JPS6252624B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for cleaning an ion exchange membrane. Ion exchange membranes are used in various fields. For example, electrolysis of alkali metal salts of mineral acids; seawater, brine,
It is used for desalting or concentrating electrolyte-containing solutions such as industrial water, stock solutions for food and pharmaceutical manufacturing, and industrial wastewater. Generally, electrolysis using an ion exchange membrane, electrodialysis,
When electrodialysis is performed, dissolved organic substances are often contained in the stock solution, and these dissolved substances are deposited on the surface of the membrane or even on the surface layer of the membrane during long-term operation. This causes membrane clogging and increases in electrical resistance, resulting in a significant drop in efficiency.Furthermore, as the thickness of the deposited layer increases, the critical current density decreases during electrodialysis and electrodialysis, and water in this deposited layer decreases. Decomposition may occur, resulting in the precipitation of alkaline scale, making electrodialysis impossible.
Therefore, when such a phenomenon occurs, it is necessary to clean the ion exchange membrane. Conventionally, physical cleaning methods and chemical cleaning methods are known for cleaning ion exchange membranes, but these known methods are still not fully satisfactory in terms of cleaning effects and prevention of membrane deterioration. It wasn't. For example, as a physical cleaning method, a small ball of sponge is passed through the battery container and the friction between the small ball and the membrane surface is used to clean the battery, or the battery case is disassembled, the ion exchange membrane is taken out, and each individual membrane is cleaned using a sponge, etc. There is a method of removing deposits by scrubbing with a cleaning tool or the like. However, although these cleaning methods can remove deposits on the surface of the membrane, removal of organic matter deposited on the surface layer of the membrane is incomplete and often results in damage to the membrane. Additionally, chemical cleaning methods have the advantage that membranes can be easily cleaned by immersing the membrane in an appropriate chemical solution or by circulating the chemical solution within a device incorporating the membrane. There is. However, the chemicals conventionally used for chemical cleaning of membranes tend to cause membrane deterioration, such as a decrease in mechanical strength and ion selective permselectivity, and the cleaning effect obtained is unsatisfactory. It has its drawbacks. For example, when an acid or alkali aqueous solution is used as a cleaning solution, the effect of removing deposits is small, and during long-term use, the membrane is likely to deteriorate due to hydrolysis of the polymeric substance that constitutes it. In addition, when using an aqueous solution of oxidizing substances such as hypochlorous acid or hydrogen peroxide as the cleaning liquid,
While the organic matter deposited on the membrane is oxidized and decomposed, the ion exchange membrane is also exposed to an oxidizing atmosphere.
There are drawbacks that may include deterioration. The present inventors have been conducting research on the production of ion exchange membranes and the use of ion exchange membranes for many years. In particular, research has been carried out on the cleaning and regeneration of ion exchange membranes whose performance has deteriorated due to the deposition of organic substances.
As a result, by contacting the ion exchange membrane with a mixed solution of water and an organic solvent containing a sodium salt or potassium salt of mineral acid or carboxylic acid and sodium hydroxide, potassium hydroxide, or ammonium hydroxide, the ion exchange membrane They have discovered that the performance of ion exchange membranes can be restored without deteriorating the membrane, and have completed and proposed the present invention. That is, the present invention provides an ion exchange membrane in which the ion exchange membrane is brought into contact with a mixed solution of water and an organic solvent containing a sodium salt or a potassium salt of a mineral acid or a carboxylic acid, and containing sodium hydroxide, potassium hydroxide, or ammonium hydroxide. This is a cleaning method. In addition, the present invention provides a method in which electricity is supplied to a battery container in which an ion exchange membrane is set.
Also provided is a method for cleaning an ion exchange membrane by passing a mixed solution of water and an organic solvent containing a sodium or potassium salt of a mineral or carboxylic acid and sodium hydroxide, potassium hydroxide or ammonium hydroxide. In the present invention, a mixed solution of water and an organic solvent is used to clean an ion exchange membrane, and the mixed solution contains a sodium salt or a potassium salt of a mineral acid or a carboxylic acid, and sodium hydroxide, potassium hydroxide, or ammonium hydroxide. It is necessary to include. The sodium salt or potassium salt of the mineral acid or carboxylic acid is not particularly limited, and known salts used for cleaning ion exchange membranes can be used. Sodium or potassium salts of mineral acids, such as, for example, sodium chloride, potassium chloride, sodium sulfate, sodium carbonate, sodium nitrate, potassium nitrate, are generally preferably used. It is also possible to use sodium or potassium salts of carboxylic acids such as sodium acetate, potassium acetate, sodium citrate, potassium citrate, and sodium oxalate. As described below, the sodium salt or potassium salt of these mineral acids or carboxylic acids is used together with an alkali compound selected from sodium hydroxide, potassium hydroxide, or ammonium hydroxide, so they react in a mixed solution of water and an organic solvent. Preferably, those that do not cause precipitation. Therefore, it is preferable to use a sodium salt or potassium salt of the mineral acid or carboxylic acid that does not generate precipitates depending on the type of alkali compound. In general, the concentration of the sodium salt or potassium salt of mineral acid or carboxylic acid used is within the range where it can be dissolved in a mixed solution of water and an organic solvent, and it is preferable to use it at a high concentration. In general, it is preferable to use a 0.1 to 3.0N aqueous solution or a mixed solution of 0.1 to 3.0N at a level below the saturated solubility. The alkaline compound used in the present invention is preferably one of sodium hydroxide, potassium hydroxide, and ammonium hydroxide. The concentration of the alkaline compound used is not particularly limited, and can be used in a wide range from low concentration to saturated solubility depending on the degree of contamination of the ion exchange membrane. However, some types of ion-exchange membranes are degraded by high concentrations of the alkali compound, so it is preferable to determine the concentration of the alkali compound in advance depending on the type of ion-exchange membrane. Generally, a 0.01 to 3.0N aqueous solution, preferably a 0.5 to 2N aqueous solution, is most widely used. The organic solvent used in the present invention is not particularly limited and may be used as long as it has permeability to the ion exchange membrane, but in general, when handled as a mixed solution with water, the mixed solution becomes a homogeneous system. Preferably. In particular, lower alcohols such as methanol, ethanol, propanol and butanol, glycols such as ethylene glycol and propylene glycol, and lower ketones such as acetone and methyl ethyl ketone are preferably used from the above viewpoint. In the present invention, the mixing ratio of water and organic solvent is determined by the type of mineral acid or carboxylic acid, sodium salt or potassium salt, sodium hydroxide, potassium hydroxide or ammonium hydroxide, organic solvent, etc., or by cleaning the ion exchange membrane. It varies depending on the cleaning means used, temperature, time, etc., and cannot be absolutely limited. Generally, the most widely used range is a mixing ratio of the organic solvent in the mixed solution of 5 to 80% (by weight), preferably 30 to 70% (by weight). The most important feature of the present invention is that, as described above, a mixed solution of water and an organic solvent is used as a cleaning liquid, and the mixed solution contains mineral acid or carboxylic acid, sodium salt or potassium salt, sodium hydroxide, hydroxide, etc. Contains potassium or ammonium hydroxide. Even if the mixed solution lacks any of the sodium salt or potassium salt of mineral acid or carboxylic acid, and sodium hydroxide, potassium hydroxide, or ammonium hydroxide, a sufficient cleaning effect cannot be exhibited. Similarly, even if any of the sodium salt or potassium salt of the mineral acid or carboxylic acid and sodium hydroxide, potassium hydroxide, or ammonium hydroxide is present, the present invention applies even if a single solvent of water or an organic solvent is present. The effects of the invention are not fully demonstrated. Although it is currently not clear what mechanism of action achieves the effects of the present invention, the inventors of the present invention speculate as follows. That is, the sodium salt or potassium salt of mineral acid or carboxylic acid and sodium hydroxide, potassium hydroxide or ammonium hydroxide have the effect of desorbing pollutants chemically bonded to the ion exchange membrane from the ion exchange membrane. It is believed that sodium hydroxide, potassium hydroxide, or ammonium hydroxide maintains the desorbed contaminants in a dissociated state and facilitates their migration out of the ion exchange membrane. It is also believed that the organic solvent acts to facilitate the movement of contaminants to the outside of the ion exchange membrane. Therefore, each of these roles will act synergistically to remove contaminants from the ion exchange membrane almost completely in a short period of time. In general, a decrease in performance of an ion exchange membrane due to deposition or binding of contaminants to the ion exchange membrane can be determined by measuring the AC resistance value of the ion exchange membrane. That is, when contaminants are deposited or bonded to the ion exchange membrane, the electrical resistance value is higher than that of a fresh ion exchange membrane. As is clear from the examples, the method of the present invention has the excellent effect of reducing the electrical resistance of the ion exchange membrane, which has become high due to deposition or bonding of contaminants to the ion exchange membrane, to its original resistance value. Demonstrate. As is clear from the above description, the ion exchange membrane that is the object of the present invention has a tendency to cause contaminants such as organic substances to deposit or bind to the ion exchange membrane due to use or long-term storage, which deteriorates the performance of the ion exchange membrane. It has been lowered. However, the type of ion exchange membrane is not particularly limited, and any known ion exchange membrane may be used. For example, a cation exchange membrane having a functional group such as a sulfone group, a carboxyl group, or a phosphonic group as an ion exchange group; a quaternary ammonium group;
These include anion exchange membranes having functional groups such as amino groups and imino groups; and amphoteric ion exchange membranes having these functional groups at the same time. Furthermore, the resin composition of the ion exchange resin is not particularly limited, and includes hydrocarbon-based ion-exchange resins such as styrene-divinylbenzene copolymer; halogen-containing ion-exchange resins containing fluorine, chlorine, etc.; perfluoro-based ion-exchange resins; It may be any ion exchange resin or the like. In the present invention, the means for cleaning the ion exchange membrane is not particularly limited, and any known means can be employed. For example, the battery case may be dismantled, the ion exchange membranes may be taken out, and the ion exchange membranes may be brought into contact with the cleaning solution, either individually or in groups, or the operation of the battery tank may be stopped and the cleaning solution may be passed through. Just choose. Although it is preferable to use a circulating method for the cleaning liquid, a stationary method can also be used. Generally, the most suitable method is to place the ion exchange membrane in a cleaning tank and circulate the cleaning liquid through the cleaning tank, or to circulate the cleaning liquid in a battery tank. In particular, an embodiment in which the ion exchange membrane is washed while it is set in a battery container is advantageously adopted industrially. When cleaning in this case, it is preferable not only to circulate the cleaning liquid but also to carry out the cleaning while the battery container is energized. It is preferable to conduct the current in a direction opposite to the direction in which the current is normally applied (generally referred to as reverse energization) rather than to conduct the current as is normally applied to the container. Cleaning the ion exchange membrane by reverse current flow not only restores the ion exchange membrane, which has been contaminated and has increased electrical resistance, to the performance of the ion exchange membrane before use, but also improves the performance of the ion exchange membrane during reuse. It has the advantage of being highly effective in preventing contamination over a long period of time. The contact temperature, contact time, etc. between the ion exchange membrane and the cleaning liquid in the present invention are not particularly limited, and may be appropriately determined in advance depending on the degree of contamination of the ion exchange membrane, the type of cleaning liquid, etc. Generally 0℃~50
The most widely used conditions are washing temperatures of preferably 20-40°C for 30 minutes to 24 hours, preferably 1 to 5 hours. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples. Example 1 A strongly acidic cation exchange membrane having a resin skeleton made of styrene-divinylbenzene copolymer [manufactured by Tokuyama Soda Co., Ltd.].
NeoSepta. CL-25T] and strongly basic anion exchange membrane [manufactured by Tokuyama Soda. NeoSepta. ACH−45T〕
We installed 500 pairs of these in a dialysis tank with an effective energized area of 0.25 m ² to desalinate seawater and produce drinking water. the result,
Organic matter contained in seawater adhered to the ion exchange membrane surface and the electrical resistance of the ion exchange membrane increased, so the voltage to be applied to the electrodialysis tank was reduced from 0.7V per pair at the beginning of operation to 1.2V. rose to Therefore, a cleaning solution was prepared by mixing 500 kg of tap water with 40 kg of sodium hydroxide dissolved in it and 500 kg of methanol.
Washing was performed by circulating at 30°C for 3 hours. As a result of cleaning, the voltage per pair of electrodialyzers became 0.7V, which returned to the initial state, and there was no performance deterioration such as a decrease in current efficiency or a decrease in the mechanical strength or ion permselectivity of the ion exchange membrane. It wasn't recognized. Example 2 In the same manner as in Example 1, the ion exchange membrane with increased electrical resistance due to adhesion of organic matter was taken out by dismantling the electrodialysis tank and mixed with 500 ml of tap water and ethanol in which 130 g of sodium nitrate and 56 g of potassium hydroxide had been dissolved. 500
ml of the mixed solution for 2.0 hours at 30°C, and the AC resistance of the ion exchange membrane before and after immersion was measured. The results are shown in Tables 1 and 2. Comparative Examples 1 to 3 Instead of the cleaning solution in Example 2, 500 ml of tap water in which 130 g of sodium nitrate was dissolved and 500 ml of ethanol were mixed (Comparative Example 1): 500 ml of tap water in which 56 g of potassium hydroxide was dissolved and ethanol.
In the same manner as in Example 2, the ion exchange membrane extracted from the electrodialysis tank was immersed in tap water 1 (Comparative Example 3) in which 500 ml of the solution was mixed (Comparative Example 2): 260 g of sodium nitrate and 80 g of sodium hydroxide were dissolved. The results are shown in Tables 1 and 2.

【table】

[Table] Example 3 An electrodialysis tank in which organic matter adhered to the ion exchange membrane and the dialysis voltage increased in the same manner as in Example 1 was replaced with the cleaning solution of Example 1 using tap water in which 120 kg of sodium acetate and 40 kg of sodium hydroxide were dissolved. Water 500 and methanol
Washed at 30°C for 3 hours with a washing solution mixed with 500.
As a result, the voltage returned to its initial value. Example 4 Seawater was desalinated in the same manner as in Example 1, and the dialysis voltage was
When the voltage rose to 1.2V/v, operation of the electrodialyzer was stopped. A cleaning solution prepared by mixing 700% tap water and 300% acetone in which 160kg of potassium chloride and 80kg of potassium hydroxide were dissolved in the same manner as in Example 1 was added to the electrodialysis tank at 30°C.
It was washed by flowing for 3 hours. As a result, the voltage returned to its initial value. Example 5 When seawater was desalinated again using the battery container cleaned in Example 1, the voltage decreased again after about 50% of the seawater had been desalinated compared to when a fresh ion exchange membrane was used. It rose to 1.2V/pair. Therefore, while circulating the same cleaning solution as in Example 1,
Washing was carried out for 3 hours at a temperature of 25-30°C through a current of 125A. As a result of cleaning, the voltage per pair of battery containers is
When the seawater returns to its initial state of 0.7V/pair and is desalinated again, the amount of seawater desalted until the voltage reaches 1.2V per pair is approximately 80% of that with a fresh ion exchange membrane. increased. Example 6 In Example 5, when cleaning was carried out by changing the current direction during cleaning to the opposite of that during seawater desalination and keeping the other conditions the same as in Example 5, the battery cell voltage per pair was
When the seawater was desalinated again at 0.7V, the amount of desalination until the voltage per pair reached 1.2V/pair was almost the same as in the case of a fresh ion exchange membrane.

Claims (1)

[Claims] 1. An ion exchange membrane is brought into contact with a mixed solution of water and an organic solvent containing a sodium salt or a potassium salt of a mineral acid or a carboxylic acid, and also containing sodium hydroxide, potassium hydroxide, or ammonium hydroxide. A method for cleaning an ion exchange membrane, characterized by: 2. The method according to claim 1, wherein the organic solvent is an alcohol or a ketone. 3. The method according to claim 1, wherein the mixed solution is a mixed solution containing 5 to 80% of an organic solvent. 4. Applying electricity to a battery container equipped with an ion exchange membrane to pass a mixed solution of water and organic solvent containing sodium or potassium salts of mineral acids or carboxylic acids, and containing sodium hydroxide, potassium hydroxide, or ammonium hydroxide. A method for cleaning an ion exchange membrane, characterized by: 5. The method according to claim 4, wherein the organic solvent is an alcohol or a ketone. 6. The method according to claim 4, wherein the mixed solution contains 5 to 80% of an organic solvent. 7. The method according to claim 4, wherein the current is applied in a direction opposite to that during operation of the battery.