JPH05237352A - Separation membrane and separation - Google Patents

Abstract

PURPOSE:To provide a separation membrane which highly selectively separates the specified organic material from various kinds of organic mixtures and is excellent in strength and durability. CONSTITUTION:A polyethylene narrow porous membrane 1 is given plasma graft polymerization with an acrylic monomer and a crosslinkable monomer and narrow pores 2 of fine porous membrane 1 are practically clogged by an acrylic graft crosslinked polymer 3 to form a separation membrane for organic solvent mixing.

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 particularly to separating an organic solvent having a high affinity with an acrylic polymer from an organic solvent having a low affinity with an acrylic polymer. And a separation method using the separation membrane.

[0002]

2. Description of the Related Art Membrane separation methods for separating various mixtures using a membrane having pores include
In recent years, it has become more and more popular, and its technology is being applied in various fields. Also, the separation target in the membrane separation method is solid
There is much interest in developing separation membranes and separation techniques for various mixtures over a wide range, not only liquid mixtures, but also liquid-liquid, gas-gas, gas-liquid mixtures.

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

By the way, the accuracy and efficiency of separation in the membrane separation method 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 excellent in strength, durability and separation selectivity, and various polymer membranes have been proposed so far.

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

Further, JP-A-52-122279 discloses a separation membrane composed of an aliphatic olefin polymer containing an acid group derived from an unsaturated carboxylic acid or the like. In this separation membrane, 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 in a pervaporation method, and in particular, an unsaturated compound can be separated relatively easily from a mixed solution of organic solvents. However, the performance of the membrane is still insufficient in practical use, for example, by placing it 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 will swell and a high separation selectivity cannot be obtained due to the plasticizing effect. In addition, the mechanical strength and durability of the separation membrane may be deteriorated.

Therefore, a separation membrane made of a composite membrane having a structure in which a microporous membrane made of a material that does not swell in an organic solvent is used as a substrate and the pores of the membrane are substantially filled with a polymer has been developed. There is. Here, the polymer that fills the pores has a good affinity for the object to be separated, and while the swelling of the entire membrane is suppressed, only the specific component is separated by passing through the pores filled with the polymer.

As such a separation membrane, Japanese Patent Laid-Open No. 3-98632
JP-A No. 1994-242242 discloses a polyethylene microporous membrane in which an acrylic monomer is graft-polymerized and the pores are substantially filled with an acrylic graft polymer. This separation membrane can separate benzene favorably with high selectivity, for example from a benzene / cyclohexane mixture. However, according to the study of the present inventors, when this separation membrane is applied to the reverse osmosis method, the separation selectivity is not good.

Therefore, an object of the present invention is to provide a separation membrane capable of separating a specific organic substance from various organic mixtures with high selectivity and having excellent strength and durability.

Another object of the present invention is to provide a separation method with high selectivity for an organic solvent mixture.

[0012]

As a result of earnest research in view of the above object, the present inventor has found that by performing plasma graft polymerization on the surface of a polyethylene microporous membrane using an acrylic monomer and a crosslinkable monomer, By using a separation membrane in which the pores of the porous membrane are substantially clogged with an acrylic graft-crosslinked polymer, an organic solvent having an affinity for the acrylic graft-crosslinked polymer can be selectively permeated, and the separation membrane is also separated. The present invention was completed by discovering that it has good strength and durability and can be applied not only to the pervaporation method but also to the reverse osmosis method.

That is, the separation membrane of the present invention used for separating an organic solvent mixture is obtained by subjecting a polyethylene microporous membrane to plasma graft polymerization of an acrylic monomer and a crosslinkable monomer so that the pores of the microporous membrane are acrylic graft crosslinked. It is characterized by being filled with a polymer.

In a preferred embodiment, the polyethylene microporous membrane serving as the base material of the separation membrane has a weight average molecular weight of 5 × 10 5.
^A microporous membrane composed of ⁵ or more ultra high molecular weight polyethylene,
Thickness 0.1 to 50 μm, porosity 30 to 95%, average pore size 0.005 to
Use the one with 1 μm and breaking strength of 400 kg / cm ² or more.

Further, in the method of the present invention for separating an organic solvent mixture, the polyethylene microporous membrane is subjected to plasma graft polymerization using an acrylic monomer and a crosslinkable monomer so that the pores of the microporous membrane are acrylic graft-crosslinked. It is characterized in that an organic solvent having an affinity for an acrylic graft-crosslinked polymer is selectively separated by a pervaporation method or a reverse osmosis method using a separation membrane filled with a polymer.

The present invention will be described in detail below. First, the separation membrane of the present invention will be described.

The separation membrane of the present invention has a polyethylene microporous membrane as a base material. The polyethylene microporous membrane may be made of ultrahigh molecular weight polyethylene or a polyethylene composition containing ultrahigh molecular weight polyethylene, but from the viewpoint of strength and the like, it is preferable to use ultrahigh molecular weight polyethylene.

When a microporous membrane made of ultra-high molecular weight polyethylene is used as the base material of the separation membrane, the ultra-high molecular weight polyethylene used as the material is a homopolymer of ethylene or ethylene and 10 mol% or less of α-olefin. It is a crystalline linear ultra high molecular weight polyethylene composed of a copolymer. Its molecular weight is such that 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 ultrahigh molecular weight polyethylene affects the mechanical strength of the obtained separation membrane. If the weight average molecular weight is less than 5 × 10 ⁵ , an extremely thin separation membrane having high strength cannot be obtained. On the other hand, the upper limit of the weight average molecular weight is not particularly limited, but if the weight average molecular weight exceeds 1 × 10 ⁷ , it is difficult to form a thin film by stretching, which is not preferable.

As a material for the ultrahigh molecular weight polyethylene microporous membrane, in addition to the above materials, it is possible to use an ultrahigh molecular weight polyethylene blended with other relatively high molecular weight polyethylene. In this case, a polyethylene composition containing 1% by weight or more of ultrahigh molecular weight polyethylene having a weight average molecular weight of 7 × 10 ⁵ or more and having a weight average molecular weight / number average molecular weight of 10 to 300 is preferable.

The polyethylene composition has a weight average molecular weight / number average molecular weight of 10 to 300, preferably 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 becomes high during dissolution, so that it is difficult to prepare a high-concentration solution. Also
When it exceeds 300, the low molecular weight component is broken during stretching, and the strength of the entire film is reduced.

The weight average molecular weight / number average molecular weight is
It is used as a measure of the molecular weight distribution, and the larger the ratio of the molecular weights, the wider the width of the molecular weight distribution.
That is, in a composition composed of polyethylene having different weight average molecular weights, the larger the ratio of the molecular weights of the composition,
The difference in the weight average molecular weight of the blended polyethylene is large,
Further, the smaller the value, the smaller the difference in the weight average molecular weight.

In such a polyethylene composition,
The content of the ultra high molecular weight polyethylene is preferably 1% by weight or more, based on 100% by weight of the entire polyethylene composition as described above. Ultra high molecular weight polyethylene content is 1
If it is less than wt%, the entanglement of the molecular chains of the ultra-high molecular weight polyethylene that contributes to the improvement of the stretchability is hardly 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 becomes 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
Those of × 10 ⁴ or more are preferable. Weight average molecular weight is 1 x 10
^If polyethylene less than ⁴ is used, breakage easily occurs during stretching, and the desired microporous membrane cannot be obtained, which is not preferable. In particular, it is preferable to add polyethylene having a weight average molecular weight of 1 × 10 ⁵ or more and less than 7 × 10 ⁵ to the ultrahigh molecular weight polyethylene.

Examples of such polyethylene include the same kind as the above-mentioned ultra high molecular weight polyethylene.
High density polyethylene is particularly preferable.

The above ultrahigh-molecular-weight polyethylene microporous film, whether used alone or in the form of a composition, may optionally contain an antioxidant, an ultraviolet absorber, a lubricant,
Various additives such as anti-blocking agents, pigments, dyes, and inorganic fillers can be added within a range that does not impair the object of the present invention.

Next, a method for producing the ultrahigh molecular weight polyethylene microporous membrane will be described. First, in the case of a microporous membrane consisting of ultra-high molecular weight polyethylene alone, for example, Japanese Patent Laid-Open No.
It can be produced by the method described in No. 035.

Next, a microporous membrane made of a polyethylene composition obtained by blending ultrahigh molecular weight polyethylene with relatively high molecular weight polyethylene 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 performed with stirring at a temperature at which the polyethylene composition is completely dissolved in the solvent. The temperature varies depending on the polymer and solvent used, but is preferably in the range of 140 to 250 ° C. 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 this polyethylene composition is extruded from a die to be molded. As the die, a sheet die having a rectangular die shape is usually used, but a double cylindrical hollow die, an inflation die or the like can also be used. When using sheet dies, the die gap is usually 0.1 to 5 mm.
It is 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 cooled to form a gel. Cooling is preferably performed at a rate of 50 ° C./min or more up to at least the gelation temperature.

Next, the gel-like molded product is stretched. The stretching is carried out by heating the gel-like molded product and using a normal tenter method, a roll method, an inflation method, a rolling method, or a combination of these methods at a predetermined magnification, as described above. Two
Axial stretching is preferred, and simultaneous longitudinal or transverse 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 below the crystal melting point. For example, 90 to 140 ° C, more preferably 10
It is in the range of 0 to 130 ° C.

The thickness of the polyethylene microporous membrane as the base material of the separation 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 and it is difficult to put it to practical use. On the other hand, when it exceeds 50 μm, it is not preferable because it is too thick and the permeation performance is deteriorated.

The porosity of the microporous membrane is preferably 30 to 95%, more preferably 50 to 90%. Porosity is 30
If it is less than%, the permeability of the separation target is insufficient, while 95
If it exceeds%, the mechanical strength of the film becomes small and the practicality is poor.

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

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

In the separation membrane of the present invention, an acrylic monomer and a crosslinkable monomer are graft-crosslinked and polymerized at least on the inner surfaces of the pores of the polyethylene microporous membrane, and the acrylic graft-crosslinked polymer is substantially fine. It has a structure in which the holes are closed. Here, "graft-crosslinked polymerization" means that so-called graft copolymers (polymers in which a branched molecular chain is bonded to a long molecular chain) are further crosslinked and polymerized. Graft cross-linking polymerization using an acrylic monomer and a cross-linking monomer is carried out by a plasma graft polymerization method as described later.

As the acrylic monomer, acrylic acid,
Methacrylic acid, acrylic ester, acrylamide,
Acrylonitrile, methacrylic acid ester, etc. can be used and are appropriately selected depending on the substance to be separated.

The crosslinkable monomer has two or more double bonds in the molecule, and is itself polymerized to form a molecular chain and to provide a site for crosslinking with another molecular chain. .. As such a crosslinkable monomer,
Vinyl acrylate, vinyl methacrylate, divinylbenzene, vinyl butyl acrylate, etc. can be used. As the crosslinkable monomer, it is preferable to use an acrylic monomer, but other crosslinkable monomers can also be used. The crosslinkable monomer is appropriately set in consideration of the types of the separation target and the acrylic monomer.

The blending ratio of the acrylic monomer and the crosslinkable monomer in the graft cross-linking polymerization is appropriately adjusted depending on the monomer species used, the intended use of the separation membrane, and the type of the object to be separated. 2: 1 is recommended.

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, it is possible to separate a substance that does not show a great affinity for the homopolymer of the acrylic monomer or the copolymer of the acrylic monomer and the crosslinkable monomer. That is, if a third monomer having a high affinity for the separation target is introduced to form a copolymer in which the separation target exhibits a high affinity, some acrylic polymers may have a low affinity. It becomes separable.

When the (crosslinkable) copolymer using the third monomer is formed in the pores of the polyethylene microporous membrane, the solubility of the copolymer in the object to be separated is taken into consideration. It is preferable to determine the third monomer type and its blending amount.

When the separation membrane of a benzene / cyclohexane mixture is used, it is preferable to carry out graft polymerization using methyl acrylate as the acrylic monomer and vinyl acrylate or divinylbenzene as the crosslinkable monomer. Polymethyl acrylate-based polymers have an affinity for benzene and tend to swell when dissolved in benzene, but because deformation is suppressed by crosslinking with the polyethylene microporous membrane (in the graft polymerization part),
Dissolution and diffusion due to the plasticizing effect of cyclohexane having no affinity is suppressed. Therefore, only benzene will pass through the graft cross-linking polymerized portion formed in the pores, and the separation membrane will selectively permeate benzene from the benzene / cyclohexane mixture. In the pores,
Swelling of the polymethyl acrylate crosslinked polymer with benzene is suppressed, the entire film is hardly deformed, and the film strength is not reduced.

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

In the present invention, the graft cross-linked polymer is formed on the inner surface of the pores of the microporous membrane by the plasma graft polymerization method using the acrylic monomer and the cross-linking monomer. In the plasma graft polymerization method, a polyethylene microporous film is irradiated with plasma to generate radicals, and then an acrylic monomer and a crosslinkable monomer are brought into contact with the microporous film for 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 performing the graft polymerization using an acrylic monomer. As described above, by generating radicals and graft-polymerizing not on the acrylic monomer side to be graft-polymerized but on the microporous film as the base material, the acrylic monomer can be graft-crosslinked on the inner surfaces of the pores. Further, the homopolymer formed at that time is washed away with a solvent. The graft polymer is also formed on the surface of the polyethylene microporous membrane other than the inner surface of the pores, but since this affects the substantial permeability, it is desirable to minimize it.

FIG. 1 is a schematic cross-sectional view conceptually showing a process for producing a separation membrane of the present invention by plasma graft polymerizing an acrylic monomer and a crosslinkable monomer on a microporous polyethylene membrane 1. As shown in FIG. 1 (a), the polyethylene microporous membrane 1 has a large number of pores 2 penetrating the membrane.
Plasma graft polymerization is performed on the microporous membrane using an acrylic monomer and a crosslinkable monomer to form a graft crosslinked polymer on the surface thereof. The acrylic cross-linked polymer 3 obtained by the graft cross-linking polymerization is formed not only on the membrane surface portion 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 cross-linked polymer 3 is formed on one surface of the microporous membrane. Here, the graft cross-linked polymer 3 is formed even in a part of the inside of the pores.
Is blocked. The separation membrane of the present invention may have either of these structures.

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

Specifically, the plasma graft polymerization comprises the following steps. (a) In the presence of a gas such as argon, helium, nitrogen, or air at a pressure of 10 ^{-2 to} 10 mbar, a microporous membrane usually has a frequency of 10 to 30 MHz, an output of 1 to 1000 W, and a power of 1 to 1000 seconds. Plasma treatment is performed. (b) Plasma treatment is applied to an inorganic or organic solvent (acrylic monomer and crosslinkable monomer are dissolved or suspended in this solvent) containing 1 to 10% by volume of acrylic monomer and 0.01 to 2% by volume of crosslinkable monomer. Immerse the microporous membrane prepared in the above, while bubbling nitrogen gas, argon gas, etc.
The graft polymerization reaction is carried out at 0 ° C for 1 to 60 minutes. In this step, each monomer is crosslinked and polymerized. As the solvent, water, alcohol such as methanol, 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, it is possible to obtain a separation membrane in which the crosslinked acrylic graft polymer substantially blocks the pores of the microporous membrane.
Since the plasma graft polymerization occurs only on the surface of the polyethylene microporous membrane, it does not deteriorate 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 as the membrane base material are filled with the crosslinked acrylic graft-crosslinked polymer. The pore-blocked acrylic graft-crosslinked polymer selectively takes up a particular component of the organic solvent mixture and permeates it to the opposite side of the membrane. Since the polyethylene microporous membrane has a high porosity, the amount of substances that permeate (separate) the acrylic graft-crosslinked polymer in the pores also increases, and efficient separation can be achieved. Further, since the swelling of the acrylic graft polymer itself is suppressed by the cross-linking of the polyethylene microporous 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 pervaporation, the liquid mixture to be separated is supplied to the primary side across 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 by a separation membrane obtained by performing plasma graft polymerization on a polyethylene microporous membrane using methyl acrylate and vinyl acrylate, benzene is a gas or liquid on the secondary side. Is taken out as.

The applicable temperature range in the separation method of the present invention is usually 0 to 120 ° C, preferably 10 to 100 ° C. At temperatures above 120 ° C, the heat resistance of the polyethylene microporous membrane becomes insufficient, causing problems in maintaining the film shape. At temperatures below 0 ° C, the unit membrane area, film thickness, and permeation amount per hour are small. 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. If the pressure exceeds 200 kg / cm ² , it becomes difficult to maintain the shape of the ultrahigh molecular weight polyethylene microporous membrane.

Examples of the organic liquid mixture which can be separated with high selectivity by the method of the present invention include aromatic hydrocarbons such as benzene and toluene, chlorinated hydrocarbons, tetrahydrofuran, aliphatic alcohols, aliphatic hydrocarbons, acetone and the like. And a mixture of two or more of the 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. Mixtures with different solubility parameters (organic solvents) can be mentioned.

[0056]

The present invention will be described in more detail by the following specific examples. Example 1 An ultrahigh molecular weight polyethylene microporous 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 used. Plasma was irradiated using a plasma polymerization device (manufactured by Samco Co., Ltd.). 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% of methyl acrylate.
Then, it was immersed in a methanol aqueous solution (methanol: water = 10: 90) in which vinyl acrylate was 1 wt% for 15 minutes.
The temperature of the aqueous methanol solution during immersion was 30 ° C.

After the 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 graft polymerization amount was measured by the change from the initial membrane weight. The amount of polymerization was 2.07 mg / cm ² .

Chloroform / n-hexane (72 wt%: 28 wt%) by pervaporation using this separation membrane
The separation experiment of the mixed solution was performed. The permeation flux (Q) and the separation coefficient (α) at that time were determined with the supply liquid temperature set to 25 ° C. 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, using methyl acrylate and vinyl acrylate, plasma graft polymerization was performed on an ultrahigh molecular weight polyethylene microporous membrane to obtain a separation membrane.

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

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

A separation experiment was carried out by the reverse osmosis method 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 selectively permeate and separate.

As can be seen from the above, the separation membrane of the example shows higher separation performance than the conventional separation membrane in the separation of the organic liquid mixture such as chloroform / n-hexane by the permeation method.

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

[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 cross-linked polymer substantially occludes the pores of the microporous membrane, it is possible to use the pervaporation method or the reverse osmosis method for grafting. It is possible to separate an organic substance having affinity with a polymer with high selectivity.

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

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view conceptually showing the step of plasma graft polymerizing an acrylic monomer on a polyethylene microporous membrane, (a) showing a polyethylene microporous membrane, and (b-1) and (b-2). Indicates a polyethylene microporous membrane that has been graft-polymerized.

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

[Explanation of symbols]

 1 Polyethylene microporous membrane 2 Pore 3 Graft cross-linked polymer

Claims (2)

[Claims] 1. An organic solvent characterized in that a microporous polyethylene membrane is plasma-grafted with an acrylic monomer and a crosslinkable monomer so that the pores of the microporous membrane are filled with an acrylic graft-crosslinked polymer. Separation membrane for mixtures. 2. A polyethylene microporous membrane comprising a separation membrane obtained by performing plasma graft polymerization using an acrylic monomer and a crosslinkable monomer to fill the pores of the microporous membrane with an acrylic graft crosslinked polymer. A method for separating an organic solvent mixture, which comprises selectively separating an organic solvent having an affinity for an acrylic graft-crosslinked polymer by a pervaporation method or a reverse osmosis method.