JPS6268824A - Novel cation exchange membrane, production thereof and electrodialysis using said membrane - Google Patents

Abstract

PURPOSE:To obtain the titled exchange membrane, by previously roughening the surface of a cation exchange membrane and forming a thin high polymer layer having anionic exchange groups thereon, having improved stability without deterioration in selectivity and useful for electrodialysis of seawater, etc. CONSTITUTION:At least one surface of a cation exchange membrane which is preferably a hydrocarbon based resin having a three-dimensional skeleton of styrene and divinylbenzene as a basic structure and further sulfonic acid groups as exchange groups is roughened and a thin layer of a selective treating agent, i.e. a high polymer having anionic exchange groups, e.g. quaternized poly-4-divinylpyridine, is formed thereon to give the aimed exchange membrane. The surface roughening is carried out by irradiating, e.g. a polypropylene (PP) woven fabric with electron rays, feeding a monomer solution thereto, polymerizing the solution, placing a release sheet having affinity for the release sheet on the polymerized surface at the same time, completing the polymerization and peeling the release sheet to form a roughened surface having preferably 30 unevennesses having 0.05-1mu depth per mm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a cation exchange membrane with excellent permselectivity for monovalent cations and an electrodialysis method using the same. Specifically, a cation exchange membrane and its use for electrodialyzing an electrolyte solution containing two or more cations with different charges and selectively electrodialyzing cations with a small ionic charge. Conventional technology Conventionally, when concentrating seawater using an ion exchange membrane method for the production of common salt, a cation exchange membrane was used to remove sodium ions (
Selectively passing Calsula ion (Ca'') and Magnesium ion (Mg++) through Na+) has two advantages: prevention of gypsum scale precipitation in the concentrate and improvement of current efficiency for target cations. Various methods have been proposed to provide such selectivity, but basically, a thin polymer layer containing anion exchange groups is placed on the surface layer of a cation exchange membrane. This is achieved by forming.

As such a method, a method of simply contacting with an aqueous solution of a polymer having an anion exchange group (Japanese Patent Publication No. 46-2560
7, Japanese Patent Publication No. 53-44155), and a method of forming a three-dimensional layer within the surface layer after forming the surface layer (Japanese Patent Publication No. 47-1983).
3081), and a method of bonding the surface layer and the membrane matrix (Japanese Patent Publication No. 48-34676).

On the other hand, as an electrodialysis method, Japanese Patent Application Laid-Open No. 59-303 proposes a method in which one side of an ion exchange membrane is polished for the purpose of voltage reduction, and this side is brought into contact with a concentrated solution and electrodialyzed. . According to the example, it is shown that monovalent cation selectivity deteriorates when one side of the selectivity treatment is abraded by polishing and the polished surface is directed toward the dilution side.

In addition, for the soda electrolysis industry, Japanese Patent Application Laid-Open No. 56-1168
No. 91, JP-A No. 56-145927, etc., are known to have roughened fluorine-dyed cation exchange membranes, which prevent gases generated from the electrodes from adhering to the membrane surface during electrolysis. The purpose of this device is to reduce the voltage drop due to the voltage drop, and is characterized by being directly sandwiched between electrodes. Therefore, such roughened membranes have not been used in the field of electrodialysis, in which a large number of ion exchange membranes are stacked between electrodes, because there is no gas generation within the dialysis chamber.

Conventional treatment methods, such as three-dimensional membrane formation within the surface layer and membrane bonding with the matrix, have good sustained selectivity and stability, but they tend to raise the voltage of the membrane during treatment and are difficult to operate. Complicated and undesirable.

In addition, although the method of simply bringing the anionic polymer liquid into contact with the membrane is preferable because it is simple to operate, the stability of selectivity is poor, and as has been the case in recent years, the concentration of concentrated liquid is high and the membrane with high selectivity is not suitable for gypsum. It could not be said that it was sufficient to achieve the desired result from the viewpoint of preventing precipitation.

Furthermore, in recent years, the amount of organic matter and impurities in coastal seawater has increased, and red tides have often occurred.

If seawater contains such substances, should it be sterilized with chlorine and filtered? ! Even if it is supplied to a mad analysis tank and electrodialysis is performed, a phenomenon occurs that significantly deteriorates the permselectivity between monovalent cations and divalent cations, and due to this trouble,
Driving is interrupted.

For this reason, the stability of permselectivity has been required more than ever before.

Means for Solving the Problems The present invention does not solve the problems of selectivity, stability of permselectivity, and prevention of voltage increase due to processing by using a processing agent or a processing method as in the past, but by using a cation exchange method. These problems can be solved by improving the membrane matrix.

That is, the present invention is a cation exchange membrane in which at least one side of the cation exchange membrane is rough, and a thin layer having an anion exchange group is formed on this surface.

In this way, in order to roughen the surface condition of the cation exchange membrane matrix and form a thin layer of a selective treatment agent having anion exchange groups thereon, the selective treatment agent and thin layer forming method are conventionally known. Any selective treatment agent and method can be employed.

Preferably, the selective treatment agent is a quaternized product of poly-4-vinylpyridine, a quaternized product of polydialkylaminoalkylstyrene, a quaternized product of polysialgylaminoalkyls(meth)acrylamide, or a formalin condensation product of dicyandiamide. Condensation products of dicyandiamide and diethylenetriamine, etc. can be treated by dissolving these selective treatment agents in salt water and immersing them at a temperature above room temperature, or by diluting this solution in a dialysis tank and diluting it into a dilution chamber. There are methods such as passing liquid through and adsorbing it, or simultaneously applying electricity and electrodepositing.

As a result, compared to conventional membranes that are not roughened and subjected to selectivity treatment, the selectivity is less degraded and the stability is improved even when it comes into contact with red seawater or seawater containing anionic organic matter. , the selectivity was also good, and the voltage increase associated with the treatment was reduced.

The cation exchange membrane used in the present invention is preferably a homogeneous membrane whose main component is hydrocarbon.

Furthermore, those based on a three-dimensional skeleton of styrene or divinylbenzene and having a sulfonic acid group as an exchange group are more preferable. Of course, in order to increase the strength of the membrane, it may be lined with fibers, porous membranes, etc.

In the present invention, the rough surface of the cation exchange membrane may have at least 20 irregularities with a depth of 0.05 μm to 5 μm per square inch. Further, it is preferable that there are 60 or more unevennesses with a depth of 0.05 μm to 1 μm per 11111. Outside this range, the stability of permselectivity decreases.

To measure the roughness of the cation exchange membrane before selective permeation treatment, use a universal surface profile measuring device (Tybuna-7com 60B Tokyo Seimitsu KK) as disclosed in JP-A-56-116891, or the exchange membrane surface. and can be determined from cross-sectional electron micrographs. Furthermore, after performing selective permeation treatment, that is, if a thin layer of polymer having an anion exchange group is present on the surface, the thin layer on the surface is removed by a method such as soaking it in an aqueous salt solution. Then, after increasing the roughness with the surface thin layer by determining the surface roughness as described above or adsorbing heavy metals etc. to the cation exchange groups of the cation exchange membrane, the cross section of the membrane was measured using an electron microscope. It can be measured by methods such as

The method for obtaining a roughened film is as follows: - During polymerization, a substance that has affinity with the release sheet is added, phase separation occurs on the surface, and this film is sulfonated, which is chemically performed. Method for obtaining a rough surface film■ Method for obtaining a rough surface film by smearing with a rough release sheet, polymerizing the film, and removing the rough surface of the release sheet ■Glow discharge, dry plast, liquid honing, etc. Examples include a method of physically roughening the membrane surface of an ion exchange P or an exchange membrane intermediate to obtain a roughened membrane, but the present invention is not limited to these methods.

As a method of forming a thin polymer layer having anion exchange groups on this membrane and imparting selectivity between cations, any of the already known means described above can be employed. can.

Among these, the method of contacting with an aqueous polymer solution having an anion exchange group is particularly preferred as it is simple to operate and highly effective. In addition, it is preferable to include an organic substance that swells the membrane in the aqueous polymer solution to further improve selectivity.

EXAMPLES Explanation of the symbols used in the examples and measurement methods are as follows.

(a) Shows the specific permselectivity of magnesium ions to Na ions of the F Mg j cation exchange resin membrane.

However, N: Specified concentration of the relevant ion in the concentrated solution C: Measuring method of the specified concentration of the relevant ion in the diluted solution: Asahi Kasei electrodialysis equipment lid Acilizer 8■-4 type (effective current carrying area 2 dn/) according to the present invention Cation exchange membrane and anion exchange membrane (Asahi Kasei Aciplex (B'A-
Incorporate 10 pairs of 172) and dilute in the dilution chamber? af water (C
1--0,4N) at LV = 4 ern/set. After dialysis for 4 hours at 25°C and 3.5 A/d-, the circulation of the concentrate was stopped, and the concentrate overflowing from the concentration chamber was collected and analyzed as a concentrate, while it was discharged from the dilution chamber. Sample diluted seawater, analyze it as a diluted liquid, and calculate υFMg based on this composition.

The fact that the specific permselectivity of monovalent ions is large means that when FMg is small, so if F'Mg is made small, the specific permselectivity of monovalent ions is increased. Become.

Although the specific permselectivity of multivalent ions other than magnesium ions differs in absolute value, it is roughly proportional to the specific permselectivity of magnesium ions, so in the examples of this application, FMg is used to represent the specific permselectivity of multivalent ions. did.

(b) When measuring the specific permselectivity, 10 pairs of voltages are measured at the same time, and the cell voltage (V/p) for one pair is obtained from this.

Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 20 parts of divinylbenzene (purity 50%), 80 parts of styrene
1 part, 30 parts of benzyl ether, 0.2 parts of azobisisobutylnitrile, 1 part of 1,2-polybutadiene, and 0.21 parts of chlorobrene to prepare a monomer liquid.

Polypropylene woven fabric is irradiated with electron beams, filled with monomer liquid, and polyester films are stacked alternately.

The temperature is gradually raised from 40°C to 95°C, and polymerization takes place for 196 hours.

A portion of the polymer containing the polypropylene woven fabric (hereinafter referred to as thick film) and the polyester film are peeled off.

When the surface of the obtained thick film was observed with an electron microscope,
A large number of irregular pores with a pore diameter of 0.1 μm to 10 μm were formed on both surfaces, and the number was 10 or more (2000 or more per 1.5 pm).

This thick film was immersed in a solution of anhydrous sulfuric acid adduct in dichloroethane, sulfonated at 0°C for 120 hours, and then equilibrated with salt water to obtain a cation exchange membrane.

The surface of this cation exchange membrane is electron W! 4 When observed with a microscope, the pores observed in the thick film were still formed. Note that the depth of the holes was 0.1 μm to 1 μm.

In the end, I selected both sides using the two-pronged method described below.

We performed selective treatment, electrodialysis, and measured the characteristics.

Selectivity treatment-1 11000p of quaternized poly-4-vinylpyridine
Immerse in p salt aqueous solution at 95°C for 20 hours.

Selectivity treatment-2 Noniso Ndo AM (manufactured by Dai-Seiga Kogyo KK), 500 pp
m Salt aqueous solution (immerse at 35°C for 3 hours.

The results of the measured characteristics are shown in Table 1 along with comparative examples and other examples.

Comparative Example □ Monomer of Example 1, 1. ．． A thick, flexible ion exchange membrane was obtained in the same manner as in Example 1 using monomers other than 2-polybutadiene and chloroprene.

No pore formation was observed on the surface of this film even when observed with an electron microscope at a magnification of 20,000 times.

Example 2 Using the monomer of Comparative Example, the polyester film was replaced with a matted polyester film, stacked and polymerized, and the rough surface of the matted polyester film was transferred to obtain a thick film and a cation exchange membrane. This film had unevenness with a depth of 0.1 μm to 5 μm on both sides.

In addition, during the selection process, one side was covered with a polyester film so that only the uncovered side could be subjected to the selection process. During electrodialysis, the membranes were assembled so that one side subjected to the selection treatment faced the dilution side, and electrodialysis was performed.

Example 6 The thick film produced in the comparative example was roughened on only one side by a liquid honing method. An aqueous solution in which alumina (WA + 1500 manufactured by Fujimi Abrasives Industry KK) with an average particle size of 10 μm was suspended was mixed with 3.2Y! 6 per 1dm thick film with compressed air
The surface was roughened by spraying for a minute. On the roughened surface of this membrane, pores with a pore diameter of 2 to 10 μm were formed.

In addition, during the selection treatment, one side that was not subjected to the roughening treatment was covered with a polyester film, and only the one side that was subjected to the roughening treatment was subjected to the selection treatment. For electrodialysis, one side that had been roughened and subjected to selection treatment was assembled so that it faced the dilution side, and electrodialysis was performed.

Table 1: Roughness of membranes and measurement results of membrane properties after selective treatment Next, in order to investigate the effect of surface roughening, these membranes were treated with 100p of carrageenan (borian anion extracted from seaweed).
It was immersed in a pn1 salt aqueous solution at 25° C. for 3 hours to examine changes in properties. The results are shown in Table-2.

Table 2 Membrane property measurement results after immersion in carrageenan Furthermore, seawater containing Akashio was sampled at a salt factory, chlorine sterilized, and two-stage filtered, followed by electrodialysis using the membranes of Example 1 and Comparative Example. The water was supplied to the tank for 6 hours and then changed to normal seawater to stabilize the properties. The results are shown in Table-6.

Table 3 Results of dialysis with Akashio seawater Effects of the invention The present invention provides a cation exchange membrane in which at least one side of a cation exchange membrane is rough and a thin polymer layer having an anion exchange group is present on the other surface. By performing electrodialysis using a membrane with this surface facing the dilution side of electrodialysis, cations with low ionic charges can be removed from the dilute solution, which is an electrolyte solution containing two or more types of cations with different charges. Selectively electrodialyze. At this time, even if the diluted solution contains an anionic organic substance or an Akashio component, the selectivity is less likely to deteriorate and electrodialysis can be carried out stably. For this reason, in the case of electrodialysis for producing salt by concentrating seawater, it is necessary to take measures such as suspending operation and restoring selectivity even if seasonal red tide occurs or organic impurities increase. It is possible to continue stable operation without any problems.

Claims (4)

[Claims] (1) A cation exchange membrane in which at least one side of the cation exchange membrane is rough, and a thin polymer layer having an anion exchange group is present on at least one of the rough surfaces. (2) The rough surface of the cation exchange membrane is 0.05 μm to 5 μm.
The cation exchange membrane according to claim 1, wherein there are 20 or more unevenness per mm with a depth of m. (3) In a method for producing a cation exchange membrane in which a thin polymer layer having anion exchange groups is formed on the surface of a cation exchange membrane, the thin polymer layer is formed after roughening the surface of the cation exchange membrane. A method for producing a cation exchange membrane, characterized by forming a cation exchange membrane. (4) When electrodialyzing salt using an electrodialysis tank consisting of an anion exchange membrane and a cation exchange membrane, at least the dilution side of the cation exchange membrane has an anion exchange group on its rough surface. An electrodialysis method that electrodialyzes salt by arranging it so that it forms a surface with a thin layer of molecules.