JP3114985B2 - Separation membrane for water-soluble organic substances - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a separation membrane for a water-soluble organic substance. More particularly, the present invention relates to a water-permeable separation membrane which is extremely suitable for pervaporation (hereinafter abbreviated as PV) separation and vapor permeation separation.

In the PV method and the vapor permeation method, a liquid or vapor of an organic mixture (usually a mixture of water and an organic substance) is introduced to one supply side (or also referred to as a primary side) of a membrane with an appropriate polymer membrane as a boundary. By reducing the pressure on the other side (permeation side or secondary side) of the membrane or by flowing an inert gas, a partial pressure difference of the target component is provided on both surfaces of the polymer membrane, and the target component is converted into the primary side by the partial pressure difference. This is a separation method in which the gas is allowed to pass through to the secondary side and be taken out in a vaporized state. In the case of the present invention, water permeates from the primary side to the secondary side through the polymer membrane. In this method, a method of supplying a mixed vapor to the primary side is a vapor permeation method, and a method of supplying a mixed liquid is a PV method.

[Prior Art] The PV method and the vapor permeation method have attracted attention as a method for separating and concentrating an organic mixture which is difficult to separate by a normal distillation method. Such an organic mixture is one that forms an azeotropic mixture, one in which the boiling points of the components are similar, and one that contains a compound that is easily denatured by heat.
Alcohol-water mixtures such as methanol-water system, ethanol-water system, isopropanol-water system, acetone-
There are a ketone-water mixture such as an aqueous system, and an organic acid-water mixture such as an acetic acid-water system. Such a water-organic mixture which cannot be separated by a normal distillation method can selectively permeate water or an organic substance by using a PV method or a vapor permeation method, thereby separating the organic substance.

Regarding water-permeable membranes used for the separation of water-soluble organic substances by the PV method or the vapor permeation method, polyvinyl alcohol-based membranes and polyacrylonitrile-based membranes have been disclosed in U.S. patents, and many membranes have been patented in Japan since then. Has been disclosed. Representative examples of these membranes include regenerated cellulose, polyvinyl alcohol, cellulose acetate, dextrin, chitosan, polyethyleneimine, and polymers such as sulfonic acid groups and carboxylic acid groups. Such as a membrane into which an exchange group has been introduced.

First, this type of membrane is required to have high permselectivity to water, and second, to have a high liquid permeation amount. The permselectivity to water is evaluated by a separation coefficient α ^H20 represented by the following equation, and the larger the value, the better the separation.

The permeation amount of the liquid is represented by the permeation amount (kg) per hour per 1 m ^{2 of the} membrane area, based on the permeation speed = f (kg / m ² · h). The larger the value of f, the better the performance of the film.

Since both the separation coefficient and the permeation rate are greatly affected by the concentration and temperature on the primary side and the pressure on the secondary side, it is necessary to evaluate the membrane performance while keeping these conditions constant.

As described above, various types of water selectively permeable membranes have been disclosed. However, these membranes generally have the disadvantage that their separation factors are too low or their permeation rates are too low to be practical.

[Problems to be solved by the invention]

The problem to be solved by the present invention is to use a separation membrane having a large separation coefficient and a sufficiently high permeation speed as a separation membrane used for selectively permeating water of a water-soluble organic substance by a PV method and a vapor permeation method. It is to develop.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a separation membrane that effectively combines a regenerated cellulose layer and a polyvinyl alcohol layer has significantly improved the water separation coefficient in a water-soluble organic substance system. The present invention was found to be able to be obtained and the transmission speed could be maintained sufficiently high, and the present invention was completed. That is, the present invention relates to a separation membrane for water-soluble organic substances having a water-selective permeability, wherein the separation layer comprises two layers of a regenerated cellulose layer and a polyvinyl alcohol layer.

[Operation and Configuration of the Invention]
It is very suitable for separating water from water mixtures, ketone-water mixtures, organic acid-water mixtures.

The separation layer of the present invention is basically composed of a regenerated cellulose layer and a polyvinyl alcohol layer.

The regenerated cellulose layer used here is prepared by dissolving cellulose in an aqueous solution of a metal complex such as copper ammonia, copper ethylenediamine, or the like, or cellulose in a variety of amine solvents. Although it can be obtained from a dissolved solution or the like, a method of obtaining from a viscose solution is generally preferable. It is necessary that the constituent material of the separation membrane is not dissolved or degraded by water or the target organic matter, but the regenerated cellulose membrane is chemically stable, insoluble in water, and a common organic solvent. Is insoluble in
Suitable for a separation layer because of its high water permeability.

The regenerated cellulose layer of the present invention may be formed into a membrane by extruding the above solution from a die and performing an appropriate treatment, or may be formed on a porous film such as polyacrylonitrile, polysulfone, or polyethylene as a support membrane. It may be formed by coating on a substrate. In addition, cellophane, which is a general-purpose regenerated cellulose film obtained from the viscose method, can be used as it is.

The thickness of the regenerated cellulose layer is 2 to 25 μm, preferably 3
1010 μm. If the thickness does not reach 2 μm, the uniformity of the film is impaired, defects such as pinholes are likely to occur, and the film performance becomes unstable. Moreover, since it is made from a low-viscosity, low-concentration liquid, the film becomes mechanically weak. If it is larger than 25 μm, the transmission speed becomes too small and is not practical. The degree of polymerization of cellulose is not particularly limited, but is usually about 100 to 500.

If it is less than 100, the mechanical strength of the film tends to be weak, and if it is more than 500, it becomes a high viscosity solution,
The uniformity of the formed film thickness may be deteriorated, and the performance may be easily fluctuated.

The polyvinyl alcohol layer of the present invention is obtained by applying a polyvinyl alcohol solution, generally an aqueous solution, onto the regenerated cellulose membrane. The polyvinyl alcohol layer is also chemically stable like the regenerated cellulose layer,
It is insoluble in ordinary organic solvents. However, since the polyvinyl alcohol layer gradually dissolves in water, it is necessary to perform some kind of crosslinking treatment to make it insoluble in water.

This cross-linking treatment is performed by adding a cross-linking agent to an aqueous solution of polyvinyl alcohol, applying the aqueous solution to which the cross-linking agent is added onto a regenerated cellulose membrane, and performing heat drying and heat treatment at a relatively high temperature. As the cross-linking agent used for this purpose, those conventionally used are used, for example, dicarboxylic acid, dihalide,
Examples include, but are not limited to, aldehydes or dialdehydes. A typical example is maleic acid. If a polyvinyl alcohol aqueous solution containing several weight% of maleic acid with respect to polyvinyl alcohol is applied on the regenerated cellulose membrane and dried and heat-treated at 150 ° C., the membrane becomes insoluble in water. Becomes Further, in the present invention, a modified polyvinyl alcohol which is a copolymer with a monomer having a crosslinking effect can be used without using a crosslinking agent, and this aqueous solution is applied to a regenerated cellulose membrane, and dried and heat-treated. A water-insoluble polyvinyl alcohol film is also obtained. Copolymers such as maleic anhydride can also be used as this type of modified polyvinyl alcohol.

If the viscosity of the coating solution is too low when applying the aqueous polyvinyl alcohol solution onto the regenerated cellulose membrane, the regenerated cellulose membrane swells with water, does not become a film having a uniform thickness, and may adversely affect its separation performance. Therefore, the viscosity of the coating solution should be such that the coating solution does not completely penetrate into the regenerated cellulose film, stays near the surface to form a film, and finish the drying quickly after coating. preferable.

In addition, a means for preliminarily swelling the regenerated cellulose membrane with water, applying an aqueous polyvinyl alcohol solution thereon, and then drying and heat-treating is also effective for achieving uniform separation performance.

The thickness of the polyvinyl alcohol layer is 0.5 to 15 μm,
Preferably it is 1 to 6 μm. If it is less than 0.5 μm, uniformity is lost for the same reason as in the case of the regenerated cellulose layer, and mechanical strength is also reduced. If it is larger than 15 μm, the transmission speed becomes too small, which is not practical. The degree of polymerization of the polyvinyl alcohol used is not particularly limited as long as it has appropriate film-forming ability and film strength. The saponification degree is preferably as high as possible from the viewpoint of increasing the water resistance even slightly, but is not particularly limited.

Next, the overall configuration of the separation membrane of the present invention will be described with reference to the drawings. The separation membrane in FIG. 1 is a layer (1) formed by applying an aqueous solution of polyvinyl alcohol or modified polyvinyl alcohol on a regenerated cellulose layer (2) such as cellophane, followed by drying and heat treatment.

FIG. 2 shows a separation membrane in which the membrane of FIG. 1 is laminated on a porous support membrane (3) having excellent mechanical strength, such as polyacrylonitrile, and a regenerated cellulose layer (2) coated with polyvinyl alcohol is used. It may be laminated on the porous support film (3), or the regenerated cellulose layer (2) may be laminated on the porous support film (3), and then a polyvinyl alcohol layer may be applied on the regenerated cellulose layer (2) by a coating method. (1)
May be formed.

FIG. 3 shows a form in which a cellulose solution is applied on a porous support membrane (3), and then an appropriate treatment is performed to form a regenerated cellulose membrane, on which a polyvinyl alcohol layer (1) is applied by a coating method. Is a separation membrane. The present invention may have any of the configurations shown in FIGS. The shape may be any shape such as a flat membrane, a hollow fiber, and a spiral.

〔Example〕

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

<Explanation of Separation Experiment> Using the experimental apparatus shown in FIG. 4, membrane separation experiments of a vapor permeation method and a PV method were performed in an ethanol-water system and an isopropanol-water system. In the PV method, the primary side was filled with the mixture, and in the vapor permeation method, the mixture was filled with the equilibrium vapor of the mixture, and the mixture was stirred with a fan or a pump, respectively. The experimental conditions were as follows: the concentration of alcohol supplied to the primary side was 90% by weight, the temperature was 50 ° C, and the secondary side pressure was 2 Torr.
r. Attach the membrane with 2 polyvinyl alcohol layers
The next side. The effective area of the membrane is about 90 cm ² . Under these conditions, a water selective permeation type alcohol-water separation experiment was performed, and the results were evaluated by a separation coefficient and a permeation rate. However, the separation coefficient = ▲ α ^H20 _alcohol ▼ and the permeation rate = f (kg / m ² · h).

However, in FIG. 4, (10) is a separation membrane, (11) is a fan, (1)
2) is a motor, (13) is a cooler, (14) is a pump,
(15) shows a cooler, (16) shows a trap, and (17) shows a pump.

Example 1 Using dissolved pulp as a raw material, a cellulose concentration of 9.0%, a caustic soda concentration of 6.1% (both by weight) and a viscosity of 5% at 20 ° C.
A 000 cp viscose solution was prepared. The slit made by combining the viscose liquid with two stainless plates having a length of 40 cm so as to have a gap of about 80 μm, the sulfuric acid concentration was 150 g.
/, Extruded into a coagulation bath with a sodium sulfate concentration of 200 g / and a temperature of 45 ° C, and then passed sequentially through the same regenerating bath, temperature washing bath, and washing bath as in the cellophane manufacturing process, followed by chemical treatment and washing. It was dried in a multi-cylinder dryer to obtain a regenerated cellulose membrane having a thickness of about 6 μm.

Next, polyvinyl alcohol having a polymerization degree of 2000 and a saponification degree of 99 to 100% is dissolved in hot water at 85 ° C. to prepare a polyvinyl alcohol solution having a concentration of 70 g /. After cooling, the polyvinyl alcohol solution contains 5% by weight per polyvinyl alcohol. Was dissolved to obtain a polyvinyl alcohol solution containing a crosslinking agent.

The cross-linking agent-containing polyvinyl alcohol solution was applied onto the regenerated cellulose membrane using a Meyer bar, and then 15
Dried and heat-treated in a hot air dryer at 0 ° C for 1 hour, and regenerated cellulose film thickness 6 µm, cross-linked polyvinyl alcohol film thickness about 3
A separation membrane consisting of a regenerated cellulose layer and a polyvinyl alcohol layer having a total thickness of about 9 μm was obtained.
The separation experiment was performed using this membrane. The results are described below.

Experiment by vapor permeation method (a) Ethanol-water separation coefficient: ▲ α ^H20 _ETOH ▼ = 3,500 Permeation speed: f = 0.08 (kg / m ² · h) (b) Isopropanol-water separation coefficient: ▲ α ^H20 _IPA ▼ = 6,000 Permeation speed: f = 0.05 (kg / m ² · h) Experiment by PV method Isopropanol-water system Separation coefficient: ▲ α ^H20 _IPA ▼ = 2,000 Permeation speed: f = 0.15 (kg / m ² · h) Comparative example 1 In the same manner as in Example 1, a regenerated cellulose membrane having a thickness of about 9 μm was formed. Separation experiments were performed using this membrane to obtain the following data.

Experiment by vapor permeation method (a) Ethanol-water system Separation coefficient: ▲ α ^H20 _ETOH ▼ = 200 Permeation speed: f = 0.13 (kg / m ² · h) (b) Isopropanol-water system Separation coefficient: ▲ α ^H20 _IPA ▼ = 300 Permeation speed: f = 0.10 (kg / m ² · h) Experiment by PV method Isopropanol-water system Separation coefficient: ▲ α ^H20 _IPA ▼ = 100 Permeation speed: f = 0.24 (kg / m ² · h) Comparative example 2 100 g The polyvinyl alcohol solution containing a crosslinking agent was cast on a glass plate and immediately dried and heat-treated at 150 ° C. for 1 hour in a hot air drier. Thereafter, the film was cooled and peeled off from the glass plate to obtain a polyvinyl alcohol film having a thickness of about 9 μm. Separation experiments were performed using this membrane to obtain the following data.

Experiment using vapor permeation method (a) Ethanol-water separation coefficient: ▲ α ^H20 _ETOH ▼ = 350 Permeation rate: f = 0.08 (kg / m ² · h) (b) Isopropanol-water separation coefficient: ▲ α ^H20 _IPA ▼ = 500 Permeation speed: f = 0.07 (kg / m ² · h) Experiment by PV method Isopropanol-water system Separation coefficient: ▲ α ^H20 _IPA ▼ = 200 Permeation speed: f = 0.20 (kg / m ² · h) [Effect] The separation membrane composed of a combination of a regenerated cellulose layer and a polyvinyl alcohol layer in combination with a regenerated cellulose single membrane or a polyvinyl alcohol single membrane has an extremely high water permselectivity due to the synergistic effect thereof, as compared with the regenerated cellulose single membrane and the polyvinyl alcohol single membrane. It can be seen that the speed is maintained sufficiently high. Therefore, it is clear that the separation membrane of the present invention exerts high performance in separating water-soluble organic substances typified by an alcohol-water system.

[Brief description of the drawings]

1 to 3 are explanatory diagrams each showing an example of the separation membrane of the present invention. FIG. 4 is a schematic explanatory view of an apparatus used for measuring the characteristics of the separation membrane. (1) Polyvinyl alcohol layer (2) Regenerated cellulose layer (3) Porous support membrane

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Naoichi Sakota 1-23-24, Sumiyoshi Honcho, Higashinada-ku, Kobe, Hyogo (72) Inventor, Hideo Suematsu 5-28 Nishikujo, Konohana-ku, Osaka, Osaka Hitachi Inside Shipbuilding Co., Ltd. (72) Kazuo Harada, Inventor 5-3-28 Nishikujo, Konohana-ku, Osaka-shi Osaka Shipbuilding Co., Ltd. (72) Shiro Inoue 5-28, Nishikujo, Konohana-ku, Osaka-shi, Osaka No. Hitachi Zosen Corporation (72) Inventor Chuzo Isozaki 5-28 Nishikujo, Konohana-ku, Osaka-shi, Osaka Hitachi Zosen Corporation (56) References JP-A-63-7806 (JP, A) JP-A-64-80401 (JP, A) JP-A-64-38103 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 71/10 B01D 71/38

Claims (4)

(57) [Claims] 1. A separation membrane for a water-soluble organic substance, wherein the separation layer comprises two layers, a regenerated cellulose layer and a polyvinyl alcohol layer. 2. The separation membrane according to claim 1, wherein the separation layer is a layer formed by applying a polyvinyl alcohol solution on a regenerated cellulose membrane and regenerating the same. 3. The separation membrane according to claim 1, wherein the polyvinyl alcohol layer of the separation layer is a water-insoluble crosslinked polyvinyl alcohol layer. 4. The separation membrane according to claim 1, wherein said separation layer is supported by a porous support membrane.