JP3219298B2 - 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 an organic solvent mixture, and more particularly to the separation of an organic solvent having a high affinity for an acrylic polymer from an organic solvent having a low affinity for an acrylic polymer. And a separation method using the separation membrane.

[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 an organic solvent by a membrane separation method is also one of the fields in which attention has been paid. Mixtures which could not be separated by a simple method in the past (for example, a mixture having a boiling point close to and difficult to separate by distillation, Azeotropic mixtures, mixtures containing heat-sensitive substances, etc.) are being studied as a method for separating or concentrating. The pervaporation method and the reverse osmosis method are suitable for the membrane separation method of a mixture of organic solvents.

[0004] The accuracy and efficiency of separation in membrane separation methods including the pervaporation method and the reverse osmosis method are as follows.
Since it depends on the performance of the membrane itself, it is important to develop a membrane having excellent strength, durability and separation selectivity, and various polymer membranes have been proposed so far.

For example, Japanese Patent Application Laid-Open No. 50-98568 discloses a permeable membrane in which a polymerizable monomer is graft-aggregated on the inner surface of a pore of a polymer film having pores. This permeable membrane uses a polymer polymer film having pores such as polyethylene, which has excellent durability, heat resistance and chemical resistance, as a base material. Graft polymerized on the inner surface. However, this separation membrane is suitable for separating an aqueous mixture by a reverse osmosis method, but its performance is not sufficient in separating an organic solvent-based mixture such as a benzene / cyclosexane mixture.

JP-A-52-122279 discloses a separation membrane comprising an aliphatic olefin polymer containing an acid group derived from an unsaturated carboxylic acid or the like. In this separation membrane, an unsaturated carboxylic acid or the like is polymerized on the surface of a membrane substrate made of an aliphatic olefin polymer or the like by a radical reaction, a crosslinking reaction by light irradiation or electron beam irradiation. This separation membrane can be used for a pervaporation method, and in particular, an unsaturated compound can be relatively easily separated from a mixture of organic solvents. However, the performance of the membrane is not yet sufficient such that the membrane is practically used on a porous support.

In order to obtain an excellent separation membrane, it is basically 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.

Therefore, a separation membrane comprising a composite membrane having a structure in which pores of the membrane are substantially filled with a polymer using a microporous membrane made of a material which 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 and separates only specific components by passing through the pores filled with the polymer.

As such a separation membrane, JP-A-3-98632
Discloses an acrylic polymer obtained by graft-polymerizing an acrylic monomer onto a microporous polyethylene membrane and substantially filling the pores with an acrylic graft polymer. This separation membrane can satisfactorily separate benzene from a benzene / cyclohexane mixture, for example, with high selectivity. However, according to the study of the present inventors, when this separation membrane is applied to a reverse osmosis method, the separation selectivity is not good.

Accordingly, an object of the present invention is to provide a separation membrane which can separate a specific organic substance from various organic mixtures with high selectivity and is excellent in strength and durability.

It is another object of the present invention to provide a separation method having high selectivity to an organic solvent mixture.

[0012]

Means for Solving the Problems In view of the above object, as a result of intensive studies, the present inventors have found that the surface of a microporous polyethylene film has two or more double bonds in an acrylic monomer and a molecule.
By performing a plasma graft polymerization using a crosslinkable monomer having a separation membrane in which the pores of the microporous membrane are substantially closed with an acrylic graft crosslinked polymer, the affinity for the acrylic graft crosslinked polymer is increased. Have been found to be able to selectively permeate the organic solvent having, and have good strength and durability of the separation membrane, and can be applied not only to the pervaporation method but also to the reverse osmosis method. completed.

That is, the separation membrane of the present invention used for separating an organic solvent mixture is obtained by plasma graft polymerization of an acrylic monomer and a crosslinkable monomer having two or more double bonds in a molecule on a polyethylene microporous membrane.
Separation membrane on which a crosslinked graft polymer is formed,
The acrylic graft-crosslinked polymer is used to form the microporous membrane.
It is characterized in that the pores are filled .

In a preferred embodiment, the polyethylene microporous membrane serving as a base material of the separation membrane has a weight average molecular weight of 5 × 10 5
^A microporous membrane made of ⁵ or more ultrahigh molecular weight polyethylene,
Thickness 0.1 ~ 50μm, porosity 30 ~ 95%, average pore diameter 0.005 ~
A material having a breaking strength of 1 μm and a breaking strength of 400 kg / cm ² or more is used.

Further, the method of the present invention for separating an organic solvent mixture is characterized in that the above-mentioned method is carried out by subjecting a polyethylene microporous membrane to plasma graft polymerization using an acrylic monomer and a crosslinkable monomer having two or more double bonds in a molecule. Using a separation membrane in which the pores of the microporous membrane are filled with an acrylic graft-crosslinked polymer, an organic solvent having an affinity for the acrylic graft-crosslinked polymer is selectively obtained by a pervaporation method or a reverse osmosis method. It is characterized by being separated.

Hereinafter, the present invention will be described in detail. First, the separation membrane 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 or a polyethylene composition containing ultrahigh molecular weight polyethylene can be used, but those made of ultrahigh molecular weight polyethylene are preferable from the viewpoint of strength and the like.

When a microporous membrane made of ultrahigh molecular weight polyethylene is used as the base material of the separation membrane, the ultrahigh molecular weight polyethylene used as the material is a homopolymer of ethylene or a mixture of ethylene and 10 mol% or less of α-olefin. It is a crystalline linear ultra-high molecular weight polyethylene made of a copolymer. As for the molecular weight, the weight average molecular weight is 5 × 10 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.

As the material of the ultrahigh molecular weight polyethylene microporous membrane, in addition to the above, a material obtained by blending another relatively high molecular weight polyethylene with 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. If 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 during dissolution is 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.

In such a polyethylene composition,
As described above, the content of the ultrahigh molecular weight polyethylene is preferably 1% by weight or more based on 100% by weight of the entire polyethylene composition. Ultra high molecular weight polyethylene content of 1
If it is less than 10% by weight, almost no entanglement of the molecular chain of the ultra-high molecular weight polyethylene contributing to the improvement of stretchability is formed,
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 ultra-high molecular weight polyethylene microporous membrane, whether used alone or in the case of a composition, may optionally 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.

Next, a method for producing a microporous ultrahigh molecular weight polyethylene membrane will be described. First, in the case of a microporous membrane made of ultra-high molecular weight polyethylene alone, for example, JP-A-60-242
It can be produced by the method described in No. 035.

Next, in the case of a microporous membrane made of a polyethylene composition obtained by blending ultrahigh molecular weight polyethylene with relatively high 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. Heat 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 0-250 ° C. At this time, the extrusion speed is usually
20-30 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 defined as 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, 90-140 ° C., more preferably 10
It ranges from 0 to 130 ° C.

The thickness of the polyethylene microporous membrane serving as the base material of the separation membrane is preferably 0.1 to 50 μm, more preferably 0.2 to 25 μm. When the thickness is less than 0.1 μm, the mechanical strength of the film is small, and it is difficult to put the film to 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.

The porosity of the microporous membrane is preferably 30 to 95%, more preferably 50 to 90%. Porosity of 30
%, The permeability of the separation target is insufficient, while 95%
%, The mechanical strength of the film 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, the permeability of the target substance for separation becomes insufficient, and
If it exceeds μm, the separation performance will decrease.

Further, by setting the breaking strength to 400 kg / cm ² or more, deformation resistance against swelling when a solvent is dissolved in an acrylic graft crosslinked polymer formed in pores (this will be described later). Is sufficient.

In the separation membrane of the present invention, an acrylic monomer and a crosslinking monomer having two or more double bonds in the molecule are graft-crosslinked and polymerized on at least the inner surface of the pores of the above-mentioned polyethylene microporous membrane. The acrylic graft crosslinked polymer has a structure in which pores are substantially closed.
Here, "grafted and cross-linked" means that the so-called graft copolymers (polymers having long molecular chains and branched molecular chains bonded) are further cross-linked and polymerized. The graft crosslinking polymerization using an acrylic monomer and a crosslinking monomer is performed by a plasma graft polymerization method as described later.

As the acrylic monomer, acrylic acid,
Methacrylic acid, acrylic acid ester, acrylamide,
Acrylonitrile, methacrylic acid ester, and the like can be used, and are appropriately selected depending on the separation target.

The crosslinkable monomer has two or more double bonds in the molecule, and is capable of polymerizing itself to form a molecular chain and providing a site for crosslinking with another molecular chain. . Such crosslinkable monomers include:
Vinyl acrylate, vinyl methacrylate, divinylbenzene, vinyl butyl acrylate, and the like can be used. In addition, it is preferable to use an acrylic monomer as the crosslinkable monomer, but other crosslinkable monomers can also be used. The crosslinkable monomer is appropriately set in consideration of the type of the separation target and the acrylic monomer.

The mixing ratio of the acrylic monomer and the crosslinkable monomer in the graft crosslinking polymerization is appropriately adjusted depending on the kind of the monomer to be used, the intended use of the separation membrane, and the type of the object to be separated. The ratio is preferably set to 2: 1.

Further, in the present invention, a third polymerizable monomer may be added in addition to the acrylic monomer and the crosslinkable monomer described above. By further adding a third monomer that can be polymerized with the acrylic monomer, a substance that does not have a high affinity for a homopolymer of the acrylic monomer or a copolymer of the acrylic monomer and the crosslinkable monomer can also be separated. In other words, if a third monomer having a high affinity for the separation target is introduced to form a copolymer in which the separation target has a high affinity, those having a low affinity for the acrylic polymer may be used. It becomes separable.

When a (crosslinkable) copolymer using such a third monomer is formed in the pores of a microporous polyethylene membrane, the solubility of the copolymer in the separation target is taken into consideration. It is preferable to determine the third monomer species and the compounding amount thereof.

When a separation membrane of a benzene / cyclohexane mixture is used, graft polymerization is preferably carried out using methyl acrylate as an acrylic monomer and vinyl acrylate or divinylbenzene as a crosslinkable monomer. Polymethyl acrylate-based polymers have an affinity for benzene and tend to swell when benzene dissolves, but because deformation is suppressed by crosslinking with the polyethylene microporous membrane (at the graft polymerization section),
Dissolution diffusion due to the plasticizing effect of cyclohexane having no affinity is suppressed. Therefore, only benzene passes through the graft-crosslinking polymerization section formed in the pores, and the separation membrane selectively permeates benzene from the benzene / cyclohexane mixture. In the pores,
The swelling of the cross-linked polymethyl acrylate polymer with benzene is suppressed, the entire film is hardly deformed, and the strength of the film does not decrease.

For the production of a separation membrane for a mixed solution of chloroform / n-hexane, it is preferable to carry out graft polymerization using methyl acrylate as an acrylic monomer and vinyl acrylate as a crosslinkable monomer.

In the present invention, a graft crosslinked polymer is formed on the inner surface of the pores of the microporous membrane by using an acrylic monomer and a crosslinkable monomer by a plasma graft polymerization method. In the plasma graft polymerization method, a microporous polyethylene membrane is irradiated with plasma to generate radicals, and then an acrylic monomer and a crosslinkable monomer 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 a liquid phase polymerization method is preferable for performing graft polymerization using an acrylic monomer. In this way, the acrylic monomer can be graft-crosslinked and polymerized to the inner surface of the pores by generating radicals on the microporous film serving as the base material and performing graft polymerization on the microporous film as the base material, not on the side of the acrylic monomer to be graft-polymerized. The homopolymer formed at that time is washed away with a solvent. In addition, a graft polymer is formed on the surface other than the inner surface of the pores of the polyethylene microporous membrane. However, since the graft polymer substantially affects the permeability, it is desirable to minimize the graft polymer.

FIG. 1 is a schematic sectional view conceptually showing a process for producing a separation membrane of the present invention by plasma graft polymerization of an acrylic monomer and a crosslinkable monomer on a polyethylene microporous membrane 1. As shown in FIG. 1A, the microporous polyethylene membrane 1 has a large number of pores 2 penetrating the membrane.
The microporous membrane is subjected to plasma graft polymerization using an acrylic monomer and a crosslinkable monomer to form a graft crosslinked polymer on the surface. The acrylic crosslinked polymer 3 obtained by the graft crosslinking polymerization is formed not only on the surface of the microporous membrane but also on the inner surface of the pores. (b-1) shows one embodiment of a membrane in which the pores are substantially filled with the graft polymer 3. In (b-2), the graft crosslinked polymer 3 is formed on one surface of the microporous membrane. Here, the graft-crosslinked polymer 3 is formed to a part of the pores,
Is closed. The separation membrane of the present invention may have either of these structures.

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 comprises the following steps. (a) In the presence of a gas such as argon, helium, nitrogen, or air having a pressure of 10 ^{-2 to} 10 mbar, a normal frequency of 10 to 30 MHz, an output of 1 to 1000 W, and a power of 1 to 1000 seconds for a microporous membrane. Plasma treatment is performed. (b) An inorganic or organic solvent containing 1 to 10% by volume of an acrylic monomer and 0.01 to 2% by volume of a crosslinkable monomer (the acrylic monomer and the crosslinkable monomer are dissolved or suspended in this solvent) is subjected to plasma treatment. Dipped microporous membrane and bubbling nitrogen gas, argon gas, etc.
The graft polymerization reaction is performed at 0 ° C. for 1 to 60 minutes. In this step, each monomer undergoes cross-linking polymerization. In addition, as a solvent, water, alcohol such as methanol, an alcohol aqueous solution, or the like can be used. (c) The obtained microporous membrane is washed with toluene, xylene or the like for about 1 hour and dried.

By the plasma graft polymerization method described above, a separation membrane in which the crosslinked acrylic graft polymer substantially closes the pores of the microporous membrane can be obtained.
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 crosslinked polymer is chemically bonded to the membrane substrate, it does not change with time.

In the separation membrane of the present invention, it is necessary that the pores of the polyethylene microporous membrane serving as the membrane base material are filled with a crosslinked acrylic graft-crosslinked polymer. The pore-blocked acrylic graft cross-linked polymer selectively takes up certain components of the organic solvent 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) the acrylic graft-crosslinked polymer in the pores is increased, and efficient separation can be performed. In addition, since the swelling of the acrylic graft polymer itself is suppressed by the cross-linking of the microporous polyethylene membrane and the graft polymer, 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, the organic solvent mixture is separated by the pervaporation method or the reverse osmosis method using the separation membrane of the present invention described in detail above. The pervaporation method or reverse osmosis method in the method of the present invention is basically the same as the known pervaporation or reverse osmosis method except that the separation membrane of the present invention is used.

In the pervaporation, a mixed liquid to be separated is supplied to the primary side through the separation membrane of the present invention,
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. For example, when a benzene / cyclohexane mixture is separated on a microporous polyethylene membrane by a separation membrane obtained by performing plasma graft polymerization using methyl acrylate and vinyl acrylate, benzene is gaseous or liquid on the secondary side. Is taken out as

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 shape of the membrane. If the temperature is less than 0 ° C., the permeation amount per unit film area, film thickness and time decreases. Not preferred.

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 is difficult to maintain the shape of the ultrahigh molecular weight polyethylene microporous membrane.

The organic liquid mixture which can be separated with high selectivity by the method of the present invention includes aromatic hydrocarbons such as benzene and toluene, chlorinated hydrocarbons, tetrahydrofuran, aliphatic alcohols, aliphatic hydrocarbons, acetone and the like. And mixtures of two or more of such ketones, cyclohexanol, and tetrahydrofurfural. Specifically, the above-mentioned benzene / cyclohexane,
In addition to benzene / n-hexane, benzene / n-heptane, toluene / cyclohexane, toluene / methylcyclohexane, hexane / heptane, toluene / benzene and the like can be mentioned. In addition, benzene / water, chlorine-based organic solvent / water, etc. Mixtures with different solubility parameters (organic solvents) are mentioned.

[0056]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A microporous ultrahigh molecular weight polyethylene membrane (manufactured by Tonen Chemical Co., Ltd.) having a weight average molecular weight of 25 × 10 ⁵ , a film thickness of 10 μm, a porosity of 70%, an average pore diameter of 0.02 μm, and a breaking strength of 4700 kg / cm ^{2 was} prepared. Plasma irradiation was performed using a plasma polymerization apparatus (manufactured by Samco Corporation). Table 1 shows the conditions of the plasma treatment at this time.

[0057]

Next, the plasma-treated ultra-high molecular weight polyethylene microporous membrane was treated with 4 wt% methyl acrylate.
Then, it was immersed for 15 minutes in a methanol aqueous solution (methanol: water = 10: 90) in which vinyl acrylate became 1 wt%.
The temperature of the aqueous methanol solution at the time of 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 membrane was measured, and the amount of graft polymerization was measured based on the change from the initial membrane weight. The polymerization amount was 2.07 mg / cm ² .

Using this separation membrane, chloroform / n-hexane (72 wt%: 28 wt%) was obtained by pervaporation.
An experiment of separating the mixed solution was performed. Assuming that the temperature of the supply liquid was 25 ° C., the permeation flux (Q) and the separation coefficient (α) at that time were determined. The permeation flux (Q) was 1.7 kg / m ² hr and the separation factor (α) was 21.

Example 2 In the same manner as in Example 1, a microporous ultrahigh molecular weight polyethylene membrane was subjected to plasma graft polymerization using methyl acrylate and vinyl acrylate to obtain a separation membrane.

The temperature of the feed solution (mixed solution of chloroform (72 wt%) / n-hexane (28 wt%)) was set at 25 ° C.
Separation experiments were performed by the reverse osmosis method. Operating pressure is 80kg / cm ²
And At this time, the permeation flux (Q) and the separation coefficient (α)
I asked. The results are shown in FIG.

Comparative Example 1 A separation membrane was prepared in the same manner as in Example 2 except that vinyl acrylate as a crosslinking monomer was not used. In this separation membrane, the polymer formed in the pores is not crosslinked.

A separation experiment by a reverse osmosis method was performed under the same conditions as in Example 2 (operating pressure: 80 kg / cm ² ). However, under these conditions, the separation membrane of Comparative Example 1 did not substantially perform selective permeation separation.

As can be seen from the above, the separation membranes of the examples show higher separation performance in separation of an organic liquid mixture such as chloroform / n-hexane by the pervaporation method than the conventional separation membranes.

Further, it is possible to separate an organic liquid mixture by a reverse osmosis method, which was impossible in the past. The separation membrane of the present invention can be applied to both pervaporation and reverse osmosis.

[0067]

The separation membrane of the present invention has good swelling resistance in an organic solvent, and has excellent mechanical strength and durability.

Further, in the separation membrane of the present invention, since the acrylic graft crosslinked polymer substantially blocks the pores of the microporous membrane, the grafting is carried out by using a pervaporation method or a reverse osmosis method. Organic substances having an affinity for the polymer can be separated with high selectivity.

Such a separation membrane is suitably used for separation of an organic solvent mixture by a pervaporation method or a reverse osmosis method. In particular, separation of a chloroform / n-hexane mixture or a benzene / cyclohexane mixture, or It is useful for separating organic solvent components contained in trace amounts in water.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view conceptually showing a step of plasma-grafting an acrylic monomer onto a polyethylene microporous membrane, wherein (a) shows a polyethylene microporous membrane, and (b-1) and (b-2) Represents a microporous polyethylene membrane graft-polymerized.

FIG. 2 is a graph showing a relationship between a permeation flow rate and a separation coefficient of a separation membrane of Example 2 and a reverse osmosis operation time.

[Explanation of symbols]

 1 Microporous polyethylene membrane 2 Pores 3 Graft cross-linked polymer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 71/00-71/82

Claims (5)

(57) [Claims] 1. Acrylic monomer by plasma graft polymerization of an acrylic monomer and a crosslinkable monomer having two or more double bonds in a molecule onto a polyethylene microporous membrane .
A separation membrane on which a raft crosslinked polymer is formed, wherein
Pores of the microporous membrane by a cryl graft graft polymer
A separation membrane for an organic solvent mixture, wherein the separation membrane is filled . 2. The separation for an organic solvent mixture according to claim 1.
In the film, the acrylic monomer: the crosslinkable monomer
-The compounding weight ratio is 1000: 1 to 2: 1
Separation membrane for organic solvent mixtures. 3. The organic solvent mixture according to claim 1 or 2.
In the separation membrane for use, the acrylic monomer is acrylic
Acid, methacrylic acid, acrylate, acrylamide
, Acrylonitrile and methacrylic acid esters.
At least one selected from the group consisting of
Nomer is vinyl acrylate, vinyl methacrylate,
Group consisting of divinylbenzene and vinyl butyl acrylate
At least one member selected from the group consisting of
Separation membrane for organic solvent mixture. 4. The organic solvent according to claim 1,
In the separation membrane for a medium mixture, the acrylic monomer is
Organic solvent mixture characterized by tyl acrylate
Material separation membrane. In the method of separation wherein an organic solvent mixture, the polyethylene microporous membrane acrylic monomers and in the molecule in two
Acrylic graft crosslinked polymer by plasma graft polymerization of crosslinkable monomer having two or more heavy bonds
Wherein the acrylic graft is formed.
Using <br/> separation membrane pores of the microporous membrane by cross-linked polymer is filled, by pervaporation method or reverse osmosis organic solvent having an affinity for the acrylic graft crosslinked polymer A method for separating an organic solvent mixture, wherein the mixture is selectively permeated .