JPH0278426A - Laminated membrane and production thereof - Google Patents

Abstract

PURPOSE:To enhance the hydrophilic property of a laminated membrane as a general separating membrane by partially hydrolyzing a polyacrylonitrile base membrane and coating the base membrane with a hydrophilic synthetic polymer. CONSTITUTION:A membrane of polyacrylonitrile, a blend or copolymer of polyacrylonitrile with other material or cross-linked polyacrylonitrile is partially hydrolyzed by dipping in a soln. of an acid or alkali such as KOH, NaOH or Ba(OH)2 or by bringing only the surface of the membrane into contact with the soln. The excess soln. is then removed by washing and the membrane is dried. The resulting hydrophilic base membrane is coated with a hydrophilic synthetic polymer such as polyacrylic acid or PVA to enhance the hydrophilic property. A hydrophilic separating membrane is easily obtd. and used for various purposes such as permeation of steam, dialysis, reverse osmosis and dehumidification of air.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable not only to water selective permeation membranes using pervaporation or vapor permeation methods, but also to reverse osmosis and ultraviolet membranes. It relates to a wide range of general separation membranes, such as filtration and air dehumidification membranes. Further, the membrane structure such as a dense layer or a porous layer is not limited, and the membrane form may be any of flat membranes, hollow fiber membranes, tube membranes, etc., and can be arbitrarily determined depending on the application.

[Prior Art and Problems] General hydrophobic separation membranes have been subjected to various hydrophilic treatments in order to improve their shortcomings, such as the surface being difficult to wet with water and easily drying out, and prone to adsorption and clogging.

As a conventional hydrophilic treatment for separation membranes, it is common practice to add polyhydric alcohols such as polyethylene glycol and glycerin to the membrane. However, when hydrophilicity is imparted to the separation membrane by such a method, there is a drawback that these additives are eluted into the f-liquid during use. Also, special public service 1986-1618
No. 7 discloses a method in which a water-soluble polymer is coated on a hydrophobic separation membrane by immersion, and then subjected to water insolubilization treatment to make it hydrophilic by electron beam irradiation, heating crystallization, and chemical reaction with formaldehyde or glyoxal. However, in the case of such a method, the operation is complicated, so it is impractical and defects are likely to occur. Furthermore, Japanese Patent Laid-Open No. 58-35862 discloses a method of sputter etching a polysulfone filtration membrane in a vacuum discharge atmosphere as a method for making a hydrophobic microporous filtration membrane hydrophilic. However, this method has the disadvantage that the mechanical strength of the microporous 3-filtration membrane after the hydrophilic treatment is significantly reduced.

[Means for Solving the Problems] As a result of extensive research in order to solve the above problems, the present inventors succeeded in obtaining a polyacrylonitrile-based separation membrane that was subjected to a hydrophilic treatment using a simple method. Of course, this membrane can be used as it is as a hydrophilic separation membrane, but it can also be used as a base membrane when coating a hydrophilic polymer. That is, the present invention consists of the following configuration.

(1) A composite membrane produced by coating a partially hydrolyzed polyacrylonitrile base membrane with a hydrophilic synthetic polymer.

(2) When manufacturing a composite membrane by coating a polyacrylonitrile base film with a hydrophilic synthetic polymer, the polyacrylonitrile base film is partially hydrolyzed in advance to increase its hydrophilicity. A method for manufacturing a composite membrane.

The permeation rate in pervaporation performance evaluation in the present invention is
Kg/m in permeation mixture amount per unit membrane area/unit time
Expressed in units of '・hr. On the other hand, the separation coefficient (α) is the ratio of water and organic matter in the permeate gas to the ratio of water and organic matter in the feed liquid or feed vapor. That is, α − (
X/Y)/(X/Y).

It is p. Here, X and Y represent the respective compositions of water and organic matter in a two-component system, and p and r represent permeation and supply, respectively.

The membrane material may be a blend or copolymer of polyacrylonitrile and other materials, and it is clear that crosslinking is preferable from the viewpoint of maintaining the membrane shape. Typical methods for hydrolyzing these materials include immersion in acid or alkaline solutions. Among these, the method of immersing in an alkaline solution such as potassium hydroxide, sodium hydroxide, barium hydroxide, etc. is particularly preferable from the viewpoint of the balance between the hydrolysis rate and maintaining the membrane shape. The degree of hydrolysis varies depending on the type of membrane material and whether it is a blend, copolymer, or crosslinked product, but depending on the type and concentration of the acid or alkali used, and the treatment time, an appropriate degree of hydrolysis can be achieved. It can be turned into dust. Although it differs depending on the material, it is not preferable to completely hydrolyze the membrane material because it is often converted into a water-soluble gel-like substance. Also 1. The object of the present invention can be achieved even if only the surface of the membrane is brought into contact with the treatment liquid and hydrolyzed.

Further, the reaction route of hydrolysis of polyacrylonitrile with an alkaline solution is thought to proceed approximately as shown in equations (+) to (V).

(See margin below) ↓OH- In a properly hydrolyzed membrane, the carboxyl group becomes an acid type, various metal salt type, amine salt type, etc. depending on the treatment liquid, and can be used as a separation membrane as it is. Furthermore, this hydrophilized separation membrane can be used as a base membrane and its surface can be coated with a hydrophilic polymer to easily enhance functionality. Typical examples of hydrophilic synthetic polymers include synthetic polymers such as polyacrylic acid and polyvinyl alcohol, but are not limited thereto. °
When the coating liquid is an anionic polymer such as polyacrylic acid, it is preferable to form a polyion complex with a cationic polymer in terms of improved membrane performance and stability. Specific examples of cationic polymers include, but are not limited to, polyethyleneimine, polyallylamine, polyvinylvinylone, and anionic polymers containing a quaternary ammonium salt in the main chain. . Moreover, polyion complexation can be easily achieved by simply immersing the coated membrane in these solutions. In addition, when anionic groups such as carboxyl groups are formed on the surface of the base film,
It is clear that even if the cationic polymer is coated first, it will be easily applied due to interactions between ions.

[Example] Next, the present invention will be explained in more detail with reference to Examples.

Example 1 D tJY- which is a polyacrylonitrile-based ultrafiltration membrane
M flat membrane (manufactured by Daicel Chemical Industries, Ltd., polyacrylonitrile content approximately 70%) was mixed with INN aO [78% in an aqueous solution.
Hydrolysis was carried out by immersion at -85°C for 30 minutes. After hydrolysis, excess alkali in the membrane is washed with water, dried, and then AT
As a result of measuring Ft-[R, 1400, I 550cm
The presence of ionized carboxyl groups was recognized from the absorption at the -' position, and it was confirmed that the membrane had been subjected to aqueous treatment. In addition, the water/ethanol separation performance (evaluation liquid: 95% ethanol, 60°C) was measured using this hydrophilic membrane using the pervaporation method, and the water selectivity was evaluated. The speed was 1 kg/m"·hr.

Comparative Example I The water selectivity of the DUY-M flat membrane was evaluated in the same manner as in Example 1 without being subjected to hydrolysis treatment. As a result, the separation coefficient was approximately 1, indicating that it had no water selectivity.

Comparative Example 2 A DUY-M flat membrane was placed in a 1N-NaOH aqueous solution at 78-8
Hydrolysis was carried out by immersion at 5° C. for 60 minutes.

This film had been converted to an excessive amount of sodium polyacrylate, and had become a gel-like substance with a broken film morphology.

Example 2 Hollow fibers (inner diameter/outer diameter = 1.0/1.5 mm) made of polyacrylonitrile polymer (content rate approximately 90%)
) using 5 mini-modules with a membrane area of approximately 70 cm.
created. Using this mini module, lN inside the thread.
-NaOH was passed at 80° C. for 15 minutes to lightly hydrolyze the inner surface. After passing a 0.5% aqueous solution of polyacrylic acid with a molecular weight of about 4 million for 10 seconds inside this hollow fiber,
After drying with hot air at a temperature of .degree. C., a 2% aqueous solution of CA-107, an ionene polycation having the following structure, was passed therethrough to form a polyion complex, and the mixture was further dried with ventilation. After repeating the above polyacrylic acid coating to polyion conjugation process twice to reduce defective areas, the water selectivity was evaluated in the same manner as in Example 1. As a result, all 5 monoyls showed high separation coefficients exceeding 800. In the case of this evaluation method, if there are few defects such as uneven coating, the separation coefficient becomes large, so it can be said that the film is coated fairly uniformly.

Comparative Example 3 The membrane was coated with a polyion complex in the same manner as in Example 2, except that the polyacrylonitrile hollow fibers were used as the base membrane for the composite membrane without being hydrolyzed. When the performance was evaluated, 3 out of 5 modules had a separation coefficient of over 800.

Example 3 - Hydrolysis treatment was carried out in the same manner as in Example 2 except that the polyacrylonitrile hollow fibers were not coated.
% PCA-107 aqueous solution was passed through the hollow fiber to form a polyion complex. Example of this membrane! The membrane performance was evaluated in the same manner as above, and after a separation factor of 3, the permeation rate was 10 kg/n+"-hr"-.

Example 4 The same treatment as in Example 3 was carried out except that hydrolysis was not performed. The membrane performance of this membrane was evaluated in the same manner as in Example 1. As a result, the separation coefficient was approximately 1, and there was no water selective permeability.

[Effects of the Invention] According to the present invention, conventionally commercially available reverse osmosis membranes, ultrafiltration membranes, precision 9 filtration membranes, etc. can be used as they are, without using advanced technology unlike conventional methods. However, a hydrophilized separation membrane can be easily obtained by contacting with an acid or alkaline aqueous solution for a predetermined period of time and hydrolyzing the membrane. Furthermore, when the hydrophilized separation membrane according to the present invention is used as a base membrane for a composite membrane, it has good affinity with the membrane surface when coated with a hydrophilic polymer, making coating easier. The hydrophilized separation membrane according to the present invention exhibits excellent water selective permeability by pervaporation, and can be used not only for dehydration from various organic mixed solutions, but also for vapor permeation, dialysis, and reverse water permeation by taking advantage of its properties. A wide range of applications can be used, such as infiltration and air dehumidification.

Patent applicant: Director-General of Basic Industries Bureau, Ministry of International Trade and Industry

Claims (2)

[Claims] (1) A composite membrane produced by coating a partially hydrolyzed polyacrylonitrile base membrane with a hydrophilic synthetic polymer. (2) When manufacturing a composite membrane by coating a polyacrylonitrile base film with a hydrophilic synthetic polymer, the polyacrylonitrile base film is partially hydrolyzed in advance to increase its hydrophilicity. A method for manufacturing a composite membrane.