JP2855231B2 - Composite semipermeable membrane - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite semipermeable membrane, and more particularly, has a semipermeable ultrathin film on a porous substrate, and further has a quaternized polyvinylpyridine segment thereon. The present invention relates to a composite semipermeable membrane having excellent salt removing performance, which is obtained by laminating a membrane comprising a block copolymer or a graft copolymer having the following. .

2. Description of the Related Art In recent years, various types of composite semipermeable membranes in which a semipermeable ultrathin film is formed on a porous substrate as a reverse osmosis membrane are known as described later.

Composite semipermeable membranes with these ultrathin films are generally superior in reverse osmosis, such as salt removal performance and water permeability, to cellulose acetate membranes, which have been widely used as reverse osmosis membranes. However, it is still unsatisfactory in terms of salt removal rate for practical desalination. In particular, in the manufacture of semiconductors, ultrapure water used for cleaning LSIs has been required to be highly desalted pure water with the recent sophistication of LSI integration density.
Thus, a reverse osmosis membrane used in the production of ultrapure water is required to have a higher salt removal rate than before. Moreover, there is a strong demand for a treatment water containing a low concentration of salt, which has a higher salt removal rate.

DISCLOSURE OF THE INVENTION The present invention has been made in order to meet the above-mentioned demands, and is directed to a composite semipermeable membrane having excellent salt removal performance, particularly to treated water containing a low concentration of salt. It is an object of the present invention to provide a composite semipermeable membrane having a high salt removal rate.

Means for Solving the Problems The composite semipermeable membrane according to the present invention has a semipermeable ultrathin film on a porous substrate, and further has a block copolymer or graft having a quaternized polyvinylpyridine segment thereon. It is characterized in that thin films made of a copolymer are laminated.

In the present invention, the semipermeable ultrathin film is obtained by crosslinking a polyvalent amino compound having at least two primary and / or secondary amino groups in a molecule with a polyfunctional crosslinking agent capable of reacting with the amino group. It is a membrane. Such an ultrathin film is formed by applying an aqueous solution mainly containing a water-soluble polyvalent amino compound having at least two primary and / or secondary amino groups in a molecule on a porous substrate, and then applying the aqueous solution. A polyfunctional cross-linking agent capable of reacting with the amino group is brought into contact with the polyvalent amino compound to form a polymer by interfacial polymerization and crosslinking, and usually has a thickness of 50 to 10,000, preferably 100 to 5000, Having.

Here, the water-soluble polyvalent amino compound having at least two primary and / or secondary amino groups in the molecule has a molecular weight of
Including high molecular weight polymers from monomer compounds in the range of 50 to 500,000, specifically, for example, polyethyleneimine, amine-modified polyepichlorohydrin, water-soluble oligomers by polymerization of epoxy compounds and amino compounds, and the like Polymer,
Examples include phenylenediamine, diaminopyridine, diaminodiphenyl ether, diaminodiphenylsulfone, piperazine, 2,5-dimethylpiperazine, homopiperazine, ethylenediamine and the like.

Further, as the polyfunctional crosslinking agent, a compound having at least two functional groups capable of reacting with the amino group of the water-soluble amino compound such as an isocyanate group, an acid halide group, and an N-haloformyl group in a molecule is preferable. Used, specifically, isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, tolylene diisocyanate, 4,
4'-diphenyl ether diisocyanate, 4,4'-diphenyl methane diisocyanate and the like can be mentioned.

The semipermeable ultra-thin film using the polyvalent amino compound and the polyfunctional crosslinking agent as described above is usually prepared by applying an aqueous solution of the water-soluble polyvalent amino compound on a porous substrate, and then applying the polyfunctional crosslinking agent , To cause interfacial polymerization, followed by heat curing to obtain a dry film.
The porous substrate is not particularly limited, but includes, for example, a polysulfone membrane, a polyethersulfone membrane, a polyacrylonitrile membrane, a cellulose ester membrane,
A polyvinyl chloride film or the like can be suitably used.

As described above, various types of composite semipermeable membranes formed by forming a semipermeable ultrathin film on a porous substrate are already known,
For example, a composite semipermeable membrane having an ultrathin film obtained by crosslinking polyethyleneimine with tolylene diisocyanate on a polysulfone porous substrate (JP-A-49-133282), an amine-modified polyepichlorohydride instead of polyethyleneimine Composite semipermeable membrane formed by crosslinking phosphorus with a polyfunctional crosslinking agent similar to the above to form an ultrathin film (Japanese Patent Publication No. 55-38164), a water-soluble oligomer obtained by polymerization of an epoxy compound and an amino compound Is cross-linked with the same cross-linking agent as above to form an ultrathin film (JP-A-53-144844), a water-soluble polymer such as polyethyleneimine, and two or more amino groups in the molecule. A composite semipermeable membrane in which an ultrathin film is formed by co-crosslinking a polyvalent amino compound monomer with the same polyfunctional crosslinking agent as described above (JP-A-56-139105) can be exemplified.

In addition to the above, a composite semipermeable membrane formed by crosslinking an aromatic monomer having at least two primary amino groups in a molecule with a polyfunctional acyl halide-substituted aromatic monomer to form an ultrathin film (in particular, Japanese Patent Laid-Open No. 55-147106), a composite semipermeable membrane in which polyvinyl alcohol and an amino compound having two or more secondary amino groups in a molecule are cross-linked with a polyfunctional cross-linking agent to form an ultra-thin film (Japanese Patent Publication No. 61-147106). 27083) and the like.

The composite semipermeable membrane according to the present invention further comprises a block copolymer or graft copolymer having a quaternized polyvinylpyridine segment on the semipermeable ultrathin film of such a conventional composite semipermeable membrane. Thin films are stacked.

As the block copolymer, those comprising a quaternized polyvinylpyridine segment A and a monovinyl aromatic polymer segment B having a glass transition point of 50 ° C. or higher are preferably used. Such a copolymer may be any one of a diblock represented by AB, a triblock represented by BAB, or a mixture thereof.

In the block copolymer, the molecular weight of the quaternized polyvinyl pyridine segment is appropriately from 1,000 to 200,000, preferably from 1,000 to 100,000, as the polyvinyl pyridine segment before quaternization. Polyvinylpyridine segment before quaternization has a molecular weight of 200,000
If it exceeds, the solubility in a solvent is lowered, which is not preferred.

Further, in the block copolymer, the content of the polyvinyl pyridine component before quaternization is preferably in the range of 10 to 90 mol%.

As the monovinyl aromatic polymer segment B, for example, a block formed by polymerizing a styrene monomer such as styrene, α-methylstyrene, vinyl toluene, and vinyl xylene is preferable, and a block formed of polystyrene is particularly preferable. preferable. Its molecular weight is 3000-10
A range of 0000 is appropriate.

Next, the graft copolymer is preferably composed of a quaternized polyvinylpyridine A and a water-insoluble polymer C. In this case, either one may be a trunk component or a branch component.

The water-insoluble polymer C preferably comprises a homopolymer or a copolymer of at least one radical polymerizable monomer selected from a vinyl monomer and an acrylic monomer.

Examples of the vinyl monomer include styrene, α
Styrene monomers such as methylstyrene, vinyl acetate,
Examples thereof include vinyl esters such as vinyl propionate, and vinyl chloride. Examples of the acrylic monomer include, for example, methyl acrylate, ethyl acrylate, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, t-butyl phenyl methacrylate, naphthyl acrylate, -Cyanophenyl acrylate, acrylamide, acrylonitrile, methacrylonitrile and the like. These may be used alone depending on the monomer, or in combination with another monomer depending on the monomer.

The molecular weight of the branch component in the graft copolymer is 500 to 100,000, preferably 1000 when the component A is a branch component.
~ 50000, and when the C component is a branch component, 5
The range is from 100 to 100,000, preferably from 1,000 to 50,000. When the molecular weight of the branch component exceeds 100,000, the concentration of the terminal functional group decreases during polymerization, the polymerization reactivity is impaired, and it becomes difficult to obtain the intended graft copolymer. On the other hand,
When the molecular weight of the branch component is smaller than 1,000, it is difficult to achieve the intended effect of the present invention.

In the graft copolymer, the water-insoluble polymer is
Polystyrene is preferred, and the polyvinyl pyridine component before quaternization preferably accounts for 10 to 90 mol%.

In the present invention, the above block copolymer and graft copolymer can be obtained, for example, by the following method.

First, with regard to the block copolymer, those obtained by anionic polymerization as described in JP-B-56-39648 are preferable because the size and arrangement of the segments are extremely constant. Regarding the graft copolymer, first, a macromonomer of the component A or the component B is prepared by a known living anionic polymerization, and then the copolymer is co-polymerized with the component B or the component A by a radical polymerization. It can be obtained by polymerizing.

As such a quaternizing agent for the block copolymer and the graft copolymer, an alkyl halide having 1 to 20 carbon atoms and an alkyl dihalide having 1 to 18 carbon atoms are preferable. Particularly, from the viewpoint of reactivity, bromide is preferable. Or iodide is preferred. Accordingly, for example, alkyl halides such as methyl bromide, ethyl bromide, n-octyl bromide and methyl iodide, ethyl dibromide, n-nonyl dibromide, lauryl dibromide and the like are preferably used.

In the present invention, the quaternization ratio of the block copolymer and the graft copolymer is preferably 10% or more. When the quaternization ratio is less than 10%, the resulting composite semipermeable membrane is inferior in water permeability, and the effect of removing salts is not recognized, which is not preferable.

In the present invention, the method for quaternizing the block copolymer and the graft copolymer using the quaternizing agent includes dissolving the copolymer and the quaternizing agent in an appropriate solvent, and dissolving this solution on a water surface described later. A method in which the film is thinned by a developing method and closely laminated on the composite semipermeable membrane and then subjected to a heat treatment is preferable, but other methods can also be used.

As such a quaternization method, first, a method in which the copolymer and the quaternizing agent are dissolved in a solvent and then heated and stirred, and in this case, the solvent used is a side reaction. Those which do not cause or hinder the reaction and which dissolve the raw materials and products are preferable. Therefore, for example, alcohols such as methanol and ethanol, dimethylformamide, dimethylacetamide, N
Polar solvents such as -methylpyrrolidone are preferred. As a second method, there is a method in which a thin film made of the copolymer is formed on the composite semipermeable membrane by an appropriate method, and then reacted with the quaternizing agent under reduced pressure.

In order to coat the thin film of the copolymer on the semipermeable ultrathin film, a method of melt-coating the copolymer, a method of dissolving the copolymer in an appropriate organic solvent, and a method of applying and drying this solution In particular, the water surface spreading method described below is applied to a case where the porous base material of the composite semipermeable membrane has poor heat resistance or poor solvent resistance. Can also be employed, and it is preferably employed because a copolymer thin film having a uniform film thickness can be obtained.

In the water surface development method, for example, as shown in FIG. 1, a solution of the copolymer is discharged from a nozzle 1 onto a water surface 3 in a water tank 2 by a metering pump (not shown), and the aqueous solution is spontaneously generated. To form a copolymer thin film 4. The thin film thus obtained is brought into contact with the traveling composite semipermeable membrane 8 by rolls 5, 6 and 7 to be closely laminated.

As the developing solvent used in such a water surface developing method, an inert solvent that dissolves the copolymer is preferable, for example,
Alcohols such as methanol and ethanol, polar solvents such as tetrahydrofuran, dimethylformamide and dimethylacetamide, water or a mixed solvent thereof are used. In particular, when sufficient water surface developability cannot be obtained even when a single solvent is used, the first auxiliary is used as a development aid.
It is effective to add a second organic solvent to the developing solvent. Examples of such development aids include aliphatic and aromatic ketones, esters, alcohols, amines, aldehydes, peroxides, and mixtures thereof.

The concentration of the copolymer solution used in the water surface spreading method is 0.5 to 5
0% by weight, preferably in the range of 1 to 40% by weight. When the copolymer concentration is too low, a uniform and continuous thin film cannot be obtained.On the other hand, when the copolymer concentration is too high,
This is not preferable because the spreadability of the solution on the water surface is reduced.

When laminating a thin film of the block copolymer or the graft copolymer on the composite semipermeable membrane, the thin film may be laminated in a single layer, or may be laminated in two or more layers. . When laminating into multiple layers, it is preferable to sufficiently dry the moisture adhering to the previously laminated thin film before laminating.

In the composite semipermeable membrane according to the present invention, the thickness of the membrane made of such a graft copolymer is usually 30 ° to 10 μm.
Range is good. When the thickness of the graft copolymer is less than 30 °, the salt removal performance is not improved, while
If it exceeds μm, the water permeability of the membrane is unpreferably reduced.

Effect of the Invention As described above, the composite semipermeable membrane according to the present invention has a thin film made of a block copolymer or a graft copolymer having a quaternized polyvinylpyridine segment on a semipermeable ultrathin film. In addition, the chargeability of the quaternized polyvinyl pyridine segment impedes the permeation of ions such as sodium chloride, but does not impede the water permeability of the underlying composite semipermeable membrane. It has a high salt removal rate with respect to the treated water contained.

EXAMPLES Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Reference Example 1 0.1 mol /
Was charged with 6.5 g of a cyclohexane solution of sec-butyllithium and 15 g of styrene, and the mixture was stirred for 30 minutes while cooling the reactor on an ice-water bath to obtain a living polymer of styrene.

Next, 25 g of purified 2-vinylpyridine was added to the reactor, and the mixture was further stirred on an ice water bath for 30 minutes.
A poly (2-vinylpyridine) living polymer was obtained.

The diblock copolymer was taken out of the reactor, purified, and analyzed by GPC and proton NMR. As a result, the polystyrene block had a number average molecular weight of
2300, polyvinyl pyridine block has a number average molecular weight of 3700
It had 0.

Reference Example 2 In the same manner as in Reference Example 1, first, a polystyrene-poly (2-vinylpyridine) living diblock copolymer was obtained, and then, 3.25 mmol of 1,4-dibromobutane was added to this solution.
l, add polystyrene-poly (2-vinylpyridine)
-A triblock copolymer consisting of polystyrene was obtained.
As a result of GPC analysis, this block copolymer had a triblock ratio of 84%.

10 g of this triblock copolymer was dissolved in 50 ml of dimethylformamide, and 10 g of ethyl bromide was added.
The mixture was stirred at reflux at a temperature of 8 ° C. for 8 hours to cause a quaternization reaction.
Then, dimethylformamide and excess ethyl bromide were removed under reduced pressure to obtain a polystyrene-quaternized polyvinylpyridine-polystyrene triblock copolymer.

Reference Example 3 0.1mol /
Was charged with 24 ml of a cyclohexane solution of sec-butyllithium and 15 g of styrene, and the mixture was stirred for 30 minutes while cooling the reactor on an ice water bath to obtain a living polymer of styrene.

Next, 2 g of ethylene oxide was added to the reactor,
Further, 3 g of methacrylic acid chloride was added and stirred for 30 minutes to obtain a polystyrene macromonomer.

After purifying this macromonomer, GPC and proton N
As a result of analysis by MR, the number average molecular weight was 6500,
The terminal functional group modification rate was 98%.

10 g of this polystyrene macromonomer and 10 g of 2-vinylpyridine were dissolved in 30 ml of benzene, and 0.1 g of azobisisobutyronitrile was further added. Was styrene and the trunk portion was vinylpyridine.

As a result of analyzing the obtained graft copolymer by GPC and proton NMR, the number average molecular weight was 30,000, the weight average molecular weight was 85,000, and the ratio of the poly-2-vinylpyridine component was 45%. .

Reference Example 4 0.1 mol /
Was charged with 25 ml of a cyclohexane solution of sec-butyllithium and 13 g of purified 2-vinylpyridine, and stirred for 30 minutes while cooling the reactor on an ice-water bath to obtain a living polymer of 2-vinylpyridine.

Next, p-vinylbenzyl chloride was added to the reactor.
2 g was added and stirred for 30 minutes to obtain a poly (2-vinylpyridine) macromonomer.

After purifying this macromonomer, GPC and proton N
As a result of analysis by MR, the number average molecular weight was 5500,
The terminal functional group modification rate was 96%.

10 g of this poly (2-vinylpyridine) macromonomer
And styrene (10 g) dissolved in benzene (30 ml) .Additionally, azobisisobutyronitrile (0.1 g) was added thereto, and the mixture was stirred under a nitrogen atmosphere at 60 ° C. for 24 hours. Was obtained.

As a result of analyzing the obtained graft copolymer by GPC and proton NMR, the number average molecular weight was 40,000, the weight average molecular weight was 150,000, and the ratio of the poly-2-vinylpyridine component was 48%. .

Comparative Example 1 A composite semipermeable membrane was prepared according to the method described in JP-A-55-147106.

Example 1 The block copolymer prepared in Reference Example 1 and n-lauryl dibromide in an amount equivalent to the vinylpyridine component thereof were dissolved in a mixed solvent of an equivalent amount of tetrahydrofuran / water. A thin film having a thickness of 0.05 μm was developed by a water surface spreading method as shown in the figure and laminated on the composite semipermeable membrane shown as the comparative example to obtain a composite semipermeable membrane according to the present invention.

The copolymer concentration of the block copolymer solution was 10% by weight, the supply amount of the copolymer solution to the water surface was 0.07 ml / min, and the film formation rate was 7%.
m / min.

Thereafter, the composite semipermeable membrane was heated at 110 ° C. for 40 minutes to quaternize and crosslink the block copolymer.

Example 2 The block copolymer prepared in Reference Example 2 was dissolved in a mixed solvent of equivalent amounts of tetrahydrofuran / water, and this solution was developed into a thin film having a thickness of 0.05 μm by a water surface spreading method in the same manner as described above. Laminated on the composite semipermeable membrane shown as a comparative example,
A composite semipermeable membrane according to the present invention was obtained.

The copolymer concentration of the block copolymer solution was 10% by weight, the supply amount of the copolymer solution to the water surface was 0.07 ml / min, and the film formation rate was 7%.
m / min.

Example 3 The graft copolymer prepared in Reference Example 3 and n-lauryl dibromide in an equivalent amount to the vinylpyridine component were dissolved in a mixed solvent of an equivalent amount of tetrahydrofuran / water. Similarly, it was developed into a thin film having a thickness of 0.05 μm by a water surface spreading method and laminated on the composite semipermeable membrane shown as the comparative example to obtain a composite semipermeable membrane according to the present invention.

The copolymer concentration of the graft copolymer solution was 10% by weight, the supply amount of the copolymer solution to the water surface was 0.07 ml / min, and the film formation speed was 7%.
m / min.

Thereafter, the composite semipermeable membrane was heated at 110 ° C. for 40 minutes to quaternize and crosslink the graft copolymer.

Example 4 The graft copolymer prepared in Reference Example 4 and an equal amount of n-lauryl dibromide with respect to the vinylpyridine component were dissolved in a mixed solvent of tetrahydrofuran / water in the same amount, and this solution was treated as described above. Similarly, it was developed into a thin film having a thickness of 0.05 μm by a water surface spreading method and laminated on the composite semipermeable membrane shown as the comparative example to obtain a composite semipermeable membrane according to the present invention.

The copolymer concentration of the graft copolymer solution was 10% by weight, the supply amount of the copolymer solution to the water surface was 0.07 ml / min, and the film formation speed was 7%.
m / min.

Thereafter, the composite semipermeable membrane was heated at 110 ° C. for 40 minutes to quaternize and crosslink the graft copolymer.

For each composite semipermeable membrane obtained as described above, a 1 ppm aqueous solution of an aqueous sodium chloride solution was brought into contact with the composite semipermeable membrane under the conditions of pH 6 to 7, a temperature of 25 ° C., and a pressure of 15 kg / cm ² as treated water. The reverse osmosis test was performed by measuring the ion permeability. The results are shown in Table 1. Where the ion permeability is Is defined by

In addition, the concentration values of sodium ion and chloride ion were determined based on respective calibration curves prepared in advance by ion chromatography analysis.

As is clear from the results shown in Table 1, Examples 1 to 4
The composite semipermeable membrane according to Comparative Example 2 has a lower ion permeability without impairing the water permeability as compared with the composite semipermeable membrane according to Comparative Example, and thus has an improved salt removal rate.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method of laminating a thin film on a composite semipermeable membrane by a water surface spreading method. 1 ... Nozzle, 2 ... Water tank, 3 ... Water surface, 4 ... Copolymer thin film, 8 ... Composite semi-permeable membrane.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshihiro Minamizaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (56) References JP-A-4-7026 (JP, A) (58) ) Field surveyed (Int.Cl. ⁶ , DB name) B01D 71/78 B01D 71/80 B01D 71/28 B01D 69/12

Claims (1)

(57) [Claims] 1. A block copolymer having a semipermeable ultra-thin film on a porous substrate, and further having a segment or branch made of a water-insoluble polymer and a quaternized polyvinylpyridine segment. A composite semipermeable membrane, wherein thin films comprising a graft copolymer are laminated.