjusted by using the above-mentioned initiator and chain transfer agent, setting the polymerization temperature within the above-mentioned preferable range, and the like.

Specific examples of the chain transfer agent include mercaptans such as n-octyl mercaptan, t-dodecyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan and n-octadecyl mercaptan, and terpenes such as terpinolen. As the chain transfer agent, two or more of these may be used. Among these, n-octyl mercaptan and t-dodecyl mercaptan are preferably used as the chain transfer agent.

(2-2) Separation Function Layer Formation Step The separation function layer formation step preferably includes the above step (c).
As an example of the step of forming the separation functional layer, an aqueous solution containing the above-mentioned polyfunctional amine (hereinafter, may be referred to as “polyfunctional amine aqueous solution”), water containing a polyfunctional acid halide, and non-polyfunctional acid halide. It is possible to form a polyamide skeleton by performing interfacial polycondensation on the surface of the porous support using an admixable organic solvent solution.

The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and preferably 15% by weight or less, more preferably 10% by weight. It is as follows. It is preferable that the concentration is in this range because sufficient water permeability and solute removal performance can be easily obtained.

Additives such as surfactants, alkaline compounds, acylation catalysts and antioxidants may be added to the polyfunctional amine aqueous solution as long as they do not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. Can be added.

Examples of the surfactant include sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium lauryl sulfate and the like.

Examples of the alkaline compound include sodium hydroxide, trisodium phosphate, triethylamine and the like.

In order to carry out interfacial polycondensation on the porous support, it is preferable that the above-mentioned polyfunctional amine aqueous solution is first brought into contact with the porous support. The contact is preferably carried out uniformly and continuously on the surface of the porous support.
Specific examples of the contact method include a method of coating a polyfunctional amine aqueous solution on a porous support and a method of immersing a support membrane in the polyfunctional amine aqueous solution.

The contact time between the porous support and the polyfunctional amine aqueous solution is preferably 1 second or longer, more preferably 3 seconds or longer, and preferably 10 minutes or shorter, more preferably 3 minutes or shorter.

After the polyfunctional amine aqueous solution is brought into contact with the porous support, it is preferable to sufficiently drain the liquid so that no droplets remain on the porous support. By sufficiently draining the liquid, it is possible to prevent the residual portion of the droplet from becoming a defect after the formation of the composite semipermeable membrane and deteriorating the removal performance of the composite semipermeable membrane.

As a method of draining the liquid, for example, a method of vertically grasping the support film after contact with the polyfunctional amine aqueous solution to allow the excess aqueous solution to flow down naturally, or a method of blowing an air flow such as nitrogen from an air nozzle to forcibly liquid the liquid. A cutting method or the like 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.

Next, water containing a polyfunctional acid halide and an immiscible organic solvent solution can be brought into contact with the porous support after contact with the polyfunctional amine aqueous solution to form a separation functional layer by intercondensation. preferable.

The concentration of the polyfunctional acid halide in the organic solvent solution immiscible with water is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and preferably 3% by weight or less. More preferably, it is 2% by weight or less. When the concentration of the polyfunctional acid halide is 0.01% by weight or more, a sufficient reaction rate can be easily obtained, and when it is 3% by weight or less, the occurrence of side reactions can be sufficiently suppressed.

The organic solvent immiscible with water is preferably one that 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. Examples of the organic solvent immiscible with water include hydrocarbon solvents, which may be simple substances or mixtures.
Examples of water-immiscible organic solvents are saturated hydrocarbons such as hexane, heptane, octane, nonane and decane; IP Solvent 1620, IP Clean LX IP Solvent 2028, Exxon Mobile's ISOPAR E, ISOPAR G, ISOPAR H , ISOPAR L and other isoparaffin solvents; examples thereof include naphthenic solvents such as Exol D30, Exol D40, Exol D60 and Exol D80 manufactured by Exxon Mobile.

The organic solvent solution immiscible with water may contain other polyfunctional amine-reactive monomers, other organic solvents, acylation catalysts, surfactants, solubilizers, complexing agents and the like. .. For example, other polyfunctional amine-reactive monomers include at least one selected from sulfonyl halides and acid anhydrides, preferably a compound containing 2-4 amine-reactive functional groups, at least one carboxy group. Examples include compounds containing at least one acyl halide. Examples of other organic solvents include benzene, toluene, acetone, ethyl acetate and the like. Examples of the acylation catalyst include DMF and the like.

Examples of the method of contacting the porous support with water containing a polyfunctional acid halide and an immiscible organic solvent solution include the same method as the method of coating the porous support with an aqueous solution of a polyfunctional amine. Be done.

In the interfacial polycondensation step, it is preferable that the porous support is sufficiently covered with a crosslinked polyamide thin film and the polyfunctional acid halide solution remains on the porous support. Therefore, the time for performing the interfacial polycondensation is preferably 0.1 seconds or more and 3 minutes or less, and more preferably 0.1 seconds or more and 1 minute or less. When the interfacial polycondensation is performed for 0.1 seconds or more and 3 minutes or less, it is easy to sufficiently cover the porous support with the crosslinked polyamide thin film, and the polyfunctional acid halide solution is applied on the porous support. Easy to hold.

After forming the separation functional layer on the porous support by interfacial polycondensation, it is preferable to drain the excess solvent. Examples of the method of draining the liquid include a method of grasping the membrane in the vertical direction and naturally flowing down the excess organic solvent to remove the liquid, a method of drying and removing the organic solvent by blowing air with a blower, and a mixing of water and air. A method of removing excess organic solvent with a fluid (two fluids) can be used.

Further, it is preferable to add a step of washing with pure water of 25 ° C. or higher and 90 ° C. or lower for 1 minute or longer.

3. 3. Utilization of Composite Semipermeable Membrane The composite semipermeable membrane of the present invention is preferably used as, for example, 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 above-mentioned composite semipermeable membrane, its elements, and modules can be combined with a pump for supplying raw water to them, a device for pretreating the raw water, and the like to form a fluid separation device. By using this separation device, it is possible to separate raw water into permeated water for drinking water and concentrated water that has not permeated the membrane, and obtain water suitable for the purpose.

The higher the operating pressure of the fluid separator, the better the salt removal property, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane of the present invention, the composite semipermeable membrane is covered. The operating pressure when permeating the treated water is preferably 0.2 MPa or more and 4.1 MPa or less, for example.
As the supply water temperature increases, the salt removability decreases, but as the temperature decreases, the membrane permeation flux also decreases. Therefore, for example, 5 ° C. or higher and 35 ° C. or lower are preferable.
In addition, if the pH of the supply water becomes high, scales such as magnesium may be generated in the case of supply water with a high salt concentration such as seawater, and there is a concern that the membrane may deteriorate due to high pH operation. Operation in the area is preferred.

Examples of the raw water treated by the composite semipermeable membrane include a liquid mixture containing 500 mg / L to 100 g / L of TDS (Total Dissolved Solids) such as seawater, brackish water, and wastewater. Generally, TDS refers to the total amount of dissolved solids and is represented by "mass / volume" or by "weight ratio" with 1 L as 1 kg. According to the definition, a solution filtered through a 0.45 μm filter is evaporated at a temperature of 39.5 to 40.5 ° C. and can be calculated from the weight of the residue, but more simply it is converted from the practical salt content.

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

<1. Measurement of cyano group ratio>
^{A composite semipermeable membrane (area 0.1 m 2} ) washed with pure water at 70 ° C. for 1 hour or more is air-dried at 25 ° C. and immersed in 200 mL of acetone at 25 ° C. for 20 hours to dissolve the porous support. A solution was obtained. Next, the obtained solution was filtered through a metal mesh (wire diameter 0.03 mm, 300 mesh, manufactured by Kansai Wire Mesh Co., Ltd.) to remove the base material and the separating functional layer. Subsequently, acetone was removed from the filtrate obtained using an evaporator to obtain an insoluble matter. The insoluble material was dried in a vacuum dryer at 25 ° C. for 5 hours, and then the insoluble material was dissolved again in acetone so as to be 10% by weight.
The obtained solution was applied onto a glass substrate to a thickness of 15 mil (381 μm) using an applicator, and left to stand in an atmosphere of a temperature of 25 ° C. and a humidity of 50% for 12 hours or more to obtain a film-like sample. The obtained sample was dried in a vacuum dryer at 60 ° C. for 5 hours to completely remove acetone, and the dried sample was subjected to absorbance analysis using a Fourier transform infrared spectrophotometer (FT-IR) (transmission method).
The cyano group ratio was determined from the formula (1) using the absorption intensity of the following peaks appearing in the obtained infrared absorption spectrum.
1605cm ^-1 : Peak attributed to vibration of benzene nucleus 2240cm ^-1 : Peak attributed to -CN expansion and contraction cyano group ratio = 2240cm ^-1 absorption intensity / 1605cm ^-1 absorption intensity (1)
FT-IR: IR Tracer-100 manufactured by Shimadzu Corporation
Measurement conditions: Apodizing function Happ-Genzel, resolution 4 cm ^-1 , number of scans 32, measurement range 600-4000 cm ^-1
Analytical conditions: After baseline correction with 3 points of 2200, 2600, 3800 cm ^-1 as zero absorption intensity, the absorption intensity of the peak was read.

<2. Measurement of composite semipermeable membrane thickness>
The composite semipermeable membrane washed with pure water at 70 ° C. for 5 minutes was air-dried at 25 ° C. The thickness of the dried sample was measured at any 20 points with a digital thickness gauge (SMD-565J-L manufactured by Teclock Co., Ltd.), and the arithmetic mean thereof was calculated as the composite semipermeable membrane thickness. As described above, since the thickness of the separation functional layer is very thin as compared with the base material and the porous support, the thickness of the composite semipermeable membrane is the total thickness of the base material and the porous support (thickness of the support film). ) Can be regarded as. The measured value of the composite semipermeable membrane thickness is shown as "support membrane thickness" in Table 1.

<3. Measurement of pure water permeability coefficient of support membrane>
The prepared support membrane was washed with pure water at 70 ° C. for 5 minutes. Next, it was cut out into a circle with a diameter of 4.3 cm, and the cut out sample was set in a stirring type ultra holder (UHP-43K manufactured by Advantech Toyo Co., Ltd.) (effective filtration area: 10.9 cm ² ). Subsequently, pure water at 25 ° C. was put into the cell, a cap was attached, and the pressure was increased to 100 kPa with nitrogen. Finally, the amount of pure water permeated over a certain period of time was measured, and the pure water permeation coefficient (× ^10-9 m ³ / m ² · s · Pa, 25 ° C.) was calculated from the following formula.
Pure water permeability coefficient = Pure water permeability ÷ (Membrane area x Water sampling time x Supply pressure)

<4. Measurement of weight average molecular weight Mw of THF-soluble matter in porous support>
^{A composite semipermeable membrane (area 0.1 m 2} ) washed with pure water at 70 ° C. for 1 hour or more is air-dried and immersed in THF (200 ml) at 25 ° C. for 4 hours to dissolve the porous support portion. A resin solution was obtained. A 250 ml container was used for immersion. Next, the obtained solution was filtered through a metal mesh (wire diameter 0.03 mm, 300 mesh, manufactured by Kansai Wire Mesh Co., Ltd.) to remove the base material and the functional layer. Subsequently, the obtained filtrate was subjected to a centrifuge (KUBOTA 6900) at 8800 r. p. After centrifuging at m (12,300 G) at 5 ° C. for 40 minutes, the supernatant was separated. The obtained supernatant was measured using GPC under the following conditions, and the weight average molecular weight (Mw) was calculated. Polystyrene was used as the calibration curve.
Solvent: Tetrahydrofuran Equipment: Waters 2695 Separation module Column: Tosoh Corporation TSKgel SuperIIZM-M, SuperIIZM-N, SuperHZ-L (3 in total)
Column temperature: 40 ° C
Solvent flow rate: 0.35 ml / min Detector: Waters 2414 differential refractive index detector

<5. Membrane performance evaluation>
The performance of the composite semipermeable membrane was evaluated by the method shown below.
(Salt removability (NaCl Rej.))
Raw water (NaCl concentration 500 ppm) prepared at a temperature of 25 ° C. and pH 7 is supplied to the composite semipermeable membrane at an operating pressure of 0.50 MPa to perform a membrane filtration treatment for 3 hours, and then the electrical conductivity of the supplied water and the permeated water is measured. It was measured with a multi-water quality meter (MM60R) manufactured by DKK-TOA CORPORATION. Next, using the calibration curve prepared in advance, this conductivity was converted to calculate the NaCl concentration. From this NaCl concentration, the salt removability, that is, the NaCl removal rate was determined by the following formula.
NaCl removal rate (%) = 100 × {1- (NaCl concentration in permeated water / NaCl concentration in feed water)}

(Membrane Permeation Flux (Flux))
In the test in the previous section, the amount of water permeated through the membrane was measured over a certain period of time, converted into the amount of water permeated per day (cubic meter) per square meter of membrane surface, and expressed as ^{the membrane permeation flux (m 3} / m ^{2 / day).} ..

The materials used in each example and comparative example are shown below.

(Production Example 1) Suspension polymerization medium (methyl methacrylate / acrylamide copolymer)
20 parts by weight of methyl methacrylate, 80 parts by weight of acrylamide, 0.3 part by weight of potassium persulfate and 1800 parts by weight of ion-exchanged water were charged into the reactor, and the gas phase in the reactor was replaced with nitrogen gas. The temperature was maintained at 70 ° C. with good stirring, and when the polymerization rate reached 99%, the polymerization was terminated to obtain an aqueous solution of a copolymer of methyl methacrylate and acrylamide. To this aqueous solution, 35 parts by weight of sodium hydroxide and 15,000 parts by weight of ion-exchanged water were added to obtain an aqueous solution of 0.6% by weight of a copolymer of methyl methacrylate and acrylamide. After stirring at 70 ° C. for 2 hours to saponify, the mixture was cooled to room temperature to obtain an aqueous solution of a medium for suspension polymerization.

(Production Example 2) Vinyl-based copolymer (A)
In a 20 L stainless steel autoclave, 6 parts by weight of the methyl methacrylate / acrylamide copolymer aqueous solution produced in Production Example 1 and 150 parts by weight of pure water were placed and stirred at 400 rpm, and the inside of the system was replaced with nitrogen gas. Next, a mixed solution of 72 parts by weight of styrene and 28 parts by weight of acrylonitrile, 0.40 parts by weight of t-dodecyl mercaptan, and 0.4 parts by weight of 2,2'-azobisisobutyronitrile was stirred. Was added to the system, and the temperature was raised to 60 ° C. to initiate polymerization. After the start of polymerization, the reaction temperature was raised to 65 ° C. over 30 minutes and then to 100 ° C. over 3 hours. Then, the inside of the system was cooled to room temperature, and the polymer was separated, washed and dried to obtain a vinyl copolymer A. The weight average molecular weight Mw of this vinyl-based copolymer A was 270,000.

(Production Example 3) Vinyl-based copolymer (B)
A vinyl-based copolymer B was obtained in the same manner as in Production Example 2 except that it was changed to 76 parts by weight of styrene, 24 parts by weight of acrylonitrile, and 0 parts by weight of t-dodecyl mercaptan. The weight average molecular weight Mw of this vinyl-based copolymer B was 340,000.

(Production Example 4) Vinyl-based copolymer (C)
A vinyl copolymer C was obtained in the same manner as in Production Example 3 except that the styrene was changed to 80 parts by weight and the acrylonitrile was changed to 20 parts by weight. The weight average molecular weight Mw of this vinyl-based copolymer C was 260,000.
(Production Example 5) Vinyl-based copolymer (D)
A vinyl copolymer D was obtained in the same manner as in Production Example 3 except that the styrene was changed to 82 parts by weight and the acrylonitrile was changed to 18 parts by weight. The weight average molecular weight Mw of this vinyl-based copolymer D was 280,000.
(Production Example 6) Vinyl-based copolymer (E)
A vinyl copolymer E was obtained in the same manner as in Production Example 3 except that the styrene was changed to 85 parts by weight and the acrylonitrile was changed to 15 parts by weight. The weight average molecular weight Mw of this vinyl-based copolymer E was 330,000.
(Production Example 7) Vinyl-based copolymer (F)
A vinyl copolymer F was obtained in the same manner as in Production Example 3 except that the styrene was changed to 90 parts by weight and the acrylonitrile was changed to 10 parts by weight. The weight average molecular weight Mw of this vinyl-based copolymer F was 310,000.

<Comparative example 1>
The vinyl-based copolymer A obtained in Production Example 2 was added to DMF so as to be 16% by weight, and the copolymer solution was prepared by heating and holding at 70 ° C. for 3 hours while stirring with a mechanical stirrer.
The prepared copolymer solution was cooled to 25 ° C. and filtered using a metal mesh (wire diameter 0.03 mm, 300 mesh, manufactured by Kansai Wire Mesh Co., Ltd.). Then, a resin solution (copolymer solution) was applied to a thickness of 120 μm on a non-woven fabric (thickness: about 90 μm, air permeability: 1.0 cc / cm ^{2 / sec) made of polyester fibers produced by the papermaking method.} Three seconds after the coating, the film was immersed in pure water at 20 ° C. for phase separation, and then washed with pure water at 70 ° C. for 5 minutes to obtain a support film.

The obtained support film was immersed in a 2.0 wt% aqueous solution of m-phenylenediamine (m-PDA) prepared with pure water for 10 seconds, and then slowly pulled up so that the film surface became vertical. After removing excess aqueous solution from the surface of the porous support by blowing nitrogen from the air nozzle, the support film is placed so that the film surface is horizontal, and a 25 ° C. n-decane solution containing 0.07% by weight of trimesic acid chloride is placed. Was applied so that the surface of the porous support was completely wet.
After allowing to stand for 30 seconds, the surface of the porous support was held vertically for 1 minute to drain the liquid in order to remove excess solution from the porous support, and the mixture was dried by blowing air at 25 ° C. using a blower. Then, it was washed with pure water at 70 degreeC for 5 minutes to obtain a composite semipermeable membrane. Table 1 shows the membrane performance of the obtained composite semipermeable membrane.

<Comparative Example 2, Examples 1 to 4>
In Comparative Example 1, B was used in Comparative Example 2, C was used in Example 1, D was used in Example 2, E was used in Example 3, and F was used in Example 4 instead of the vinyl copolymer A. The composite semipermeable membranes of Comparative Example 2 and Examples 1 to 4 were obtained in the same manner as in Comparative Example 1 except for the above. Table 1 shows the membrane performance of the obtained composite semipermeable membrane.
From Examples 1 to 4, a composite semipermeable membrane having high water permeability was obtained when the cyano group ratio of the porous support was 0.85 or less.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on March 25, 2020 (Japanese Patent Application No. 2020-053880), the contents of which are incorporated herein by reference.

The composite semipermeable membrane of the present invention can be particularly suitably used for desalination of brackish water and purification of tap water.

Claims

A composite semipermeable membrane comprising a base material, a porous support arranged on the base material, and a separation functional layer arranged on the porous support.
The porous support contains a copolymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer.
For the film obtained by dissolving and drying the porous support in a solvent, the following cyano group ratio represented by the absorption intensity of the infrared absorption spectrum measured by the Fourier transform infrared spectrophotometer is 0.20 or more and 0. A composite semipermeable membrane of .85 or less.
Cyan group ratio = 2240 cm -1 absorption intensity / 1605 cm -1 absorption intensity
The composite semipermeable membrane according to claim 1, wherein the cyano group ratio is 0.40 or more and 0.78 or less.
The composite semipermeable membrane according to claim 2, wherein the cyano group ratio is 0.40 or more and 0.62 or less.
The composite semipermeable membrane according to any one of claims 1 to 3, wherein the weight average molecular weight Mw of the copolymer is 220,000 or more and 1,000,000 or less.
The composite semipermeable membrane according to claim 4, wherein the weight average molecular weight Mw of the copolymer is 260,000 or more and 1,000,000 or less.