JPH0398632A - Separation membrane and separation method - Google Patents

Abstract

PURPOSE:To selectively separate an organic solvent having affinity to an acrylic graft polymer by blocking up fine pores of a ultra high molecular weight polyethylene finely porous film with acrylic graft polymer. CONSTITUTION:Methylacrylate is plasma-polymerized on a finely porous membrane of a super high molecular weight polyethylene having 0.1-50mum thickness, 30-95% of porosity, 0.005-1mum of average pore size, at least 200kg/cm<2> of rupture strength, and at least 5X10<5> weight average molecular weight. The fine pores of the finely porous membrane are blocked up by the polymerization. Benzene is separated from an organic solvent mixture containing benzene and cyclohexane by a pervaporation method or a reverse osmosis method using the membrane.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a separation membrane and a separation method for organic solvent mixtures.
In particular, the present invention relates to a separation membrane that can be suitably used to separate organic solvents that have a high affinity for acrylic polymers from organic solvents that have a low affinity for acrylic polymers, and a separation method using the separation membrane.

[Prior art and problems to be solved by the invention] A membrane separation method that separates various mixtures using a membrane with pores is
It has become increasingly popular in recent years, and the technology is being applied in a variety of fields. In addition, the objects to be separated in membrane separation methods are not only solid-liquid mixtures, but also include liquid-liquid, gas-gas, and gas-liquid mixtures, and there is a growing interest in the development of separation membranes and separation technologies for various mixtures. There is.

Separation of organic solvents by membrane separation is one of the fields that is attracting attention, and it is used to treat mixtures that could not be separated by conventional simple methods (for example, mixtures with close boiling points that are difficult to separate by distillation, azeotropes). , mixtures containing heat-sensitive substances, etc.
It is being researched as a method to separate or concentrate. Pervaporation and reverse osmosis are suitable for membrane separation of organic solvent mixtures.

The separation accuracy and efficiency of membrane separation methods, including pervaporation and reverse immersion methods, depend on the performance of the membrane itself, so it is important to use membranes with excellent strength, durability, and separation selectivity. Various polymer membranes have been proposed so far.

For example, JP-A No. 50-98568 discloses a permeable membrane in which polymerizable monomers are grafted onto the inner surface of the pores of a polymer film having pores. This permeable membrane uses a high-molecular polymer film with pores such as polyethylene, which has excellent durability, heat resistance, and chemical resistance, as the base material, and a polymerizable monomer that has an affinity for the separation target is added to the pores. Graft polymerized on the inner surface. death. However, although this separation membrane is suitable for separating aqueous mixtures by reverse osmosis, its performance cannot be said to be sufficient for separating organic solvent mixtures such as benzene/cyclohexane mixtures.

Further, JP-A-52-122279 discloses a separation membrane made of an aliphatic olefin polymer containing acid groups derived from unsaturated carboxylic acids and the like. This separation membrane has an unsaturated carboxylic acid or the like polymerized on the surface of a membrane base material made of an aliphatic olefin polymer or the like through a crosslinking reaction by radical reaction, light irradiation, or electron beam irradiation. Is this separation membrane pervaporative? In particular, unsaturated compounds can be relatively easily separated from a mixture of organic solvents. However, in practical use, this membrane is used on a porous support, and its performance is still insufficient.

In order to obtain an excellent separation membrane, it is basically necessary to reductively increase the affinity with the compound to be separated.

However, if the entire separation membrane is made of a material that has an affinity for the target substance, the separation membrane will swell and high separation selectivity will not be obtained due to the plasticizing effect.

Furthermore, there is also the problem of a decrease in the mechanical strength and durability of the separation membrane.

Therefore, an object of the present invention is to provide a separation membrane that can separate a mixture of organic solvents such as a benzene/cyclo/xane mixture with high selectivity and has excellent strength and durability. be.

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

[Means for Solving the Problems] As a result of intensive research in view of the above objectives, the present inventors used a microporous membrane of ultra-high molecular weight polyethylene having a specific porosity and average pore diameter, and coated the surface of this membrane with acrylic. By plasma graft polymerizing monomers, a separation membrane whose pores are substantially blocked with an acrylic graft polymer will selectively permeate organic solvents that have an affinity for the acrylic graft polymer, and will also have good strength and durability. The present invention was completed by discovering that a separation membrane with excellent properties can be obtained.

That is, the separation membrane of the present invention used for separating organic solvent mixtures has a thickness of 0.1 to 50 μm, a porosity of 30 to 95%, and an average pore diameter of 0.005 to 1. J m, breaking strength 200
kg/crl or more, an acrylic monomer is plasma graft polymerized onto a microporous membrane made of ultra-high molecular weight polyethylene with a weight average molecular weight of 15XlO' or more, thereby substantially closing the pores of the microporous membrane with the acrylic graft polymer. It is characterized by what it did.

Further, the method of the present invention for separating an organic solvent mixture has a thickness of 0.1 to 50 μm, a porosity of 30 to 95%, and an average pore diameter of 0.1 to 50 μm.
005 ~ 1 μm, breaking strength 200 kg/cM
As described above, an acrylic monomer is plasma graft polymerized onto a microporous membrane made of ultra-high molecular weight polyethylene having a weight average molecular weight of 5 XIO' or more, thereby substantially closing the pores of the microporous membrane with the acrylic graft polymer. It is characterized by selectively separating organic solvents that have an affinity for acrylic graft polymers by a pervaporation method using a separation membrane.

The present invention will be explained in detail below.

First, the separation membrane of the present invention will be explained.

The separation membrane of the present invention is based on an ultra-high molecular weight polyethylene microporous membrane. The ultra-high molecular weight polyethylene used as the material is a crystalline linear ultra-high molecular weight polyethylene consisting of an ethylene homopolymer or a copolymer of ethylene and 10 mol% or less of α-olefin. The molecular weight is such that the weight average molecular weight is 5 x 105 or more, preferably l x
IO' to IXIO'. The weight average molecular weight of ultra-high molecular weight polyethylene influences the mechanical strength of the resulting membrane. If the weight average molecular weight is less than 5×10', an extremely 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, 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 the ultra-high molecular weight polyethylene microporous membrane, a mixture of ultra-high molecular weight polyethylene and other relatively low molecular weight polyethylene can be used. In this case, it contains 1% by weight or more of ultra-high molecular weight polyethylene with a weight average molecular weight of 7X10'JEJ, and the weight average molecular weight is 7X10' JEJ. ! It is preferable to use a polyethylene knit sole having an i/number average molecular weight of 10 to 300.

The weight average molecular weight/number average molecular weight of the polyethylene composition is 10 to 300, preferably 12 to 250.

When the weight average molecular weight/number average molecular weight is less than 10, the average molecular length is large and the density of entanglement of molecular chains during dissolution becomes high, making it difficult to prepare a highly concentrated solution. Also 3
If it exceeds 00, some low molecular weight particles will break during stretching, resulting in a decrease in the strength of the entire film.

Note that the weight average molecular weight/number average molecular weight is used as a measure of molecular weight distribution, and the larger the ratio of this molecular weight, the wider the width of the molecular weight distribution. In other words, in a composition composed of polyethylenes having different weight average molecular weights, the larger the ratio of the molecular weights of the compositions, the greater the difference in the weight average molecular weights of the blended polyethylenes, and the smaller the ratio, the smaller the difference in weight average molecular weights. It shows.

The content of this ultra-high molecular weight polyethylene in the polyethylene composite sole is 1% by weight or more, with the entire polyethylene composite being 100% by weight. If the content of ultra-high molecular weight polyethylene is less than 1% by weight, the entanglement of the molecular chains of ultra-high molecular weight polyethylene, which contributes to improved stretchability, is hardly formed, making it impossible to obtain a high-strength microporous membrane. On the other hand, although the upper limit is not particularly limited, if it exceeds 90% by weight, it becomes difficult to achieve the desired high concentration of the polyethylene solution.

In addition, polyethylene other than ultra-high molecular weight polyethylene in the polyethylene composite has a weight average molecular weight of 7X105
However, the lower limit of molecular weight is I
' The above is preferred. Weight average molecular weight is I
If polyethylene having a molecular weight of less than O' is used, it is not preferable because breakage tends to occur during stretching and the desired microporous membrane cannot be obtained. Especially if the weight average molecular weight is I XIO' or more 7
It is preferable to blend less than XIO' polyethylene into the ultra-high molecular weight polyethylene.

Examples of such polyethylene include those similar to the above-mentioned ultra-high molecular weight polyethylene, but high-density polyethylene is particularly preferred.

In addition, the above-mentioned ultra-high molecular weight polyethylene microporous membrane may contain antioxidants, ultraviolet absorbers, lubricants, anti-blocking agents, pigments, dyes, Various additives such as inorganic fillers can be added within the range that does not impair the purpose of the present invention.

Next, a method for producing an ultra-high molecular weight polyethylene microporous membrane will be explained.

First, in the case of a microporous membrane made solely of ultra-high molecular weight polyethylene, it can be produced, for example, by the method described in JP-A-60-242035.

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

First, a highly concentrated solution is prepared by heating and dissolving the above-mentioned polyethylene composition in a solvent. This solvent is not particularly limited as long as it can sufficiently dissolve the polyethylene composite, and may be the same as those described in JP-A-60-242035. The heating and dissolving is performed while stirring at a temperature at which the polyethylene composite is completely dissolved in the solvent.

The temperature varies depending on the polymer and solvent used, but 1
The temperature range is preferably from 40 to 250°C. The concentration of the polyethylene composition solution is 10 to 50% by weight, preferably 1% by weight.
It is 0 to 40% by weight.

Next, the heated solution of this polyethylene composition is extruded through a die to form a mold. As the die, a sheet die with a rectangular base shape is usually used, but a double cylindrical hollow die, an inflation die, etc. can also be used. The die gap when using a sheet die is usually 0.1 to 5m+n, and when extrusion forming, it is 140 to
Heated to 250°C.

At this time, the extrusion speed is usually 20 to 30 cm/min to 2.
~3m. /minute.

The solution extruded from the die in this way is shaped into a gel by cooling. Cooling is preferably carried out at a rate of 50° C./min or more until at least the temperature is below the gelling temperature.

Next, this gel-like shape is stretched. Stretching is carried out by heating the gel-like shape and using the usual tenter method, roll method, inflation method, rolling method, or a combination of these methods at a predetermined magnification in the same manner as described above. Biaxial stretching is preferred, and simultaneous stretching in the longitudinal and lateral directions or sequential stretching may be used, but simultaneous biaxial stretching is particularly preferred.

The stretching temperature is below the melting point of the polyethylene composite + 10°C,
The range is preferably from the crystal dispersion temperature to below the crystal melting point. For example, 90-140°C, more preferably 100°C
~130°C.

The thickness of the ultra-high molecular weight polyethylene microporous membrane, which is the base material of the separation membrane of the present invention obtained in this way, is 0.1 to 50.
μm1 is preferably 0.2 to 25 μm.

If the thickness is less than 0.1 μm, the mechanical strength of the film is low and it is difficult to put it into practical use. On the other hand, if it exceeds 50 μm, it is too thick and reduces transmission performance, which is not preferable.

The porosity of the microporous membrane is 30-95%, preferably 50-9
The range is 0%. If the porosity is less than 30%, the permeability of the object to be separated will be insufficient, while if it exceeds 95%, the mechanical strength of the membrane will be low, making it impractical.

The average pore diameter is 0. It is within the range of 0.005 to 1 μm. Average pore size is 0. If the average pore diameter is less than 0.005 μm, the permeability of the target substance to be separated will be insufficient, and if the average pore diameter exceeds 1 μm, the separation performance will deteriorate.

Further, by setting the breaking strength to 200 kg l cd or more, the acrylate graft polymer has sufficient deformation resistance against swelling when a solvent is dissolved.

In the separation membrane of the present invention, an acrylic monomer is graft-polymerized on at least the inner surface of the microporous membrane of the ultra-high molecular weight polyethylene microporous membrane described above, and the membrane has a structure in which the acrylic polymer substantially closes the pores. Graft polymerization of acrylmo/mer is carried out by a plasma graft polymerization method as described below.

Acrylic acid, notacrylic acid, and esters thereof can be used as the acrylic monomer, and are appropriately selected depending on the object to be separated.

When preparing a separation membrane for a benzene/cyclohexane mixture, methyl acrylate is graft-polymerized. Polymethyl acrylate has an affinity for benzene and tends to swell when benzene dissolves, but the ultra-high molecular weight polyethylene microporous membrane suppresses deformation, making it possible to plasticize cyclohexane, which has no affinity. The effect of dissolution and diffusion is suppressed. Therefore, only benzene will pass through the pores, and the separation membrane will selectively permeate benzene from the benzene/cyclohexane mixture. In addition, within the pores, the swelling of polymethyl acrylate due to benzene is suppressed, and the entire membrane is hardly deformed.
No decrease in membrane strength occurs.

A plasma graft polymerization method is used to graft-polymerize the acrylic monomer onto the inner surface of the pores of the microporous membrane. In the plasma graft polymerization method, a microporous membrane made of ultra-high molecular weight polyethylene is irradiated with plasma to generate radicals, and then an acrylic monomer is brought into contact with the microporous membrane and graft polymerized. Plasma graft polymerization includes gas phase polymerization and liquid phase polymerization, and liquid phase polymerization is preferred for graft polymerizing acrylic monomers. By generating radicals in the microporous membrane serving as the base material and performing graft polymerization instead of using the acrylic monomer to be graft-polymerized in this manner, the acrylic monomer can be graft-polymerized to the inner surface of the pores. In addition, the homobolimer that has grown at that time is washed away with a solvent. Although the graft polymer is present on surfaces other than the inner surface of the pores of the ultra-high molecular weight polyethylene microporous membrane, it is desirable to minimize the amount since this affects the substantial permeability.

Figure 1 (a), (b-1) and (b-2) l! ,
1 is a cross-sectional view conceptually showing a process of plasma graft polymerizing an acrylic monomer onto an ultra-high molecular weight polyethylene microporous membrane 1 to obtain a separation membrane of the present invention. The ultra-high molecular weight polyethylene microporous membrane 1 has a large number of pores 2 penetrating the membrane. Plasma graft polymerization is performed on this microporous membrane to graft polymerize an acrylic monomer onto its surface. The graft-polymerized acrylic polymer 3 is formed not only on the surface of the microporous membrane but also on the inner surface of the tag. (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 polymer 3 is formed on one surface of the microporous membrane. Here, the graft polymer 3 is formed into a portion of the pore and closes the pore 2. The separation membrane of the present invention may have either of these structures.

The homopolymer produced as a by-product during the plasma graft polymerization process is completely washed away using a solvent such as toluene, and only the graft polymer is placed on the surface of the ultra-high molecular weight polyethylene microporous membrane (inner pore surface and membrane surface). leave it in

Specifically, plasma graft polymerization consists of the following steps.

(a) a lualcon with a pressure of 10-2 to 10 mbar;
In the presence of gases such as helium, nitrogen, air, etc., the normal frequency is 10~30MHz, the output is 1~1000, and the frequency is 1~10.
00 seconds of plasma treatment is performed on the microporous membrane.

(b) Plasma-treated microporous membrane of 1 to IO wt%
acrylic monomer dissolved or suspended in an inorganic or organic solvent, especially an aqueous solution, and heated to 20 to 100 °C while bubbling nitrogen gas, argon gas, etc.
Then, the graft polymerization reaction is carried out for 1 to 60 minutes.

(C) The obtained microporous membrane is washed with toluene, xylene, etc. for about 1 hour and dried.

By the plasma graft polymerization method described above, it is possible to obtain the desired separation membrane in which the pores of the microporous membrane are substantially blocked with the acrylic graft polymer.

Since plasma graft polymerization occurs only on the surface of the ultra-high molecular weight polyethylene microporous membrane, it does not deteriorate the membrane base material. Furthermore, since the graft polymer is chemically bonded to the membrane base material, it does not change over time.

In the separation membrane of the present invention, it is necessary that the acrylic graft polymer substantially closes the pores of the ultra-high molecular weight polyethylene microporous membrane that is the membrane base material. The acrylic graft polymer blocking the pores selectively takes up a certain portion of the organic solvent mixture and allows it to pass through to the other side of the membrane.

Because the porosity of the ultra-high molecular double polyester microporous membrane is high,
The amount of substances that permeate (separate) the acrylic graft polymer in the pores also increases, allowing efficient separation. Furthermore, since the ultra-high molecular weight polyethylene microporous membrane suppresses swelling of the acrylic graft polymer, the strength of the membrane as a whole does not decrease.

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

In the method of the present invention, an organic solvent mixture is separated by a pervaporation method or a reverse osmosis method using the separation membrane of the present invention described in detail so far.

The pervaporation method or reverse osmosis method in the method of the present invention is basically the same as the known pervaporation method or reverse osmosis method except that the separation membrane of the present invention is used. The mixed liquid to be separated is supplied to the primary side across the two sides, the secondary side is set as the low pressure side, and a portion of the mixed liquid is taken out as gas or liquid to the secondary side.

When a benzene/cyclohexane mixture, for example, is separated using a microporous ultra-high molecular weight polyethylene membrane graft-polymerized with methyl acrylate as a separation membrane, benzene is taken out as a gas or liquid on the secondary side.

The applicable temperature range in the separation method of the present invention is usually 0 to 120
°C, preferably 10 -1 (10 °C.12
f) At temperatures above 0°C, the heat resistance of the high molecular weight polyethylene microporous membrane becomes insufficient, causing problems in maintaining the membrane shape, and at temperatures below 0°C, the permeation rate per unit membrane area, membrane thickness, and time decreases. I don't like it because it's getting smaller.

Moreover, the pressure range applicable to the separation method of the present invention is 200
kg/cd or less, preferably 100 kg/cf
It is below fl. At pressures exceeding 200 kg/crl, it becomes difficult to maintain the shape of the microporous ultra-high molecular weight polyethylene membrane.

The organic liquid mixture that can be separated by the method of the present invention includes benzene, which is a solvent that dissolves polyacrylic acid ester;
Toluene, chlorinated hydrocarbons, tetrahydrofuran, aliphatic alcohols with 1 to 4 carbon atoms, and aliphatic hydrocarbons that do not dissolve polyacrylic esters, carbon tetrachloride, aliphatic alcohols (with 5 carbon atoms), etc. above>, cyclohexanol, tetrahydrofurfural, etc. In addition to the above-mentioned benzene/cyclohexane, benzene/n-hexane, benzene/n-heptane, toluene/cyclohexane, toluene/methylcyclohexane, hexane /heptane, toluene/benzene, benzene/water, etc. These mixtures are not limited to the two-part system as described above, but may also be a multi-part system of three or more parts.

〔Example〕

The present invention will be explained in more detail by the following specific examples.

Example 1 Weight average molecular weight 25 x 10', film thickness 10 μm, porosity 70%, average pore diameter 0.02 μm, breaking strength 4700 k
A microporous membrane of ultra-high molecular weight polyethylene (manufactured by Tonen Petrochemicals Ltd.) of g/cm was irradiated with plasma using a plasma polymerization device (manufactured by Samco Ltd.).The plasma treatment conditions at this time are shown in Table (2).

Next, the plasma-treated ultra-high molecular weight polyethylene microporous membrane was added to a 4% by volume methyl acrylate aqueous solution for 15 minutes.
Soaked for minutes. Note that the temperature of the aqueous solution during immersion was 30°C.

After soaking, the ultra-high molecular weight polyethylene microporous membrane was washed in toluene day and night and dried at room temperature. After drying, the weight of the membrane was measured, and the amount of graft polymerization was determined by the change from the initial membrane weight. The amount of polymerization was 2.3 μ/ctl.

The ATR of the obtained membrane was measured and the material formed on the ultra-high molecular weight polyethylene microporous membrane was found to be polymethinorea acrylate.
I was very sure that it was 1.

Using this separation membrane, an experiment was conducted to separate a benzene/cyclohexane mixed solution by pervaporation. When the temperature of the feed liquid (benzene/cyclohexane mixed solution: benzene concentration (weight ratio > 0.5) is 25°C, 40°C, 50°C, and 60°C, the permeate flow (Q) and separation coefficient α> The results are shown in Figure 2.

Example 2 In the same manner as in Example 1, a separation membrane was formed by graft polymerizing methyl acrylate onto an ultra-high molecular weight polyethylene microporous membrane.

Separation experiments were conducted using the pervaporation method with the temperature of the feed solution (benzene/cyclohexane mixed solution) set at 50°C and the concentration (weight ratio) of benzene in the mixed solution between 0.2 and 0.9. . The weight ratio of benzene in the gas that passed through the separation membrane was determined. The results are shown in Figure 3. Also, the permeation flux (Q) and separation coefficient (α>) at this time were determined.

The results are shown in Figure 4.

As can be seen from the above, the separation membrane of the present invention selectively permeates benzene from a benzene/cyclosexane mixed solution over a wide concentration and temperature range. In particular, when the temperature of the feed liquid is 25°C, the separation coefficient shows an extremely high value of 14.8.

〔Effect of the invention〕

The separation membrane of the present invention uses an ultra-high molecular weight polyethylene microporous membrane as a base material, has good swelling resistance in organic solvents, and has excellent mechanical strength and durability.

In addition, in the separation membrane of the present invention, the acrylic polymer substantially blocks the pores of the microporous membrane, so by using the pervaporation method or reverse osmosis method, the acrylic polymer has an affinity with the graft polymer. Certain organic substances can be separated with high selectivity. In particular, when a separation membrane graft-polymerized with methyl acrylate monomer is used, solvents that dissolve polyacrylic acid such as benzene, toluene, chlorinated hydrocarbons, and tetrahydrofuran, and polyacrylic acids such as aliphatic hydrocarbons and carbon tetrachloride can be dissolved. The solvent can be selectively decomposed from a mixed solution with a non-solvent, and in particular, benzene can be selectively separated from a benzene/cyclohexane mixed solution.

The separation membrane of the present invention is preferable because it uses a microporous membrane of ultra-high molecular weight polyethylene as a base material, so that a uniform and reproducible separation membrane can be easily obtained.

Such a separation membrane is suitably used for the separation of organic solvent mixtures by barbage separation or reverse osmosis, and is particularly useful for the separation of benzene/cyclohexane mixtures.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view conceptually showing the process of plasma graft polymerization of an acrylic monomer onto a microporous ultra-high molecular weight polyethylene membrane; (a) shows the microporous ultra-high molecular weight polyethylene membrane; (b-1) and (b-2) respectively show graft-polymerized ultra-high molecular weight polyethylene microporous membranes, and Fig. 2 shows a benzene/cyclohexane mixed solution by Barbay separation method using a separation membrane according to an embodiment of the present invention. FIG. 3 is a graph showing the relationship between the temperature of the benzene/cyclohexane mixed solution, permeation flux (Q), and separation coefficient (α) when benzene is separated from the benzene/cyclohexane mixed solution to be separated. 4 is a graph showing the relationship between the concentration of benzene in the substance and the weight ratio of benzene in the substance that has permeated through the separation membrane. It is a graph showing the relationship between east (Q) and separation coefficient (α). 3. Graft polymer applicant: Tonen Petrochemical Co., Ltd. Representative: Patent attorney Tachibana Takaishi
Horse l...Ultra high molecular weight polyethylene microporous membrane 2...
Pore Inertia Diagram 2 Temperature (0C) Figure 3 Figure 4

Claims (4)

[Claims] (1) Thickness 0.1-50 μm, porosity 30-95%, average pore diameter 0.005-1 μm, breaking strength 200 kg/cm
Acrylic monomer is plasma graft polymerized onto a microporous membrane made of ultra-high molecular weight polyethylene with a weight average molecular weight of 5 x 10^5 or more, and the pores of the microporous membrane are substantially filled with the acrylic graft polymer. A separation membrane for organic solvent mixtures, characterized in that it is clogged with . (2) The separation membrane for organic solvent mixtures according to claim 1, wherein the graft polymer that blocks the pores is polymethyl acrylate. (3) Thickness 0.1-50 μm, porosity 30-95%, average pore diameter 0.005-1 μm, breaking strength 200 kg/cm
Acrylic monomer is plasma graft polymerized onto a microporous membrane made of ultra-high molecular weight polyethylene with a weight average molecular weight of 5 x 10^5 or more, and the pores of the microporous membrane are substantially filled with the acrylic graft polymer. 1. A method for separating an organic solvent mixture, comprising selectively separating an organic solvent having an affinity for an acrylic graft polymer by a pervaporation method or a reverse osmosis method using a separation membrane formed by clogging the acrylic solvent. (4) In the method according to claim 3, the graft polymer that blocks the pores is polymethyl acrylate;
A method for separating an organic solvent mixture, comprising separating benzene from an organic solvent mixture containing benzene and synchlohexane.