JPS5916988A - Cation exchange membrane for diaphragm salt electrolytic cell - Google Patents

Abstract

PURPOSE:To make the titled membrane mountable to any type of a diaphragm electrolytic cell without losing electrolytic capacity as well as to make the same inexpensive, by adhering a fluorine-contained polymer with a specific thickness to the periphery of a cation exchange membrane in a picture frame shape. CONSTITUTION:After a cation exchange membrane, especially, a fluorine contained cation exchange membrane is preliminarily swollen, the swollen membrane is fixed or fixed in a stretched state and, after drying treatment, a fluorine contained polymer film with a thickness of 0.05-0.5mm. is adhered to the periphery of the fixed membrane in a picture frame shape.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cation exchange membrane formed by bonding a fluorine-containing polymer film around a cation exchange membrane in a frame-like manner, and particularly to a cation exchange membrane having carboxylic acid groups and sulfonic acid groups as ion exchange groups. The present invention relates to a cation exchange membrane that can be used in place of asbestos in a salt electrolytic cell using a conventional asbestos diaphragm.

As a method for obtaining halogen and alkali by electrolyzing an aqueous alkali metal halide solution, a diaphragm method using asbestos as a diaphragm is becoming mainstream in place of the mercury method from the viewpoint of pollution prevention.

However, with this diaphragm method, highly pure caustic alkali cannot be obtained, and since only low concentration caustic alkali can be obtained, the obtained caustic alkali must go through complicated means such as concentration and separation, making it difficult to save energy. This is an extremely disadvantageous way to go against the current trend of discouragement.

On the other hand, the so-called ion-exchange membrane method, which uses an ion-exchange membrane as a diaphragm, is a method in which higher-purity, higher-concentration caustic alkali is directly obtained by electrolysis, and various technological developments for this method have been proposed. There is. Although this ion exchange membrane method is an extremely excellent method, it requires new equipment investment.For this reason, if an ion exchange membrane is installed in place of asbestos in the existing asbestos-based diaphragm electrolytic cell, the equipment cost will be reduced. It is an effective method that can obtain highly concentrated and highly purified alkali with only a small amount of use, and is also useful for saving energy, and its development is desired.

In response to these demands, the present inventors have investigated the amount of iron in order to create an ion exchange membrane that can be attached to any type of asbestos diaphragm battery, thereby making it extremely inexpensive and without sacrificing electrolytic performance. In general, it can be expected that the fluorine-containing cation exchange membrane mentioned above can be directly processed into various shapes, and the cation exchange membrane itself can also be made into a cylindrical bag by heat-sealing or other means. It is also possible and known to have a shape.

1- However, cation exchange membranes are expensive, the adhesive strength between membranes is low and it is not practical, and heat fusion is only possible on straight sections, making it difficult to create complex shapes. It is extremely difficult.

The present invention solves these problems all at once.

That is, the present invention is applicable to any type of diaphragm electrolytic cell in which a fluorine-containing polymer film of a certain thickness is bonded around a fluorine-containing cation exchange membrane having ion exchange groups. A feature of the present invention is that an expensive cation exchange membrane is used only in the current-carrying part, and an inexpensive fluorine-containing polymer film is used in the other parts, so that the joints can be easily removed. Although it increases, it is cheaper overall, there is no reduction in current efficiency due to peeling due to weak adhesive strength, there is no disadvantage such as being in the explosion range of gas, and furthermore, the adhesive part Compared to the conventional method, which requires very high-precision tools for straight sections but curved sections, the present invention uses almost no mechanical means and uses extremely simple means such as fusion bonding to achieve the object of the present invention. It is to be achieved.

As the ion exchange membrane used in the present invention, any membrane made of a polymer containing a cation exchange group such as a carbonic acid group, a sulfonic acid group, or a phosphonic acid group can be used. From the viewpoint of durability and heat resistance, it is preferable to use a fluorine-containing polymer.

Further, the ion exchange membrane does not necessarily need to have only one type of exchange group. Of course, it is also possible to use membranes with different ion exchange groups on one side and the other side, or membranes with a mixture of two or more types of exchange groups.

Considering both the electrolytic performance and the good bonding strength between the fluorine-containing polymer film and the cation exchange membrane,
A particularly preferred embodiment is an ion exchange membrane having a two-layer structure in which the cathode side has a weakly acidic exchange group such as a carboxylic acid group and the anode side has a strongly acidic exchange group such as a sulfonic acid group.

These ion-exchange membranes are manufactured by various conventionally known methods, but if necessary, fabrics made of fluorine-containing polymers such as polytetrafluoroethylene and/or general synthetic resins may be used. A cation exchange membrane reinforced with a woven fabric such as a net, a nonwoven fabric, a porous material, etc. is acceptable, and it is desirable to use a cation exchange membrane having a thickness of 20 to 500 μm, preferably 50 to 400 μm.

The ion exchange membrane used in the present invention is preferably a frame-shaped fluorine-containing polymer film that has been swollen in advance before adhesion, fixed or stretched, and then dried.

The reason for this is that cation-exchange membranes generally swell by 5 to 15% in water due to the cation-exchange groups they possess.In contrast, fluorine-containing heavy membranes hardly swell, so they do not swell in dry conditions. If a fluoropolymer film is bonded around a cation exchange membrane and immersed in an electrolyte,
Since only the cation exchange membrane is extended, many wrinkles occur in the cation exchange membrane.

For this reason, these wrinkles are caused by an increase in voltage due to the retention of air bubbles during electrolysis, and wrinkles at the joints cause distortion in the membrane, resulting in a decrease in the adhesive strength of the membrane, or in extreme cases,
To prevent negative effects such as peeling, it is preferable to carry out the above pretreatment before bonding. In the method of fixing or stretching the cation exchange membrane, it is necessary to pre-fix the membrane to a size that will swell under electrolytic operation conditions. It consists of stretching and fixing, and the method is not particularly limited. The first step is to swell the cation exchange membrane. Any method may be used to swell the membrane as long as it can swell the membrane to a desired size. It may be immersed in pure water, an aqueous solution of common salt or caustic soda, or an organic solvent (for example, an alcohol such as methanol). In addition, it is also possible to take measures such as heating at the same time to make it swell further, and it is also possible to take measures such as spraying or brushing without immersing it in the liquid. The drying method may be any conventional method.

That is, two window frame-shaped molds made of a strong material such as metal of a predetermined size are made, two gaskets are sandwiched between them, and the membrane swollen by the above method is placed in the gasket. Tighten and secure with scissors, shako vise, tie rod, etc. At this time, if the cation exchange membrane is tightened too much, it may cause creep and breakage, so be careful not to tighten it too much, and choose an appropriate tightening pressure so that it does not shift during drying. eDrying This may be done in a dryer, but it is sufficient to leave it fixed in a frame in the atmosphere for at least 1 hour. It is also more desirable to dry the membrane more completely using dry nitrogen.

When the cation exchange membrane treated in this way is used to bond the membrane and the fluorine-containing polymer film, the bonding method is not particularly limited, but it is generally done using an impulse heater or hot press. From the viewpoint of adhesive strength, a bonding method using heat fusion bonding is preferable. The bonding of the ion exchange membrane and the fluorine-containing polymer film, which is an important component of the present invention, will be described next.

Various fluorine-containing polymer films are commercially available, and among them, 4-fluoroethylene-6-propylene copolymer (hereinafter abbreviated as FEP film) and 4-fluoroethylene-propylene copolymer are particularly popular.
Two types of films made of fluorinated ethylene-perfluorovinyl ether copolymer (hereinafter abbreviated as PFA films) have a high bonding strength with cation exchange membranes, and the films themselves have very good processability. It is extremely effective for a reason.

In addition, the thickness of the above film is 0.05 to 0.5 f.
A range of i is preferred. The reason for this is that if the thickness is below the above range, it is possible to bond with a cation exchange membrane, but the film is thin and the strength of the film itself is low. Moreover, the thickness of the bonded area becomes thinner and the strength further decreases. One of the reasons for the thinness of the film is that it is extremely difficult to process the films together.
If the thickness exceeds the above range, the above-mentioned problems are mostly solved, but the biggest problem is the bonding strength between the fluorine-containing polymer film and the cation exchange membrane. Even when bonded, the adhesive strength is extremely small and cannot be used in practical use, so it is essential to use a bond within this range.

The method for joining the cation exchange membrane and the fluorine-containing polymer film is not particularly limited, and any method may be used as long as the adhesive strength can withstand electrolysis. According to the studies conducted by the present inventors, i) A particularly preferred example has good performance as a cation exchange membrane. For example, a cationic membrane having no reinforcing material and having ion exchange groups consisting of only sulfonic acid groups between polymer films, such as Nafiyonna 11 (trade name) sold by Devon Co., Ltd.
7. 115. This is a method of joining fluorine-containing polymer films in the shape of a picture frame using an inoles heater with an intervening film such as +125. Power 10~40Kg/c
1 hour 10-20 seconds, or if the frame film is PFA, temperature 330-400°C pressure 10-40 9/c+
+! If it is bonded for a time of lO~20 seconds, the adhesive strength is extremely strong and the electrolytic performance hardly deteriorates even after long-term electrolysis, and the electrolytic layer shows almost no wrinkles or creases. Also, the adhesive strength decreases.
No phenomena such as peeling of the joints were observed.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited thereto.

First, FIG. 1 shows an example of a cation exchange membrane with a frame-shaped fluorine-containing polymer film of the present invention. In this figure, (a) is a cation exchange membrane, (b) is a fluorine-containing polymer film, and (c) is a cation exchange membrane with a frame-shaped fluorine-containing polymer film. (a), (bl-(c)) show several examples of manufacturing methods. The fluorine-containing polymer film (B) molded into the cation exchange membrane (A) is bonded to the cation exchange membrane (A).
) →, (b) is a process of sequentially joining fluorine-containing polymer films (b) cut into strips (bar 1).
), a method for producing a cation exchange membrane with a frame-shaped fluorine-containing polymer film (bar 2) of the present invention, and (C) two fluorine-containing polymer films with different thicknesses ((B)- 1,
It is also possible to prepare (b)-2) and bond it to a cation exchange membrane. A feature of this method is that when it is impossible to bond a thick fluorine-containing polymer film directly to a cation exchange membrane, or when the adhesive strength is extremely weak even if it is bonded, a thin fluorine-containing polymer film can be prepared in advance. Strong adhesive strength can be obtained by bonding a polymer film and then a thick fluoropolymer film, and thick fluorine-containing≠fluoropolymer has very good processability.

FIG. 2 shows examples of various processing methods for the cation exchange membrane of the present invention. In general, diaphragm electrolytic cells have complex electrode shapes (e.g. finger type, cylindrical type) to increase the current carrying area compared to the floor area. For example, diaphragm electrolytic cells have a complex electrode shape (e.g. finger type, cylindrical type). There are various types of batteries, such as bipolar batteries, Hooker type, diamond type, and Shoden type, which are a combination of a box-type cathode can with holes and an anode arranged in a comb-like shape from the bottom. , is a cation exchange membrane that can be attached to any type of diaphragm electrolytic cell, and the explanation will be given using an example of a method of processing a cation exchange membrane for attaching to a granol cell, but of course it is not limited to this. do not have.

In FIG. 2(a), the cation exchange membrane of the present invention is folded in half (9). The upper and lower fluorine-containing polymer film portions of the folded membrane are joined halfway (2). Then, by unfolding the part that was not joined, a bag with a flared edge can be created. By connecting a large number of these, it is possible to create a multilayer membrane that can be attached to a granol tank type electrode.

FIG. 2(b) also shows that the cation exchange membrane of the present invention is first folded in half (9) 0 The ends of the upper and lower fluorine-containing polymer films of the folded membrane are all joined (2) ,
A cation exchange membrane bag is created (5). Holes are made in a fluorine-containing polymer sheet prepared separately (■ Insert bag-like membranes into these holes and join the circumferences of the holes to form a multi-layer membrane.M Figure 2 (e) ) also uses the cation exchange membrane of the present invention.

First, a part of the frame-shaped fluorine-containing polymer film is molded (I). Fold the film along the dotted line, place another fluorine-containing polymer film on the top and bottom, and join together to form a finger-shaped bag membrane (6). By joining these together, a multi-bag membrane is created. (2)

[Brief explanation of the drawing]

Figure 1 (a), (b), (c) (c) shows an example of a cation exchange membrane with a frame fluoropolymer film of the present invention. Figure 1 shows a cation exchange membrane of the present invention. In Figure 0, which shows an example of the membrane manufacturing method, (A) shows the cation exchange membrane used, (B) shows the fluorine-containing polymer film, and the thick line part (C) in the figure shows the cation exchange membrane used. indicates the joint. FIG. 2 shows several examples of methods for forming the cation exchange membrane with a frame fluorine-containing polymer film produced in FIG. 1 into a bag shape or a bag-like continuous membrane. In the figure, dotted lines indicate the folded portions, the bonded portions between the frame film and the cation exchange membrane are omitted, and only the bonded portions during molding into a bag-like or bag-like continuous membrane are shown in thick lines. Patent applicant: Toyo Soda Kogyo Co., Ltd. Figure 2 (1) (b) (m) (1
) (b) (IID(
v) Tsukuda)

Claims (1)

[Scope of Claims] 1. A cation exchange membrane for a diaphragm salt electrolytic cell, which is formed by joining a fluorine-containing polymer film having a thickness of 0.05 to 0.5 mm around the cation exchange membrane in a frame shape. 2. The fluorine-containing polymer film contains 4-fluorinated ethylene-6
Fluorinated propylene copolymer or tetrafluoroethylene
A cation exchange membrane according to claim 1, which is a film made of a perfluorovinyl ether copolymer. 3. After the cation exchange membrane bonded to the fluorine-containing polymer film is swollen in advance before bonding. The cation exchange membrane according to claim 1 or 2, which is a cation exchange membrane that has been fixed or stretched and fixed, and then dried. 4. Bonding temperature: 300-400°C, pressure: 10-40K
The cation exchange membrane according to claims 1 to 3, which is carried out under bonding conditions of f/c-d and time of 10 to 20 seconds.