JPH0149742B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating a cation exchange membrane.
Specifically, this is a method for treating a cation exchange membrane in which an H-type cation exchange membrane is treated with an aqueous solution containing hypochlorite ions. It is known that cation exchange membranes are widely used for separation of ions in solutions, concentration desalting or diffusion dialysis, organic chemical reactions, and the like. In addition, various methods for producing cation exchange membranes are known, but generally, cation exchange groups are often introduced after the production of a membrane-like product. In this case, that is, when a cation exchange group is introduced after the production of a membrane-like material, the introduction of the cation exchange group is generally carried out under severe conditions. That is, when a sulfonic group is introduced as a cation exchange group, treatment is performed with concentrated sulfuric acid, chlorosulfonic acid, fuming sulfuric acid, or a mixed acid thereof. The cation exchange membrane obtained in this manner is generally colored and has a brown to yellowish brown color, and is inferior in terms of commercial value.
In addition, due to long-term storage or mistakes in storage methods, some of the coloring may come off and the color may become mottled, further reducing the commercial value. In order to compensate for these conventional deficiencies, the present inventors
We have been trying to develop a method for producing cation exchange membranes that do not stain even under harsh conditions. However, if one attempts to manufacture a cation exchange membrane industrially, it has been found from experience that it is difficult to obtain a non-colored cation exchange membrane, although there may be differences in shading. Therefore, an attempt was made to decolorize the resulting cation exchange membrane. As a result, it was found that although various oxidizing agents can be used to decolorize, the so-called hydrocarbon-based cation exchange membranes in particular deteriorate, resulting in a decrease in the value of the product. Therefore, we have been conducting extensive research into techniques that can prevent the deterioration of cation exchange membranes and decolorize colored substances. As a result, the inventors found that the objective could be achieved by treating the H-type cation exchange membrane with an aqueous solution containing hypochlorite ions, leading to the completion of the present invention. The present invention is a method for treating a cation exchange membrane, in which an H-type cation exchange membrane obtained by introducing sulfonic acid groups after membrane formation is treated with an aqueous solution containing hypochlorite ions. The cation exchange membrane used in the present invention is not particularly limited. In the present invention, any cation exchange membrane obtained by previously forming a base material into a membrane shape and then introducing sulfonic acid groups may be used, and the sulfonic acid groups may be formed into sulfonic acid groups due to the process of introducing the sulfonic acid groups or other circumstances. When it is in the form of a salt, it is used by converting it into the H form (acid form) by a conventional method. Furthermore, cation exchange membranes are generally commercially available as Na-type and other salt-type cation exchange membranes due to factors such as storage stability and stability. However, when carrying out the treatment of the present invention, it is essential to use an H-type cation exchange membrane. Therefore, when using a commercially available cation exchange membrane, it is necessary to convert it into an H-type cation exchange membrane in advance. Although the reason for this is not clear, the inventors of the present invention assume the following. That is, when the H-type cation exchange membrane is brought into contact with an aqueous solution containing hypochlorite ions, hydrogen ions are dissociated in the aqueous solution.
It is therefore presumed that decolorization of the cation exchange membrane occurs due to accelerated decomposition of hypochlorite ions near the ion exchange groups. In the present invention, it is necessary to use an aqueous solution containing hypochlorite ions as the aqueous solution for treating the H-type cation exchange membrane. Generally, oxidizing agents or reducing agents are used to decolorize colored materials, and chlorine, hydrogen peroxide, etc. are known. Although it is possible to decolorize the cation exchange membrane, which is the object of the present invention, by treating it with these oxidizing agents, the cation exchange membrane may be eluded, the ion exchange membrane may be destroyed, or the so-called cation exchange membrane may deteriorate. In extreme cases, the cation exchange membrane becomes porous and loses its original properties as an ion exchange membrane. Therefore, it is generally not practicable to treat cation exchange membranes with oxidizing agents. However, in the present invention, by using an aqueous solution containing hypochlorite ions, it is possible to decolorize the cation exchange membrane without deteriorating it. The concentration of hypochlorite ion may be determined in relation to the industrially adopted treatment time; if the concentration is high, the treatment time may be short; conversely, if the concentration is low, the treatment time may be long. It takes. Generally, when carrying out the present invention industrially, a range of several minutes to about 24 hours is preferred, and in this sense, a range in which the hypochlorite ion concentration is 10 to 100,000 ppm, preferably 50 to 10,000 ppm is most widely used. Of course, it is also possible to carry out the treatment outside the above range by appropriately selecting the treatment temperature, treatment time, etc. Furthermore, when the concentration of hypochlorite ions increases, the hypochlorite ions decompose to generate chlorine ions, which causes deterioration of the cation exchange membrane. This tendency is particularly noticeable when the aqueous solution is acidic, and even if the hypochlorite ion is within the above range, handling becomes troublesome. Therefore, it is generally preferable to use the aqueous solution containing hypochlorite ions of the present invention in a neutral or alkaline state. However, if the alkalinity becomes strongly alkaline, the hypochlorite ion becomes stable, which not only requires a long treatment time, but also tends not to produce a noticeable decolorizing effect. Therefore, the PH of an aqueous solution containing hypochlorite ions
Generally, it is most suitable to carry out at about 6.5 to 13.8. The means for adding hypochlorite ions to the aqueous solution is not particularly limited, and any known method can be employed. In general, alkali metals or alkaline earth metals of hypochlorous acid, such as sodium hypochlorite, potassium hypochlorite, and calcium hypochlorite, are preferred because they are inexpensive and easily available. These hypochlorite salts generally exhibit alkalinity when dissolved in an aqueous solution due to their industrial manufacturing method, and therefore are optimal as a means for imparting hypochlorite ions of the present invention. The treatment means for treating the H-type cation exchange membrane in the present invention with an aqueous solution containing hypochlorite ions is not particularly limited. Generally, the H-type cation exchange membrane may be immersed in the aqueous solution, or the cation exchange membrane may be set on a moving aid such as a belt conveyor, roller conveyor, etc. provided in the aqueous solution and brought into continuous contact with the membrane. As is clear from the above description, the present invention not only decolorizes the cation exchange membrane to become a colorless cation exchange membrane and doubles its commercial value, but also changes the performance of the cation exchange membrane by the treatment of the present invention. Not at all. In addition, since the cation exchange membrane obtained by the process of the present invention is generally in the form of an H-type cation exchange membrane, it is preferable to change it to a Na-type cation exchange membrane and store it as necessary. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be given below, but the present invention is not limited to these Examples. In the following examples, the deterioration of the cation exchange membrane is expressed as a change in ion exchange capacity as a criterion. Example 1 Na-type cation exchange membrane (manufactured by Tokuyama Soda Co., Ltd.,
(trade name, Neocepta CL-25T) was cut to 50 mm x 50 mm and treated with an IN-HCl aqueous solution to obtain an H-type cation exchange membrane. This H-type cation exchange membrane had an ion exchange capacity of 1.8 mlg/g dry membrane and was brown in color. Next, it was immersed for 16 hours in an aqueous solution (PH12.5) containing sodium hypochlorite (manufactured by Tokuyama Soda Co., Ltd.) as a treatment agent at a concentration of 500 ppm. The obtained cation exchange membrane has an ion exchange capacity of 1.8mlg/
There was no change in ion exchange capacity at 100 g. Moreover, the obtained cation exchange membrane was decolored to colorless. Comparative Example 1 In Example 1, H-type cation exchange membrane was not used.
The same procedure as in Example 1 was conducted except that a Na-type cation exchange membrane was used. As a result, the color of the Na-type cation exchange membrane remained almost the same as before treatment, and it was not possible to decolorize it. Comparative Example 2 The same procedure as in Example 1 was carried out except that hydrogen peroxide and sodium percarbonate were used instead of sodium hypochlorite in Example 1. As a result, the cation exchange membrane treated with an aqueous hydrogen peroxide solution was bleached colorless, but the ion exchange capacity was 1.5mlg/
g decreased to a dry film. Furthermore, the color of the ion exchange membrane treated with an aqueous sodium percarbonate solution was almost the same as that of the ion exchange membrane before treatment, and the color could not be decolored. Example 2 The same procedure as Example 1 was carried out except that the various conditions in Example 1 were changed as shown in Table 1. The results are shown in Table 1.

[Table] Example 3 The same procedure as in Example 1 was carried out except that potassium hypochlorite and calcium hypochlorite were used instead of sodium hypochlorite in Example 1. As a result, the ion exchange capacity of the ion exchange membrane is
There was no change in ion exchange capacity at 1.8 mlg/g dry membrane. Moreover, the obtained cation exchange membrane was decolored to be colorless.

Claims (1)

[Scope of Claims] 1. A method for treating a cation exchange membrane, which comprises treating an H-type cation exchange membrane obtained by introducing sulfonic acid groups after membrane formation with an aqueous solution containing hypochlorite ions. 2. The method according to claim 1, wherein the aqueous solution containing hypochlorite ions is a neutral or alkaline aqueous solution. 3 The hypochlorite ion in the aqueous solution is 10~
The method according to claim 1, wherein the amount is 100000 ppm. 4. The method according to claim 1, wherein the aqueous solution containing hypochlorite ions is an aqueous solution containing an alkali metal or alkaline earth metal salt of hypochlorous acid.