JP3092864B2 - Separation membrane and separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation membrane and a separation method for a liquid-liquid mixture, a liquid-gas mixture, and a gas-gas mixture, and more particularly to a liquid (or vapor) having high solubility with an acrylic copolymer.
And a separation method using the separation membrane, which can be suitably used to separate from the acrylic copolymer and a liquid (or vapor) having low solubility.

[0002]

2. Description of the Related Art A membrane separation method for separating various mixtures using a membrane having pores is disclosed in US Pat.
In recent years, it has become increasingly popular, and its technology is being applied in various fields. The object to be separated in the membrane separation method is also a solid-
There is an interest in the development of separation membranes and separation techniques for a wide variety of mixtures, not only liquid mixtures, but also liquid-liquid, gas-gas and gas-liquid mixtures.

[0003] Separation of organic solvents and the like by a membrane separation method is also one of the fields of interest, and is a mixture which cannot be separated by a conventional simple method (for example, a mixture having a boiling point close to and difficult to separate by distillation). , Azeotropes, mixtures containing heat-sensitive substances, etc.). The pervaporation method, the reverse osmosis method, and the evaporation method (vapor permeation method) are suitable for the membrane separation method of the mixture of the organic solvents.

[0004] Incidentally, the accuracy and efficiency of the separation in the membrane separation method including the pervaporation method, the reverse osmosis method and the evaporation method depend on the performance of the membrane itself.
It is important to develop a membrane with excellent separation selectivity.

In order to obtain an excellent separation membrane, basically, it is necessary to selectively increase the affinity with the compound to be separated. However, if the entire separation membrane is made of a material having an affinity for the target component, the separation membrane swells, and high separation selectivity cannot be obtained due to the plasticizing effect. In addition, there is a problem that the mechanical strength and durability of the separation membrane are reduced.

Accordingly, a separation membrane comprising a composite membrane having a structure in which the pores of the membrane are substantially filled with a polymer using a microporous membrane made of a material that does not swell in an organic solvent has been developed. I have. Here, the polymer that fills the pores has a good affinity for the object to be separated, and suppresses swelling of the entire membrane while separating only specific components through the pores filled with the polymer.

As a separation membrane of this type, the present applicant has previously described
A patent application was filed for a separation membrane in which an acrylic monomer was plasma-polymerized on a polyethylene microporous membrane and the pores were substantially filled with an acrylic graft polymer (Japanese Patent Application No. 1-2344).
No. 88). This separation membrane can satisfactorily separate benzene from a benzene / cyclohexane mixture, for example, with high selectivity.

However, in the above-mentioned separation membrane, since the one that fills the pores is a graft polymer of a single monomer, there is a limit in the combination of liquids that can be separated, and liquids having similar solubility with the graft polymer are limited. It is difficult to perform good separation on the mixture of Accordingly, there has been a demand for the development of a separation membrane whose solubility can be controlled so that it can be widely used for separating various liquid mixtures.

Accordingly, it is an object of the present invention to provide a separation membrane capable of performing separation with high selectivity on various liquid or vapor mixtures. Another object of the present invention is to provide a method capable of separating a target liquid or vapor with high selectivity for various liquid or vapor mixtures.

[0010]

Means for Solving the Problems As a result of intensive studies in view of the above object, the present inventor has used a microporous polyethylene membrane,
By performing plasma graft polymerization using multiple types of monomers with different solubility on the surface of this membrane, a separation membrane whose pores are substantially filled with the graft copolymer should be separated, and the compounding ratio of the monomer should be separated The present inventors have found that an organic solvent having solubility in a graft copolymer can be selectively permeated and separated if adjusted according to the type of liquid, and the present invention has been completed.

That is, the separation membrane of the present invention which can selectively separate a desired mixed liquid or vapor is obtained by performing plasma graft polymerization on a polyethylene microporous membrane using a plurality of types of monomers having different solubilities. The pores of the microporous membrane are substantially filled with the produced graft copolymer, and the compounding ratio of the monomer is such that the liquid or vapor to be separated in the mixed liquid is mixed with the produced graft copolymer. On the other hand, it is characterized in that it is selected so that it becomes a good solvent and the others become poor solvents.

Further, the method of the present invention for selectively separating a specific liquid or vapor from a mixed liquid or vapor by a pervaporation method, a reverse osmosis method or an evaporation method, comprises dissolving a specific liquid or vapor in a polyethylene microporous membrane. A separation membrane in which pores of the microporous membrane are substantially filled with a graft copolymer by performing plasma graft polymerization using a plurality of types of monomers having different properties, and at that time, the mixing ratio of the monomer Is selected so that a specific liquid or vapor in the mixed liquid or vapor becomes a good solvent for the produced graft copolymer, and the others become poor solvents.

Hereinafter, the present invention will be described in detail. First, the mixed liquid or vapor separation membrane (hereinafter, referred to as a separation membrane for simplicity) of the present invention will be described.

The separation membrane of the present invention is based on a microporous polyethylene membrane. As the polyethylene microporous membrane, those made of ultrahigh molecular weight polyethylene and high density polyethylene can be used, but those made of ultrahigh molecular weight polyethylene are preferably used from the viewpoint of strength.

The porosity of the microporous polyethylene membrane is preferably in the range of 30 to 95%, more preferably 50 to 90%. If the porosity is less than 30%, the permeability of the object to be separated becomes insufficient, while if it exceeds 95%, the mechanical strength of the membrane becomes small and the practicability is poor.

The average pore size is preferably in the range of 0.005 to 1 μm. When the average pore size is less than 0.005 μm,
If the target substance for separation becomes insufficient in permeability, and if the average pore size exceeds 1 μm, the separation performance is reduced.

Further, the breaking strength is preferably 200 kg / cm ² or more. By setting the breaking strength to 200 kg / cm ² or more, deformation resistance against swelling when the solvent is dissolved in the acrylic graft copolymer becomes sufficient.

The thickness of the microporous polyethylene membrane is preferably 0.1 to 50 μm, more preferably 0.2 to 25 μm. If the thickness is less than 0.1 μm, the mechanical strength of the film is small,
Difficult to put into practical use. On the other hand, if it exceeds 50 μm, the thickness is too large and the transmission performance is reduced, which is not preferable.

Ultra-high molecular weight polyethylene is a crystalline linear ultra-high molecular weight polyethylene comprising a homopolymer of ethylene or a copolymer of ethylene and 10 mol% or less of α-olefin. 5 × 10 molecular weight
^{It is 5} or more, preferably 1 × 10 ⁶ to 1 × 10 ⁷ . The weight average molecular weight of the ultra high molecular weight polyethylene affects the mechanical strength of the obtained separation membrane. If the weight average molecular weight is less than 5 × 10 ⁵ , a very thin and high strength separation membrane cannot be obtained. On the other hand, the upper limit of the weight average molecular weight is not particularly limited. However, if the weight average molecular weight exceeds 1 × 10 ⁷ , it is not preferable because it is difficult to form a thin film by stretching.

In the case of a microporous ultrahigh molecular weight polyethylene membrane,
A material obtained by blending another relatively low molecular weight polyethylene with the ultrahigh molecular weight polyethylene can be used. In this case, a polyethylene composition containing 1% by weight or more of an ultrahigh molecular weight polyethylene having a weight average molecular weight of 7 × 10 ⁵ or more and a weight average molecular weight / number average molecular weight of 10 to 300 is preferable.

The weight average molecular weight / number average molecular weight of the polyethylene composition is from 10 to 300, preferably from 12 to 250. When the weight-average molecular weight / number-average molecular weight is less than 10, the average molecular chain length is large and the entanglement density of the molecular chains upon dissolution becomes high, so that it is difficult to prepare a high-concentration solution. Also
If it exceeds 300, low molecular weight components are broken at the time of stretching, and the strength of the whole film decreases.

The weight-average molecular weight / number-average molecular weight is:
It is used as a measure of the molecular weight distribution, and the width of the molecular weight distribution increases as the ratio of the molecular weights increases.
That is, in a composition composed of polyethylene having different weight average molecular weights, as the ratio of the molecular weights of the composition is larger,
The difference in weight average molecular weight of polyethylene to be compounded is large,
The smaller the weight average molecular weight, the smaller the difference.

The content of the ultrahigh molecular weight polyethylene in the polyethylene composition is 1% by weight or more, based on 100% by weight of the whole polyethylene composition. When the content of the ultrahigh molecular weight polyethylene is less than 1% by weight, the entanglement of the molecular chain of the ultrahigh molecular weight polyethylene which contributes to the improvement of the stretchability is hardly formed, and a high strength microporous membrane cannot be obtained. On the other hand, the upper limit is not particularly limited, but if it exceeds 90% by weight, it will be difficult to achieve the desired high concentration of the polyethylene solution.

The polyethylene other than the ultrahigh molecular weight polyethylene in the polyethylene composition has a weight average molecular weight of:
It is less than 7 × 10 ⁵ , but the lower limit of the molecular weight is 1
× 10 ⁴ or more is preferred. Weight average molecular weight is 1 × 10
^Use of a polyethylene having a molecular weight of less than ⁴ is not preferred because breakage easily occurs during stretching and a desired microporous film cannot be obtained. In particular, it is preferable to blend a polyethylene having a weight average molecular weight of 1 × 10 ⁵ or more and less than 7 × 10 ⁵ with the ultrahigh molecular weight polyethylene.

Examples of such polyethylene include those of the same type as the ultrahigh molecular weight polyethylene described above.
Particularly, high-density polyethylene is preferable.

The above-mentioned microporous polyethylene membrane may contain an antioxidant, an ultraviolet absorber, a lubricant,
Various additives such as an anti-blocking agent, a pigment, a dye, and an inorganic filler can be added as long as the object of the present invention is not impaired.

Here, a method for producing a microporous ultrahigh molecular weight polyethylene membrane will be described. First, in the case of a microporous membrane consisting of ultra-high molecular weight polyethylene alone, for example, see JP-A-60-2
It can be produced by the method described in 42035.

Next, in the case of a microporous membrane made of a polyethylene composition obtained by blending ultra-high molecular weight polyethylene with relatively low molecular weight polyethylene, it can be produced by the following method.

First, a high concentration solution is prepared by heating and dissolving the above polyethylene composition in a solvent. The solvent is not particularly limited as long as it can sufficiently dissolve the polyethylene composition, and may be the same as that described in JP-A-60-242035. The heating dissolution is carried out with stirring at a temperature at which the polyethylene composition completely dissolves in the solvent. The temperature varies depending on the polymer and solvent used, but is preferably in the range of 140 to 250 ° C. Further, the concentration of the polyethylene composition solution is 10 to 50% by weight, preferably 10 to 50% by weight.
40% by weight.

Next, the heated solution of the polyethylene composition is extruded from a die and molded. As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical hollow die, an inflation die and the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm.
Heated to ~ 250 ° C. At this time, the extrusion speed is usually 20
3030 cm / min to 2-3 m / min.

The solution thus extruded from the die is formed into a gel by cooling. Cooling is preferably performed at a rate of 50 ° C./min or more at least up to the gelation temperature.

Next, this gel-like molded product is stretched. The stretching is performed by heating the gel-like molded product and at a predetermined magnification by a usual tenter method, a roll method, an inflation method, a rolling method or a combination of these methods, as described above. 2
Axial stretching is preferred, and either longitudinal or transverse simultaneous stretching or sequential stretching may be used, but simultaneous biaxial stretching is particularly preferred.

The stretching temperature is the melting point of the polyethylene composition +
It is 10 ° C. or less, preferably in the range from the crystal dispersion temperature to less than the crystal melting point. For example, 90 to 140 ° C., more preferably 100
In the range of ~ 130 ° C.

In the separation membrane of the present invention, a graft copolymer comprising a plurality of monomers is formed on at least the inner surface of the pores of the above-mentioned microporous polyethylene membrane, and the graft copolymer is substantially fine. It has a structure filled with holes. The graft polymerization of the monomer is performed by a plasma graft polymerization method as described later.

In order to form a graft copolymer, a plurality of types of monomers having different solubilities (different in solubility parameter or χ parameter to be described later) with respect to each liquid component in the mixed liquid are used. Two types of monomers may be used.

As the monomers, acrylic acid, methyl glycidyl acrylate, ethyl acrylate,
Butyl acrylate, methyl methacrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-
Examples thereof include vinylpyridine, styrene, acrylonitrile, acrylamide, and the like, and two or more of them can be used. Alternatively, the above monomers and acrylamine, allyl alcohol, diallylamine, diallyl maleate, allyl glycidyl ether, vinyl acetate, N-vinyl-2-pyrrolidone,
Ethyl vinyl ether, methyl vinyl ketone, divinylbenzene, 2-hydroxyethyl acrylate, ethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, maleic anhydride, and the like can be used in combination.

When two kinds of acrylic monomers are selected from the above-mentioned monomers and used, (a) a monomer species composed of acrylic acid, methacrylic acid or esters thereof, and (b) a monomer species composed of acrylamide or a derivative thereof Can be used. In this case, (a) the monomer has high solubility such as acetone and benzene, and (b) the monomer has high solubility such as water. In particular, an acrylate ester, more preferably methyl acrylate, is used as the (a) species, and acrylamide is used as the (b) species.

The above-mentioned two types of acrylic monomers (a) and (b) may be used in appropriate amounts (ratio of the (a) type and (b) type monomers in the graft copolymer) depending on the substance to be separated. select. Specifically, it is preferable to determine the mixing ratio of the (a) species and the (b) species in consideration of the Hansen parameter, which is one of the solubility parameters representing the solubility described below.

The solubility can be represented by a solubility parameter or a χ parameter. A parameter expressed three-dimensionally by dividing the solubility parameter into three components, an effect δ _d due to nonpolar interaction, an effect δ _p due to a polarization force, and an effect δ _h due to a hydrogen bond, is called a Hansen parameter. The χ parameter is an interaction parameter between the polymer and the solvent, and is given as the sum of the interaction entropy effect and the mixing heat effect.

As for the Hansen parameter, its value has been examined for many solvents (CM Hansen, e).
t al., "Encyclopedia of Chemical Technology", NY,
p.889,1971). When the Hansen parameters of a solvent (good solvent) and a poor solvent that are highly soluble in a specific polymer are plotted on three-dimensional spatial coordinates formed by δ _d , δ _p , and δ _h , the Hansen parameter of a good solvent ( δ _d ,
It can be seen empirically that δ _p , δ _h ) is located within a sphere of a certain size. Here, when a certain polymer 1 and a solvent 2 are considered, a distance r between the two on a three-dimensional space coordinate is a square root of Δ obtained by the following equation. Δ = (δ _d2 −δ _d1 ) ² + (δ _p2 −δ _p1 ) ² + (δ _h2 −δ _h1 ) ² (where δ _d1 , δ _p1 , δ _h1 are the Hansen parameters of polymer 1, δ _d2 , δ _p2 and _δh2 are Hansen parameters of the solvent 2). The Hansen parameters of the polymer 1 are empirically determined as described above. If this distance r is smaller than a certain value, it can be regarded as a good solvent for this polymer. Therefore, when the Hansen parameters of various solvents are plotted for a specific polymer, and a distinction is made between a good solvent and a poor solvent, it can be seen that the region surrounded by the good solvent is substantially spherical. In other words, this virtual sphere (center (δ _d1 ,
Solvents whose Hansen parameters fall within the radius r) at δ _p1 , δ _h1 ) have high solubility for polymers, and solvents with Hansen parameters outside the sphere have good solubility for polymers. Will not be shown. In order to distinguish a good solvent from a poor solvent, a value S (a ratio of a liquid (solvent) volume to a unit volume of a film when swollen) obtained by a sorption test can be used.

When a plurality of types of monomers having different Hansen parameters are combined and copolymerized, the Hansen parameters of the obtained copolymer change according to the proportion of the blended monomers. In the present invention, the blending amounts of the plurality of monomers forming the graft copolymer are adjusted in accordance with the Hansen parameters of the separation target (liquid such as an organic solvent).
Below, taking the case of using two kinds of acrylic monomers of (a) methyl acrylate and (b) acrylamide as an example,
The affinity of the acrylic graft copolymer for various solvents will be described. In the Hansen parameters,
Since δ _d changes little for many solvents, δ _p ,
It is described by two-dimensional coordinates of [delta] _h.

Parameters unique to polymethyl acrylate (corresponding to the coordinates of the center of circle 1) are represented by coordinates δ _p −
It exists on the horizontal axis near (9,5) at [delta] _h. In contrast, a circle 3 plotting the Hansen parameters of polyacrylamide (hydrophilic and insoluble in most organic solvents) is located near water. Further, the circle 2 defined by the Hansen parameter of the copolymer obtained by blending methyl acrylate and acrylamide is located between the circles 1 and 3.

For example, a separation membrane having polymethyl acrylate (homopolymer) in pores (circle 1 in FIG. 1)
Is used, a solvent having a Hansen parameter inside the circle 1 (for example, acetone) and a solvent having a Hansen parameter outside the circle 1 (for example, methanol)
Can be separated from a mixture of acetone and acetone, but it is difficult to separate acetone from a mixture of acetone and another solvent having a Hansen parameter inside circle 1 (eg, benzene).

On the other hand, when a separator having polyacrylamide (homopolymer) in the pores (corresponding to circle 3 in FIG. 1) is used as the separation membrane, for example, separation of water and methanol is possible. It is difficult to separate two solvents having both Hansen parameters inside.

Therefore, in the present invention, methyl acrylate and methyl acrylate are mixed so that only the Hansen parameters of the solvent to be separated fall within the circle (sphere) shown in FIG. 1 in consideration of the Hansen parameters of each solvent in the mixed solvent. An acrylic graft copolymer is formed by setting the mixing ratio with acrylamide. For example, when trying to separate methanol and isopropyl alcohol, the mixing ratio of methyl acrylate and acrylamide is changed so that the circle formed by the copolymer is slightly above circle 2.

As can be seen from FIG. 1, when the graft copolymer contains a large amount of methyl acrylate (the portion near circle 1), the separation membrane is suitable for separating acetone or the like, but the graft copolymer is made of acrylamide. As more is included, it becomes more suitable for selectively separating solvents such as alcohols. Further, when the amount of acrylamide increases, the separation property from water becomes better. Thus, by changing the ratio of acrylamide in the graft copolymer,
The combination of solvents that can be separated changes.

As described above with reference to the above-mentioned two types of acrylic monomers of methyl acrylate and acrylamide,
If the graft copolymer is formed so as to match the object to be separated, good separation can be performed for various liquid mixtures. Here, the separation membrane selectively permeates only a liquid that is soluble in the graft copolymer filling the micropores, but the swelling is suppressed as a whole membrane, the membrane is not deformed, and the membrane is not deformed. No reduction in strength occurs.

In the present invention, the graft copolymer is formed on the inner surface of the pores of the microporous membrane as described above, and a plasma graft polymerization method is used for this. In the plasma graft polymerization method, a microporous ultra-high molecular weight polyethylene membrane is irradiated with plasma to generate radicals, and then a plurality of monomers are brought into contact with the microporous membrane to perform graft polymerization.

As the plasma graft polymerization, there are a gas phase polymerization method and a liquid phase polymerization method, and the liquid phase polymerization method is preferable for graft polymerization of a monomer. In this liquid-phase polymerization method, a mixture of a plurality of types of acrylic monomers is simultaneously prepared.
Alternatively, it can be carried out by sequentially contacting each of them.

By generating radicals in the microporous film serving as the base material and performing graft polymerization instead of the monomers to be graft-polymerized, the monomers can be graft-polymerized to the inner surfaces of the pores. The homopolymer formed at that time is preferably washed away with a solvent. Although the graft copolymer is formed on the surface other than the inner surface of the pores of the ultrahigh molecular weight polyethylene microporous membrane, it is desirable to minimize the graft copolymer.

FIG. 2 is a partial cross-sectional perspective view conceptually showing a process of forming a separation membrane of the present invention by subjecting a monomer to the microporous polyethylene membrane 4 by plasma graft polymerization. As shown in (a), the microporous polyethylene membrane 4 has many pores 5 penetrating the membrane. Plasma graft polymerization is performed on the microporous film, and a plurality of monomers are graft-polymerized on the surface. In FIG. 2, the copolymer 6 graft-copolymerized as shown in FIG. 2 (b) is formed not only on the surface of the microporous membrane but also on the inner surface of the pores. 1 shows one embodiment of a membrane substantially filled with.
In this figure, the graft polymer 3 is formed on both sides of the microporous membrane 4, but the present invention is not limited to this, and the graft copolymer 3 extends to one side of the polyethylene microporous membrane 4 and part of the pores. 6 may be formed.

The homopolymer by-produced in the course of the plasma graft polymerization is completely washed away using a solvent such as toluene, and only the graft polymer is removed on the surface of the polyethylene microporous membrane (inner pore surface and membrane surface). Leave.

The plasma graft polymerization specifically includes the following steps.

(A) argon at a pressure of 10 ^{-2 to} 10 mbar,
Normal frequency in the presence of gas such as helium, nitrogen, air
A plasma treatment is performed on the microporous film at 10 to 30 MHz and output of 1 to 1000 W for 1 to 1000 seconds.

(B) The plasma-processed microporous membrane is converted into an inorganic or organic solvent (a concentration of each of the monomers to be used is appropriately determined in consideration of the above-mentioned Hansen parameters) by using a plurality of monomers as necessary. The graft polymerization reaction is carried out at 20 to 100 ° C. for 1 minute to several days depending on the combination of monomers while immersing in a dissolved or suspended solution, particularly in an aqueous solution, and bubbling nitrogen gas, argon gas, etc., depending on the combination of monomers.

(C) The obtained microporous membrane is washed with toluene, xylene, etc. for about one hour and dried.

By the above-described plasma graft polymerization method, it is possible to obtain a target separation membrane in which the pores of the microporous membrane are substantially closed with the graft copolymer. Since plasma graft polymerization occurs only on the surface of the microporous polyethylene membrane, it does not degrade the membrane substrate. Further, since the graft copolymer is chemically bonded to the film substrate, it does not change with time.

In the separation membrane of the present invention, it is necessary that the graft copolymer substantially fills the pores of the polyethylene microporous membrane as the membrane base material. The pore-filled graft copolymer selectively takes up certain components of the liquid mixture and permeates them to the other side of the membrane. Since the porosity of the polyethylene microporous membrane is high, the amount of the substance permeating (separating) through the graft copolymer in the pores increases, and efficient separation can be performed. In addition, since the swelling of the graft copolymer is suppressed by the polyethylene microporous membrane, the strength of the entire membrane does not decrease.

Next, a separation method using the above-described separation membrane of the present invention will be described.

In the method of the present invention, an organic solvent mixture is separated by a pervaporation method, a reverse osmosis method or an evaporation method using the separation membrane of the present invention described so far. The pervaporation method, the reverse osmosis method or the evaporation method in the method of the present invention includes:
Except for using the separation membrane of the present invention, it is basically the same as the known pervaporation, reverse osmosis method or evaporation method, and is separated on the primary side through the separation membrane of the present invention. The mixed liquid or vapor is supplied, the secondary side is set to the low pressure side, and one component of the mixed liquid is taken out to the secondary side as gas or liquid.

The application temperature range in the separation method of the present invention is usually 0 to 120 ° C., preferably 10 to 100 ° C. If the temperature exceeds 120 ° C, the heat resistance of the microporous polyethylene membrane becomes insufficient, causing problems in maintaining the membrane shape. If the temperature is lower than 0 ° C, depending on the separation target, the unit membrane area and film thickness are generally large. In addition, the amount of permeation per unit time decreases, which is not preferable.

The pressure range applicable to the separation method of the present invention is 200 kg / cm ² or less, preferably 100 kg / cm ² or less. At a pressure exceeding 200 kg / cm ² , it becomes difficult to maintain the shape of the microporous polyethylene membrane.

The liquid mixture that can be separated by the method of the present invention includes water, aliphatic alcohols, ketones such as acetone, and the like.
Examples thereof include aliphatic hydrocarbons, aromatic hydrocarbons such as benzene and toluene, halogenated hydrocarbons such as carbon tetrachloride, and one or a mixture of two or more of cyclohexanol, tetrahydrofuran, and tetrahydrofurfural.

[0064]

The present invention will be described in more detail with reference to the following specific examples.

Example 1 Weight average molecular weight 2 × 10 ⁶ , film thickness 5 μm, porosity 70%,
Plasma is applied to a microporous ultrahigh molecular weight polyethylene membrane (manufactured by Tonen Chemical Co., Ltd .: molecular weight cut off: 200,000) having an average pore size of 0.02 μm and a breaking strength of 700 kg / cm ² using a plasma generator (manufactured by Samco Corporation) Irradiated. Table 1 shows the conditions of the plasma treatment at this time.

[0066]

Next, the plasma treated ultra-high molecular weight polyethylene microporous membrane was mixed with various ratios of aqueous solutions of mixed monomers of methyl acrylate and acrylamide (concentration of the mixed monomers of 5% by weight) at a mixing ratio of 5 to 5%. Dipped for 60 minutes. The temperature of the aqueous solution during immersion was 30 ° C.

After immersion, the ultrahigh molecular weight polyethylene microporous membrane was washed in toluene for one day and dried at room temperature. After drying, the weight of the film was measured, and the amount of graft polymerization was measured based on the change from the initial film weight, so that the polymerization amount was kept constant at about 2 mg / cm ² .

Each of the obtained films became transparent after the reaction,
It was confirmed that the pores in the substrate were filled with the graft copolymer. In addition, the obtained copolymer film was analyzed by a transmission type and a total reflection type Fourier transform type IR method, and as a result of comparing the composition of the entire film and the surface composition, methyl acrylate and acrylamide were copolymerized in the pores of the film. I confirmed that.
Further, the composition of the graft copolymer was evaluated by elemental analysis.

Using this separation membrane, a sorption test was conducted on five kinds of solvents, methanol, isopropanol, acetone, benzene and carbon tetrachloride. In this test, 25
The sorption weight ratio (weight of liquid (g) / weight of film (g)) was determined by comparing the weight of the film swollen by immersion in each organic solvent at 20 ° C. for 20 hours or more and the dry weight before immersion. . The results are shown in FIG.

For reference, a separation membrane in which a polyacrylamide homopolymer was disposed in the pores of the above-described microporous membrane and a separation membrane in which a polymethyl acrylate homopolymer was disposed were prepared.

The two types of separation membranes were subjected to sorption tests for each solvent in the same manner as described above. The results are shown in FIG.

As can be seen from FIG. 3, as the polyacrylamide component in the graft copolymer increases, the solubility of benzene, carbon tetrachloride and acetone decreases. Also,
The solubility of methanol and isopropanol showed maximum values when the polyacrylamide component was around 40% by weight. This is consistent with the prediction obtained from FIG. 1 shown above.

Example 2 In the same manner as in Example 1, a plurality of separation membranes were prepared by graft copolymerization of methyl acrylate and acrylamide having various compositions.

Using this membrane, a pervaporation permeation experiment was performed with a single component of methanol and acetone.
The temperature of the permeate (methanol and acetone) was 25
° C. FIG. 4 shows the results.

For reference, a pervaporation permeation experiment was carried out using methanol and acetone as a single component in the same manner as described above, using a separation membrane whose pores were closed by a polymethyl acrylate homopolymer. The results are shown in FIG.

As can be expected from FIG. 1, the permeation flux of acetone decreased as the polyacrylamide component in the acrylic graft copolymer increased. Also, methanol showed a maximum value when the polyacrylamide component was around 40% by weight.

As can be seen from the above, the present invention can cope with the separation of a wide range of liquid mixtures by changing the composition of the graft copolymer of the separation membrane.

[0079]

The separation membrane of the present invention uses a microporous polyethylene membrane as a base material and has good swelling resistance in an organic solvent. In particular, when ultra-high molecular weight polyethylene is used as the polyethylene, the separation membrane has excellent mechanical strength and durability. Further, separation with good reproducibility can be performed.

In the separation membrane of the present invention, since the acrylic graft copolymer substantially blocks the pores of the microporous membrane, the pervaporation method, the reverse osmosis method, or the evaporation method is used. By using this, a liquid having an affinity for the copolymer can be separated with high selectivity.

In the method of the present invention, the composition of the copolymer is set as desired by estimating the affinity between the composition of the copolymer and the substance to be separated in consideration of the Hansen parameters of the components in the mixed liquid. And a reliable and selective separation can be achieved.

The separation membrane according to the present invention is suitably used for separation of a liquid mixture such as an organic solvent by a pervaporation method, a reverse osmosis method, or an evaporation method.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing a measure of the affinity between various solvents and a copolymer using Hansen parameters, showing a change in components in the copolymer and a change in affinity with a solvent.

FIG. 2 is a partial cross-sectional perspective view conceptually showing a step of plasma graft copolymerizing a monomer onto a polyethylene microporous membrane, wherein (a) shows a polyethylene microporous membrane and (b) has a graft copolymer. 1 shows a microporous polyethylene membrane.

FIG. 3 is a graph showing the results of a solvent sorption test in Example 1.

FIG. 4 is a graph showing the results of a solvent permeation test in Example 2.

[Explanation of symbols]

 4: Microporous polyethylene membrane 5: Pores 6: Graft copolymer

────────────────────────────────────────────────── (5) References JP-A-3-98632 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 71/78 B01D 61/02 B01D 61 / 36 B01D 71/26 B01D 71/40

Claims (6)

(57) [Claims] 1. A method for performing plasma graft polymerization on a polyethylene microporous membrane using a plurality of types of monomers having different solubilities, wherein pores of the microporous membrane are substantially filled with a produced graft copolymer. The mixture ratio of the monomer is such that the liquid or vapor to be separated in the mixed liquid is
A mixed liquid or vapor separation membrane characterized in that it is selected so as to be a good solvent for the produced graft copolymer and to be a poor solvent for the others. 2. The separation membrane according to claim 1, wherein the solubility is represented by a solubility parameter or a χ parameter. 3. The separation membrane according to claim 2, wherein the solubility parameter is represented by a Hansen parameter. 4. The separation membrane according to claim 1, wherein the graft copolymer comprises (a) acrylic acid, methacrylic acid or an ester thereof, and (b) acrylamide or a derivative thereof. A mixed liquid or vapor separation membrane, which is a graft copolymer of two kinds of acrylic monomers. 5. The separation membrane according to claim 4, wherein the (a) species of the acrylic monomer is methyl acrylate, and the (b) species is acrylamide. Membrane. 6. A method for selectively separating a specific liquid or vapor from a mixed liquid or vapor by a pervaporation method, a reverse osmosis method, or an evaporation method,
A polyethylene microporous membrane, using a separation membrane that substantially fills the pores of the microporous membrane with a graft copolymer by performing plasma graft polymerization using a plurality of types of monomers having different solubility, At this time, the compounding ratio of the monomers is selected so that the specific liquid or vapor in the mixed liquid or vapor becomes a good solvent for the produced graft copolymer, and the others become poor solvents. A method for separating a liquid or vapor mixture.