JPH05123549A - Water permselective pervaporation membrane - Google Patents

Abstract

PURPOSE:To provide the subject membrane excellent in both of separation capacity and permeability using a pervaporation method. CONSTITUTION:A first dense layer composed of chitosan and a second dense layer formed by crosslinking a crosslinkable silicone resin are provided on a porous support membrane and the first dense layer is covered with the second dense layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water permselective pervaporation membrane, and more particularly to a water permselective pervaporation membrane for selectively separating water from an aqueous solution of an organic substance by a pervaporation method.

[0002]

2. Description of the Related Art The pervaporation method is a method in which a liquid mixture to be separated is supplied to the primary side (stock solution side) of a separation membrane and the secondary side (permeation side) of the membrane is depressurized or carrier gas is aerated. By doing so, a pressure difference is applied between the primary side and the secondary side of the membrane, and a specific substance to be separated is permeated through the membrane to the secondary side of the membrane in a gaseous state to be separated. Such pervaporation method is an azeotropic mixture which is difficult to separate by the distillation method,
In recent years, it has attracted attention as one of separation techniques that enable separation of a mixture of organic compounds and isomers having boiling points close to each other.

Various proposals have heretofore been made for such a pervaporation method. For example, US Pat. Nos. 2,953,502 and 3,035,060 propose water / ethanol separations using acetyl cellulose membranes and polyvinyl alcohol membranes. Also, Japanese Examined Japanese Patent Publication Sho 63-39
Japanese Patent No. 281 proposes a pervaporation method using a chitosan membrane. In addition to these, although various membranes to be used in the pervaporation method have been proposed, most of them have problems such as insufficient separation performance and permeation rate, or difficulty in membrane production, and thus are put into practical use. Most are not.

However, among the above, the chitosan membrane has been attracting attention in recent years as a membrane used in the pervaporation method.
For example, it is known that high separation performance can be obtained by using chitosan as a sulfate (Polymer Preprint
s, Japan, Vol. 38, No. 7, p. 1967 (1989)), it is generally difficult to stably obtain a membrane having both high separation performance and permeation performance with chitosan alone.

[0005]

The present invention has been made in order to solve the above-mentioned problems in the membrane separation by the conventional pervaporation method. It is an object of the present invention to provide a water permselective pervaporation membrane that is used.

[0006]

A water permselective pervaporation membrane according to the present invention comprises a porous support membrane, a first dense layer of chitosan and a second dense layer of a crosslinkable silicone resin crosslinked. And the first dense layer is covered with the second dense layer. The porous support membrane is not particularly limited as long as it does not swell with water vapor or the vapor of the organic compound contained in the aqueous solution to be separated, but usually polyimide, polysulfone, poly Ultrafiltration membranes and microfiltration membranes made of ether sulfone, polyamide, polyacrylonitrile, polyvinyl alcohol, polyolefin etc. are preferably used. In particular, an asymmetric membrane is preferably used.

The water permselective pervaporation membrane according to the present invention comprises:
On such a porous support membrane, there is a first dense layer made of chitosan and a second dense layer obtained by crosslinking a crosslinkable silicone resin. In the present invention, chitosan, which is the hydrophilic polymer forming the first dense layer, contains chitin, which is a constituent component of the shell of crustaceans such as shrimp and crab, in an alkaline solution in a concentration range of 30 to 50%, for example, It is a substance obtained by heating the mixture with an aqueous sodium hydroxide solution at a temperature of 60 ° C. or higher to deacetylate it. Such chitosan is D-
A polysaccharide having a chemical structure consisting of β- (1 → 4) bond having glucosamine as a basic unit, which is easily dissolved by forming a salt in a dilute aqueous solution of acetic acid, hydrochloric acid, phosphoric acid, etc. When contacting this with an alkaline aqueous solution, again
It has the property of solidifying and precipitating.

[0008] Generally, chitosan is a general term for deacetylated products obtained by treating chitin with concentrated alkali as described above. Chitosan used in the present invention has a degree of deacetylation so that it is excellent in film-forming property. Usually 50% or more, especially
It is preferably 70% or more. Furthermore, in the present invention,
Chitosan may be cross-linked with a cross-linking agent such as glycerol polyglycidyl ether, etc., if necessary, and the dense layer of chitosan may contain an additive.

In the present invention, the dense layer of chitosan can be obtained by applying the above-mentioned aqueous solution of chitosan on the porous support membrane, drying it, and heat-treating it if necessary. As a solvent for preparing an aqueous solution of chitosan, a dilute aqueous solution of acetic acid, hydrochloric acid, phosphoric acid or the like is usually used. In the present invention, the crosslinkable silicone resin for forming the second dense layer means a silicone resin which is soluble in an organic solvent before crosslinking but gives an insoluble resin in the organic solvent after crosslinking. Such crosslinkable silicone resins have various reactive groups at the ends of each molecular chain, and are crosslinked with each other by the reactive groups, optionally in the presence of a crosslinking agent or a curing agent.

Such a crosslinkable silicone resin is usually represented by the general formula

[0011]

[Chemical 1]

Or

[0013]

[Chemical 2]

Or

[0015]

[Chemical 3]

(Wherein p + q = n), in which X represents a reactive group, R ² represents an alkyl group or an aryl group, and some of the repeating units have the general formula

[0017]

[Chemical 4]

It may also be. R ² is the same as above.
In the above formula, n is usually 10000 to 300000.
It is a number that has an average molecular weight of. In the above general formula, examples of the reactive group X include a vinyl group, an acryloxyalkyl group, a methacryloxyalkyl group, a hydroxyl group, a hydroxyalkyl group, an acyloxy group, an alkoxy group, an aminoalkyl group, a carboxylalkyl group, a ketoxime group, Examples thereof include an alkylamino group and an amide group. Part of R ² may be such a reactive group. R ² is typically a methyl group or a phenyl group.

Various types of crosslinkable silicone resins having the above-mentioned reactive groups are already known and can be obtained as commercial products. When the crosslinkable silicone resin having a reactive group at the terminal of the molecular chain as described above is crosslinked, a crosslinking agent, a curing agent or a polymerization initiator is used, if necessary. In order to coat the film made of chitosan as the first dense layer with the second dense layer obtained by crosslinking the crosslinkable silicone resin, the above-mentioned crosslinkable silicone resin is usually used in an appropriate organic solvent. Dissolve into a solution, apply this solution on the film made of chitosan,
It may be crosslinked.

The organic solvent for forming the organic solution of the crosslinkable silicone resin is not particularly limited and may be appropriately selected depending on the resin, and examples thereof include an aliphatic hydrocarbon solvent, an aromatic hydrocarbon solvent and an alcohol solvent. , Carboxylic acid type solvents, ester type solvents, ketone type solvents, ether type solvents, halogenated hydrocarbon type solvents and the like. The water permselective pervaporation membrane according to the present invention thus has a second dense layer formed by forming a first dense layer of chitosan on the porous support membrane and then crosslinking the crosslinkable silicone resin. Can be obtained by forming. Here, these two dense layers have a total thickness of usually 0.05 to 50 μm, preferably 0.2 to 20 μm. Have. This is because if the thickness of these dense layers is too thin, defects are likely to occur in the film, while if they are too large, the dense layer has poor transmission performance.

The water permselective pervaporation membrane according to the present invention comprises:
It may be in any form such as a flat membrane, an annular membrane, a hollow fiber membrane, and a membrane module equipped with such a membrane is also a plate-and-frame type, a spiral type, a hollow fiber type, etc., depending on the purpose of use. You can choose. The water permselective pervaporation membrane according to the present invention, various organic compounds containing water, for example, alcohols, esters, ethers, nitriles, hydrocarbons, halogenated hydrocarbons or mixtures thereof, especially, It can be used in a pervaporation method for separating water from an aqueous solution.

[0022]

The water permselective pervaporation membrane according to the present invention has a first dense layer made of chitosan and a second dense layer obtained by crosslinking a crosslinkable silicone resin on a porous support membrane. The first dense layer is covered with the second dense layer, and there are no dense layer defects such as staining stains in a pervaporation film including a conventional chitosan film, and there are no dense layer defects. Since it has superior separation performance and permeation performance of selectively permeating water as vapor as compared with a chitosan membrane, water can be efficiently separated from an aqueous solution of an organic compound by a pervaporation method.

[0023]

The present invention will be described below with reference to reference examples and examples, but the present invention is not limited to these examples. In the following, the film performance of the pervaporation film was evaluated by the following method. That is, the obtained membrane was attached to a pervaporation membrane performance evaluation device with an effective membrane area of 39.6 cm ² ,
Water / ethanol aqueous solution (weight ratio 5/95) at 70 ℃ is supplied to the primary side of the membrane, and the secondary side is 3 mmHg by a vacuum pump.
The pressure was reduced below. In this way, the mixed vapor permeating through the membrane is condensed with liquid nitrogen and collected, and after weighing, its composition is analyzed by gas chromatography, and the permeation flux Q
(Kg / m ² · hr) and water separation factor for ethanol α
Was calculated. The separation coefficient α is defined by the following equation.

[0024]

[Equation 1]

Here, X _W and X _E are the concentrations (% by weight) of water and ethanol in the water / ethanol solution on the primary side, and Y _W and Y _E are the water and ethanol in the water / ethanol solution on the secondary side. Is the concentration (% by weight). Further, the stain and stain test of the pervaporation membrane was carried out by the following method. That is, the obtained pervaporation membrane was attached to the same pervaporation membrane performance evaluation device as described above, and an aqueous solution / ethanol / aqueous dye solution (weight ratio 4.9 / 95 / 0.1) was supplied to the primary side, After pervaporation was carried out for 30 minutes by the same method, the membrane was taken out from the apparatus and visually inspected for the presence of staining stains on the surface of the dense layer. Example 1 1 g of chitosan having a deacetylation degree of 86% was dissolved in 98.5 g of a 1% acetic acid aqueous solution, and 0.5 g of a crosslinking agent glycerol polyglycidyl ether was added thereto to prepare 100 g of a 1% concentration chitosan solution. This solution was applied on a polyacrylonitrile-based porous film, air-dried at room temperature, and then heat-treated at 120 ° C. for 20 minutes to form a chitosan film having a thickness of about 0.5 μm on the porous film to form a composite film. Obtained. The permeation flux Q of this composite membrane was 0.876 kg / m ² · hr and the separation coefficient α was 366.

When the composite membrane was subjected to a staining stain test by the method described above, more than ten staining stains were found on the film surface. Then, an isooctane solution (concentration: 5%) of a crosslinkable silicone resin containing a crosslinking agent is applied on the chitosan film of the above composite film and heated at 90 ° C. for 15 minutes to evaporate isooctane and to crosslink the silicone resin. Was formed. The thickness of the thus-obtained film composed of chitosan and crosslinked silicone was about 1 μm.

The permeation flux Q of the composite membrane thus obtained was 0.775 kg / m ² · hr and the separation coefficient α was 2775. That is, it is understood that by forming a crosslinked membrane made of a crosslinkable silicone resin on the chitosan membrane, the separation coefficient can be remarkably increased while maintaining the large permeation flux of the chitosan membrane. Further, this composite film was subjected to a staining stain test by the method described above, but no staining stain was found on the film surface. Comparative Example 1 2 g of chitosan having a deacetylation degree of 86% was dissolved in 97 g of a 1% acetic acid aqueous solution, and 1 g of a crosslinking agent was added thereto to prepare 100 g of a 2% concentration chitosan solution. This solution was repeatedly applied twice on a polyacrylonitrile-based porous film, air-dried at room temperature, and then heat-treated at 120 ° C. for 20 minutes to form a chitosan film having a thickness of about 2 μm on the porous film, and a composite film Got The permeation flux Q of this composite membrane is 0.182 kg / m ² · h
The r and the separation coefficient α were 523.

This composite membrane has a slightly higher separation coefficient than the previously prepared chitosan membrane, although the dense layer of chitosan is four times thicker.
On the other hand, it is understood that the permeation flux is significantly reduced. However, this composite film did not show staining stains.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Iwama 1-2-1, Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation (72) Inventor Kaoru Furukawa 6-2-1, Nakajima-cho, Minatojima, Chuo-ku, Kobe Parity 3-1406 (72) Inventor Shoichi Kuroda 1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc. (72) Soichiro Shibata 1-3-1, Uchisaiwai-cho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Ltd. (72) Inventor Noriyuki Shimamura 1-3 1-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc.

Claims (1)

[Claims] 1. A porous support membrane comprising a first dense layer made of chitosan and a second dense layer obtained by crosslinking a crosslinkable silicone resin, wherein the first dense layer is the second dense layer. A water permselective pervaporation membrane characterized by being covered with a dense layer.