JPH0316624A - Composite membrane and its production - Google Patents

Abstract

PURPOSE:To obtain the composite membrane excellent in permeability, separative performance and mechanical strength and capable of being used in the industry by forming the thin layer of a hydrophilic natural polymer on a partially hydrolyzed polyacrylonitrile-based based membrane. CONSTITUTION:The polyacrylonitrile-based base membrane is partially hydrolyzed by the solid-liquid contact method which is left standing in aq. alkali or a soln. of alkali in alcohol or the like. The thin layer of a hydrophilic natural polymer is then formed on the base membrane by dipping in an aq. polymer soln., coating with a bar coater, spin coater, etc. The polysaccharides such as a water-soluble cellulose derivative is used as the hydrophilic natural polymer. Since the base membrane is partially hydrolyzed, the affinity for the thin layer is improved, and the thin layer with less defects is formed. Consequently, a membrane excellent in durability, permeability and separative performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a composite membrane and a method for manufacturing the same. More specifically, the present invention relates to a composite membrane in which a thin film made of a hydrophilic natural polymer is formed on a partially hydrolyzed polyacrylonitrile base material, and a method for producing the composite membrane.

[Prior art] The use of composite membranes in various separation processes has been considered, and these methods include pervaporation membranes, vapor permeation membranes, reverse osmosis membranes, and ultrafiltration membranes, depending on the separation method. It is also called a dehumidifying membrane.

In particular, the pervaporation method, in which the liquid mixture to be separated is completely passed through the feed liquid side (primary side) of two chambers separated by a separation chamber, removes water from a water-organic liquid mixture. However, it is attracting attention as a highly energy-efficient separation technology, and various composite models are being studied.

In order to improve the permeation performance of these composite membranes, it is important to make the membrane as thin as possible, but if the membrane becomes too thin, the permeation performance will increase, but the mechanical strength will decrease. Practically speaking, a support is required to supplement the strength.

In recent years, studies have been made to obtain membranes with excellent permeability and mechanical strength by forming thin membranes on base membranes, and various membranes have already been proposed. For example, JP-A-59-109204 discloses a composite separation membrane in which an active layer made of polyvinyl alcohol or the like is formed on a microporous support layer, as described in JP-A-60-78601 and JP-A-60.
-97002 discloses a composite separation membrane in which an active layer made of an acetylene polymer is formed on a microporous support layer. Furthermore, JP-A No. 62-255441 discloses a composite membrane in which a layer of polymer ion salt is provided between two ultrafiltration membranes, but the composite membrane disclosed in the above specification is This is extremely important in terms of the practical application of separation methods that satisfy all of the membrane permeation performance represented by the separation coefficient and permeation rate, as well as mechanical strength. There is a need for a composite membrane that has both excellent performance and is durable for practical use.

Therefore, an object of the present invention is to provide an industrially satisfactory composite component Ml that has excellent permeation performance, separation performance, and mechanical strength, and a method for producing the same.

[! Means for Solving Problem II] The present inventors have made extensive studies and have developed a composite membrane in which a thin layer made of a hydrophilic natural polymer is formed on a partially hydrolyzed polyacrylonitrile base membrane. We have discovered that this is a composite membrane that satisfies the performance, and have arrived at the present invention. That is, the present invention provides a composite membrane in which a thin layer of a water-soluble natural polymer is formed on a partially hydrolyzed polyacrylonitrile base membrane, and a method for producing the same.

The polyacrylic nitrile base film used in the present invention is
It is a membrane made of a polymer whose main constituent unit is acrylonitrile, and in the case of a porous membrane with large pores such as this polymer, when a thin layer made of a hydrophilic natural polymer is formed on the ItM4 group, pin Since holes are likely to occur and it is difficult to obtain a sufficient permeation flow rate with a substantially non-porous dense membrane, it is preferably microporous.
Tokurupyrrolidone, vinyl acetate, vinylpyridine, vinylidene chloride, vinylsulfonic acid, styrenesulfonic acid,
Examples include a copolymer having at least one unit with allylsulfonic acid, (meth)acrylic acid, etc., a polyacrylonitrile homopolymer, or a blend of the copolymer with another polymer.

In the case of a copolymer having acrylonitrile as the main constitutional unit, it is preferable that the acrylonitrile unit is contained in an amount of 50 mol % or more from the viewpoint of increasing affinity caused by hydrolysis.

The polyacrylonitrile base membrane may be in any form such as a flat membrane, a tubular membrane, or a hollow fiber membrane. In order to partially hydrolyze a polyacrylonitrile base film with a pore size on the order of microns, the structure of the base material gorge must be left standing in an alkaline aqueous solution or alkaline alcoholic aqueous solution, or passed through these solutions at a moderate speed. This can be achieved using solid-liquid contact methods such as Examples of the alkali that can be used include alkali metal hydroxides, amines, and mixtures thereof, and sodium hydroxide or potassium hydroxide is preferred as it is practical.

The degree of hydrolysis of polyacrylonitrile polymers is
It can be controlled by processing conditions such as concentration of alkali, temperature of alkaline solution and contact time, and the processing conditions are:
It is appropriately selected depending on the composition of the polymer or copolymer to be hydrolyzed, the heat resistance of the membrane, etc. Generally O. 1~
Processing conditions of 50-80° C. and 5-60 minutes in a 2N alkaline solution are chosen.

Hydrolysis of the acrylonitrile polymer is confirmed by the appearance or increase of absorption derived from carboxyl groups using an infrared absorption spectrum.Partially hydrolyzed polyacrylonitrile base film shows that carboxyl groups are used. It is in the form of various metal salts, amine salts, etc. depending on the type of alkali, but it can also be converted to the acid form by acid treatment. A partially hydrolyzed polyacrylonitrile base membrane can be used as a separation membrane as it is, but it can be used as a separation membrane by forming a thin layer of a hydrophilic natural polymer on the base membrane to create a composite membrane. In the present invention, it should be hydrolyzed as appropriate depending on the application within a range that can maintain the membrane form, since it is difficult to achieve functional effects such as anchorage, permeation rate, and mechanical performance. As mentioned above, in the present invention, partially hydrolyzing the polyacrylonitrile base film means hydrolyzing it to such an extent that the film form is maintained. Therefore, in the present invention, the membrane surface portion may be hydrolyzed by bringing an alkaline aqueous solution into contact with the membrane surface under various conditions.

Since it is made into a polyion complex, it is convenient for obtaining a high-performance and durable composite membrane.

Examples of hydrophilic natural polymers used in the present invention include chitosan, chitosan salt, chitosan derivative (salt), alginic acid, alginate, alginic acid derivative (salt), pectic acid (salt), carboxymethoxychitin, pullulan, carrageenan. , chondroitin sulfate, hyalonic acid, carboxymethoxycellulose, cellulose sulfate, and other water-soluble cellulose derivatives.

In the present invention, it is important to form tii+ made of a hydrophilic natural polymer on the partially hydrolyzed polyacrylonitrile base film that is the support layer, and this is the most distinctive feature. ing.

That is, the partially hydrolyzed polyacrylonitrile base film has a strong affinity with the hydrophilic natural polymer forming the thin layer, so that a thin layer can be easily formed. Furthermore, when using a cationic hydrophilic natural polymer such as chitosan as the thin layer, if the rylonitrile base membrane is a hollow fiber membrane, the thin layer may be formed on either the inner or outer surface of the hollow fiber membrane. After formation, the composite membrane of the present invention can be obtained by drying.

In order to increase the permeation flow rate of the resulting stirred membrane, it is preferable that the thin layer formed on the base membrane be as thin as possible, but this thickness may vary depending on the smoothness of the base membrane surface and the base material. It is limited by the affinity between the membrane and the natural polymer substance that forms the thin layer. The thickness of the thin layer can generally be controlled by taking these constraints into account and adjusting the concentration of the dope and the conditions of the various thin layer formation methods. In addition, depending on the material and properties of the active layer (thin layer), the composite membrane created can be used as a composite membrane for ultrafiltration, reverse osmosis, dehumidification, pervaporation, vapor permeation, etc. For forming a thin layer of a hydrophilic natural polymer on the substrate, known methods such as immersion in an aqueous polymer solution (dope solution), coating with a bar coater or the like, and tin coating can be applied. Polyacrylonitrile-based hollow fiber membrane (inner diameter 0.8smq outer diameter 1.4IIm+, fraction 1,000@
1300G) was immersed in an aqueous N/5 Mail solution of go''c for 10 minutes, the nitrile groups of the membrane were partially hydrolyzed.

A composite membrane was prepared in the same manner. 95 in the same manner as in Example 1
When dehydration was performed from a wt% ethanol aqueous solution,
Separation coefficient is 4.8, permeation rate is 1.1 kg/s"・br
(Comparative Example 1).

Example 2 and Comparative Example 2 0.8% by weight of Algi as a hydrophilic natural polymer liquid Example 1 and Comparative Example 1 The partially hydrolyzed polyacrylonitrile base material obtained in the Reference Example was 0.8% by weight. 3% by weight chitosan aqueous solution (0.
(containing 6 wt% acetic acid) for 1 hour, then air-dried.
A thin layer of chitosan acetate was formed on the outer surface of the base membrane. The thickness of the thin layer is approximately 0.0 mm based on the results of scanning electron microscopy. I
It was I1m.

Using this composite membrane, dehydration from a 95% by weight ethanol aqueous solution was carried out by pervaporation under the conditions of 60"C and secondary side pressure Q.6ssHg, resulting in a separation coefficient of 88 and a permeation rate of 0.27kg/1.・hr was obtained (Example!).
The same procedure as Example 1 was carried out using the unhydrolyzed polyacrylonitrile resin obtained in Reference Example as the base film (Example 2).
.

A composite membrane was prepared in the same manner as in Example 1, except that a 0.6% by weight sodium alginate aqueous solution was used as the hydrophilic natural polymer solution and the same base membrane as in Comparative Example 1 was used. When dehydration was performed by pervaporation, the separation coefficient was! ．． 7. The penetration rate was 6.0 kg/1·hr (Comparative Example 2).

Example 3 The composite membrane obtained in Example 1 was immersed for 2 minutes in an aqueous ethanol solution of N;/100 sulfuric acid (water/ethanol = 50/50 weight ratio), and the counteranion of chitosan in *m was converted to acetate ion. After converting it into sulfate ion, the 95% ethanol aqueous solution was dehydrated by the pervaporation method in the same manner as in Example 1. As a result, the separation coefficient was 320 and the permeation rate was 0.24 kg/s''·h. Ta.

The effects of the present invention are clear from the results of the above Examples and Comparative Examples.

[Effects of the Invention] According to the present invention, a composite membrane in which a thin layer made of a hydrophilic natural polymer is formed on a partially hydrolyzed polyacrylonitrile base membrane can be easily produced. This type of collar film has good affinity with the base material and the thin layer, so it is easy to form a thin layer with few defects, and it has good durability and permeation performance, so it can be used by pervaporation method, vapor permeation method. Dehydration from various water-organic liquid mixtures, dehumidification from air, etc.
It is also suitably used to separate aqueous mixtures by methods such as dialysis, ultrafiltration, and reverse osmosis.

Claims (1)

[Claims] 1. A composite membrane produced by coating a partially hydrolyzed polyacrylonitrile base membrane with a hydrophilic natural polymer. 2. The composite membrane according to claim 1, wherein the hydrophilic natural polymer is a natural polysaccharide. 3. The composite membrane according to claim 1 or 2, which is used for pervaporation. 4. When manufacturing a composite membrane by coating a polyacrylonitrile base film with a hydrophilic natural polymer, the polyacrylonitrile base film is partially hydrolyzed in advance to increase its hydrophilicity. A method for manufacturing a composite membrane.