JPH11106593A - Polyisopropenyl acetate separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a separation membrane which exhibits high permeation rate and separation coefficient in separating a mixture of water/an org. substance and a high water permeation rate by forming the membrane from a polyisopropenyl acetate copolymer formed from isopropenyl acetate and a vinyl monomer copolymerizable therewith. SOLUTION: A polyisopropepnyl acetate copolymer obtd. by copolymerizing isopropenyl acetate with a vinyl monomer copolymerizable therewith is used for preparing a separation membrane with a thickness of 500-0.5 μm by known techniques. The membrane is saponified if necessary, giving the objective separation membrane which comprises a polyisopropenyl acetate copolymer subsbtantially comprising repeating units represented by the formula (wherein A is a residue of a vinyl monomer copolymerizable with isopropenyl acetate; and m, n, x, and y are each mol.%, and m is 100-1, m+n is 100, x is 100-0, and x+y is 100).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyisopropenyl acetate-based separation membrane. More specifically, the present invention relates to a highly hydrophilic separation membrane comprising a saponified product of a copolymer of isopropenyl acetate and a vinyl compound.

[0002]

2. Description of the Related Art Hitherto, polymethyl methacrylate, polyvinyl acetate and copolymers thereof have been well known as paints, adhesives and medical materials. Polymethyl methacrylate has extremely high transparency and excellent gas permeability,
Further, since polymers having a vinyl alcohol residue, which is a saponified product of polyvinyl acetate and a copolymer thereof, have an advantage of high hydrophilicity, development of separation membranes using these materials has been actively conducted.

Concentration / separation of an aqueous solution of an organic substance using a membrane A reverse osmosis method has been put to practical use for the concentration of a part of an aqueous solution of an organic substance having a low concentration. However, the reverse osmosis method needs to apply a pressure equal to or higher than the osmotic pressure of the separation liquid to the liquid to be separated, and therefore cannot be applied to a highly concentrated aqueous solution in which the osmotic pressure is high. There is a limit.

On the other hand, pervaporation and vapor permeation methods which are not affected by osmotic pressure are attracting attention as new separation methods. In the pervaporation method, a separation liquid is supplied to the primary side of a membrane and the secondary side (permeation side) of the membrane is depressurized or a carrier gas is passed to allow the separation substance to pass through the membrane in a gaseous state. Is the way. The vapor permeation method is different from the permeation vaporization method in that the supply to the primary side of the membrane is a mixed vapor. The membrane permeable substance is
It can be collected by cooling and condensing the permeated vapor. Many studies have been reported on the pervaporation method. For example, U.S. Pat. No. 3,035,060 discloses water / polyvinyl alcohol crosslinked with maleic acid.
A pervaporation membrane of an alcohol mixture is disclosed.

On the other hand, Japanese Patent Publication No. 58-19681 discloses one or more alkyl acetate-substituted vinyl and alkylene acetate, one or more alkyl vinyl ether and aliphatic vinyl ester, and vinyl acetate. And a method for producing a modified polyvinyl alcohol obtained by saponifying the copolymer.
No. 8 discloses a water-soluble film which is a completely saponified product of a vinyl acetate-isopropenyl acetate copolymer, and JP-A No. 62-46644 discloses an isopropenyl acetate-ethylene-vinyl acetate copolymer. Laminates of the unified saponified product with another thermoplastic resin are described. However, none of the above-mentioned prior art documents discloses a separation membrane.

[0006]

When the above-mentioned polymethyl methacrylate or polyvinyl acetate is used as a separation membrane such as a water-selective pervaporation membrane, a vapor permeable membrane, and an ultrafiltration membrane, the permeation flux of water is increased. Therefore, it is necessary to impart further hydrophilicity to the membrane. For example, when water-soluble polyvinyl alcohol is used as a film material, not only problems remain in thermal stability and mechanical strength, but also chemical cross-linking for insolubilizing polyvinyl alcohol is required, which complicates the film forming process. . Further, from the viewpoint of practical use, it is necessary to make the membrane structure porous so as to increase the throughput, but it is difficult to make the above-mentioned polyvinyl alcohol into a porous membrane because the solidification rate of the polymer is extremely slow.

[0007]

Means for Solving the Problems The present inventors formed a separation membrane using a specific polyisopropenyl acetate-based copolymer to maintain hydrophilicity while maintaining mechanical and chemical strength. It was thought that it would be possible to increase the porosity and that it could be made porous by a phase inversion method, like polymethyl methacrylate. As a result, the present inventors have found that a copolymer membrane of isopropenyl acetate and a vinyl monomer copolymerizable therewith, preferably methyl methacrylate or vinyl acetate, and a saponified product thereof are useful separation membranes. Thus, the present invention has been completed.

That is, the present invention is a separation membrane comprising a polyisopropenyl acetate copolymer substantially consisting of a repeating unit represented by the general formula (I).

[0009]

Embedded image

(Where A represents a vinyl monomer residue copolymerizable with isopropenyl acetate, m and n, x and y each represent mol%, and each m = 10
0-1 and n = 100-m, x = 100-0 and y = 100-x)

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As a method for producing a polyisopropenyl acetate copolymer used in the present invention, for example, isopropenyl acetate and a vinyl monomer copolymerizable therewith are mixed with 2,2 ′ in an organic solvent. -A method of radical copolymerization using an initiator such as azobisisobutyronitrile (hereinafter abbreviated as AIBN), a method of photoemulsion polymerization in the presence of a surfactant, and the like.

In the present invention, vinyl monomers copolymerizable with isopropenyl acetate include vinyl acetate, vinyl propionate, vinyl decanoate, vinyl pivalate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, acrylic Examples thereof include methyl acrylate and ethyl acrylate, and particularly preferred are vinyl acetate, methyl methacrylate, and vinyl pivalate.

The reaction temperature in the polymerization of isopropenyl acetate with a vinyl monomer varies depending on the type of the reaction raw materials, the type of the polymerization reaction and the like.
C., preferably in the range of 0 to 40.degree. The time required for the polymerization reaction varies greatly depending on the type of the reaction raw material components, the type of the polymerization reaction, the reaction temperature, etc., but is usually in the range of 2 hours to 60 days, preferably in the range of 2 days to 30 days. Will be implemented. In the present invention, it is preferable that oxygen is not present as a reaction atmosphere at the time of carrying out the reaction, and it is preferable that the reaction is carried out in a reduced-pressure sealed state. Further, the polymerization reaction is usually stopped by cooling the reaction product. In the separation and purification of the polymer after the completion of the polymerization reaction, known methods can be applied. For example, the target polymer can be precipitated by dropping the mixture after the reaction to the polymer non-solvent or adding the polymer non-solvent to the polymer solution. Methanol, ethanol, isopropanol, petroleum ether and the like can be exemplified as those usually used as a non-solvent for the polymer. These may be used alone or as a mixture of two or more.

The molecular weight of the copolymer depends on the proportion of isopropenyl acetate in the polymer, but the molecular weight of isopropenyl acetate / methyl methacrylate is 5%.
× 10 ^{3 to} 5 × 10 ⁵ , and 1 × 10 ³ to 2 × 10 ⁵ for isopropenyl acetate / vinyl acetate copolymer. In addition, intrinsic viscosity (η) of 10 g / l (1 W / V%) measured in benzene at 30 ° C
Is 0.07 to 0.30 dl / g for an isopropenyl acetate / methyl methacrylate copolymer and 0.58 to 4.3 dl / g for an isopropenyl acetate / vinyl acetate copolymer.
Isopropenyl acetate / methyl methacrylate copolymer and isopropenyl acetate / vinyl acetate copolymer are both dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), tetrahydrofuran (THF),
It is soluble in organic solvents such as benzene, hexane, acetone and dichloromethane.

The ratio of the isopropenyl acetate residue in the polyisopropenyl-based separation membrane consisting essentially of a copolymer of isopropenyl acetate and a vinyl monomer according to the present invention may be in the range of 100 to 1 mol%. However, in consideration of a range that does not become water-soluble when hydrophilizing by saponification, a range of 50 to 1 mol% is preferable.

The polyisopropenyl-based separation membrane of the present invention comprises:
By saponification, the membrane becomes hydrophilic and becomes a membrane suitable for aqueous separation. As a method for saponifying a polyisopropenyl-based copolymer, an aqueous solution of an alkali such as potassium hydroxide or sodium hydroxide or an aqueous solution of an alcoholic alkali such as methanol or ethanol is added dropwise, or a polyisopropenyl-based separation film formed in advance is used. For example, saponification is performed by immersing the film in the alkaline solution. The degree of saponification depends on the content of the isopropenyl acetate component, but is not particularly limited as long as the content does not become water-soluble, and the content of the isopropenyl acetate component is reduced.
Complete saponification is preferred in the range of 50 to 1 mol%.

The method for producing the separation membrane of the present invention is not particularly limited, and any of a uniform membrane such as a flat membrane, a tubular membrane, a hollow fiber membrane and the like and an asymmetric membrane (non-uniform membrane) may be used according to a conventionally known technique. But it is possible. The thickness of the separation membrane is 500 to 0.5 μm, preferably 200 to 1 μm, more preferably 100 to 10 μm, in consideration of both the large asymmetric film and the small thin film. In addition, by applying a composite film on a porous support, the film thickness can be reduced to about 0.1 μm. The membranes thus produced are prepared from various organic mixtures, more preferably water / organic mixtures, for example organic acids such as formic acid, acetic acid, propionic acid, butyric acid, methanol, ethanol, 1-propanol,
One or more compounds selected from the group consisting of alcohols such as 2-propanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, aldehydes such as acetaldehyde and propionaldehyde, and amines such as pyridine and picoline. Used for separation of an aqueous solution or a vapor mixture with water. Further, application to reverse osmosis, ultrafiltration, gas separation and the like is also possible.

[0018]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Here, the specific permeation rate in the pervaporation method and the vapor permeation method is a value obtained by multiplying the permeation mixture amount per unit membrane area by the film thickness, and is expressed in units of kg · m ⁻¹ · h ^−1. The separation coefficient (α) is a value of the ratio of the component 1 and the component 2 in the permeated gas to the ratio of the component 1 and the component 2 in the supply liquid or the supply vapor. That is, α = (X / Y) p / (X / Y) f. X and Y represent the respective compositions (% by weight) of the components 1 and 2 in the two-component system, and p and f represent the permeate side and the supply side, respectively.

The permeation rate of pure water in an ultrafiltration membrane is the permeation rate of water per unit membrane area when water is used as a feed liquid, and is expressed in units of kg · m ^-2 · h ⁻¹ , Is the percentage of protein that does not permeate the membrane, and R =
1- (Cp / Cb). Cb represents the protein concentration in the feed solution, and Cp represents the protein concentration in the permeate.

Method for Preparing Isopropenyl Acetate Copolymer Isopropenyl acetate (hereinafter i-P
Ac, abbreviated as Wako Pure Chemical Industries, Ltd., reagent grade, methyl methacrylate (abbreviated as MMA, Wako Pure Chemical Industries, Ltd., reagent grade) and vinyl acetate (abbreviated as VAc, Wako Pure Chemical Industries) (Special grade, manufactured by Co., Ltd.) was washed three times with a saturated aqueous solution of sodium hydrogen sulfite and water, dehydrated with calcium chloride, and distilled under reduced pressure twice under a nitrogen atmosphere. An isopropenyl acetate / methyl methacrylate copolymer (hereinafter abbreviated as i-PAc-MMA) is prepared by charging each monomer at a ratio of 1: 1 (volume ratio), using AIBN as an initiator, at 40 ° C. in a dimethyl sulfoxide solution. And radical polymerization.

Further, isopropenyl acetate / vinyl acetate copolymer (hereinafter abbreviated as i-PAc-VAc) is i-Pac-VAc.
It was prepared in the same manner as under Ac-MMA under the same conditions.

The obtained i-PAc-MMA and i-PAc-
VAc was precipitated with methanol, acetone /
It was reprecipitated with water and dried at 25 ° C. under reduced pressure.

Example 1 An 8% by weight N, N-dimethylformamide (hereinafter abbreviated as DMF) solution of i-PAc-MMA (molecular weight 3.3 × 10 ⁵ ) containing 5 mol% of an i-PAc component was placed on a glass plate. Cast and 80
C. for 12 hours to obtain a transparent film-like film.
The thickness of the obtained film was 57 μm. A batch type membrane separator (volume: 200 ml, effective membrane area: 15 cm ² ) was used for the pervaporation experiment of the obtained membrane. Water / ethanol mixture (ethanol concentration 95% by weight) was used as the supply liquid.
The test was performed at 25 ° C. and a pressure of 1333 Pa on the permeation side. Table 1 shows the measurement results of the specific transmission speed and the separation coefficient.

Example 2 i-PAc-VAc containing 50 mol% of i-PAc component
An 8% by weight DMF solution (molecular weight: 2 × 10 ⁵ ) was cast on a glass plate and dried at 80 ° C. for 12 hours to obtain a transparent film. The thickness of the obtained film was 59 μm. The pervaporation experiment of the obtained membrane was performed under the same conditions as in Example 1 except that a water / 2-propanol mixed solution (2-propanol concentration: 5% by weight) was used as a supply liquid. Table 1 shows the measurement results of the specific transmission speed and the separation coefficient.

Example 3 The i-PAc-MMA film-like film obtained in Example 1 was immersed in a 1N aqueous solution of potassium hydroxide at 60 ° C. for 1 hour for saponification. Saponification progressed 100%. A pervaporation experiment of the obtained membrane was performed under the same conditions as in Example 1 using a water / ethanol mixture (ethanol concentration 95% by weight). Table 1 shows the measurement results of the specific transmission speed and the separation coefficient.

Example 4 An 8 wt% DMF solution of i-PAc-MMA used in Example 1 was cast on a glass plate and dried at 80 ° C. for 5 minutes.
Gelation was performed in water at 25 ° C.

The thickness of the obtained film was 197 μm. The measurement of the pure water permeation rate and the ultrafiltration experiment of the obtained membrane were performed using a batch type membrane separator (volume: 200 ml, effective membrane area: 28.7 cm ² ) at a feed liquid temperature of 25 ° C. and an operating pressure of 0.2 to 1.0 kg /. The test was performed under the condition of cm ² . The solute used in the ultrafiltration experiment was bovine serum albumin (Sigma, molecular weight 80,000) at a concentration of 100 mg / l. FIG. 1 shows the relationship between the pure water permeation rate and the operating pressure. The inhibition rate of bovine serum albumin in the ultrafiltration experiment was 40%.

Comparative Example 1 Polymethyl methacrylate (hereinafter abbreviated as PMMA, Polymer)
Using a 15% by weight DMF solution (manufactured by Scientific Products), a transparent film-like film was produced in the same manner as in Example 1.
The thickness of the obtained film was 56 μm. The pervaporation experiment of the obtained membrane was performed using a water / ethanol mixture (ethanol concentration 95
% By weight) under the same conditions as in Example 1.
Table 1 shows the measurement results of the specific transmission speed and the separation coefficient.

Comparative Example 2 A 15% by weight DMF solution of PMMA used in Comparative Example 1 was cast on a glass plate in the same manner as in Example 1, dried at 80 ° C. for 5 minutes, and then in water at 25 ° C. Gelation was performed. The thickness of the obtained film was 267 μm. The measurement of pure water permeation rate and the ultrafiltration experiment of the obtained membrane were performed in the same manner as in Example 4. FIG. 1 shows the relationship between the pure water permeation rate and the operating pressure. Bovine serum albumin inhibition rate in ultrafiltration experiments is 70%
Met.

[0031]

[Table 1]

[0032]

As is clear from Table 1, the polyisopropenyl-based separation membrane according to the present invention has a higher permeation rate and a higher separation coefficient for separation of a water / organic mixture than a general-purpose polymer membrane. In addition, the water permeation rate is high in ultrafiltration, which is extremely effective for practical use of a membrane separation process.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a pure water permeation rate and an operation pressure in an ultrafiltration experiment.

Claims (5)

[Claims] 1. A separation membrane comprising a polyisopropenyl acetate copolymer substantially consisting of a repeating unit represented by the general formula (I). Embedded image (Where A represents a vinyl monomer residue copolymerizable with isopropenyl acetate, m and n, x and y represent mol%, respectively, m = 100 to 1 and n = 1
00-m, x = 100-0 and y = 100-x) 2. The separation membrane according to claim 1, wherein m is 50 to 1 mol%. 3. The separation membrane according to claim 1, wherein m is 50 to 1 mol% and y is 100 mol%. 4. The separation membrane according to claim 1, wherein the copolymerizable vinyl monomer is methyl methacrylate. 5. The separation membrane according to claim 1, wherein the copolymerizable vinyl monomer is vinyl acetate or a saponified product thereof.