JPS6240062B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for regenerating a cation exchange membrane with reduced permselectivity. Traditionally, normal cation exchange membranes have been studied as ones that selectively permeate only cations, but when electrodialyzing an electrolyte solution containing two or more types of cations (for example, electrodialyzing seawater), A cation exchange membrane with excellent specific permselectivity between two or more types of cations is manufactured from the viewpoint of preventing the formation of scales such as gypsum and improving the current efficiency of sodium ions when concentrating salt to produce salt. I have reached the point where When electrodialysis is continued using a selectively treated cation exchange membrane, the persistence (durability) of permselectivity differs depending on the type of cation exchange membrane.
In addition, electrodialysis conditions such as current density, temperature, concentration, and composition of the dialysate, and seawater concentration may vary depending on the type and content of suspended solids such as microorganisms, algae, and plankton in the raw seawater. There are also differences in the persistence of selective permeability depending on the difference. However, in any case, the permselectivity of the cation exchange membrane decreases with the passage of dialysis time, so it has been necessary to regenerate it by some method. Nevertheless, no industrially satisfactory method has been established. The present inventors have conducted extensive research into industrial methods for regenerating cation exchange membranes with reduced permselectivity, and have found that pretreatment of the cation exchange membranes with a specific treatment aqueous solution results in subsequent selectivity. We have completed the present invention by discovering that the treatment is significantly improved and the regeneration effect is comparable to that of a cation exchange membrane that has undergone a new permselective treatment. That is, in the present invention, when regenerating a cation exchange membrane that has been subjected to permselective treatment, the cation exchange membrane is (i) brought into contact with an aqueous solution containing an oxidizing agent and/or (ii) brought into contact with an acidic aqueous solution, and then This is a method for regenerating a cation exchange membrane with reduced permselectivity, in which the cation exchange membrane is pretreated by contacting with an aqueous alkaline solution and then subjected to a selective treatment. The permselectivity-treated cation exchange membrane used in the present invention is not particularly limited as long as it has been treated to impart permselectivity (hereinafter also simply referred to as specific permselectivity) between two or more types of cations. Can be used. Various methods are known for producing specific permselective cation exchange membranes, such as Japanese Patent Publication No. 46-23607, No. 46-42082,
No. 46-42083, No. 47-3081, No. 47-3802,
There is No. 48-34676, etc. Further, the cation exchange membrane in the present invention can be used without being limited to polymerization type, condensation type, uniform type, non-uniform type, presence or absence of a reinforcing core material, etc. 1 of the pretreatment agents for the cation exchange membrane in the present invention
The seed oxidizing agent is not particularly limited, and any known oxidizing agent can be used. Specific examples of suitable oxidizing agents include aqueous solutions containing halogens such as chlorine and bromine; aqueous solutions containing halogenated salts such as hypohalites, halites, and perhalides; It is. Particularly industrially, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, sodium hypobromite, potassium hypobromite, etc. are used to prevent deterioration of cation exchange membranes and are easily available. Most preferred are hypohalite salts of . The concentration of oxidizing agents used varies depending on the type, and cannot be unconditionally limited, but in general, halogen elements are used in concentrations of 10 to 10
A range of 10000ppm is used. In addition to the halogen-containing aqueous solution, oxidizing agents such as hydrogen peroxide and sodium percarbonate can also be used, but in the case of hydrogen peroxide, the ion exchange groups may be destroyed if other ions coexist, so avoid using hydrogen peroxide as much as possible. It is preferable to use a thinner concentration. Usually 0.01 as hydrogen peroxide
It is preferable to use about 1 to 1% (by weight). Generally, when a cation exchange membrane is treated with a highly concentrated oxidizing agent, the ion exchange membrane itself may be degraded to varying degrees, so determine in advance the concentration that will not cause the cation exchange membrane to deteriorate depending on the type of oxidizing agent. It is preferable to use it. The acidic aqueous solution used in the present invention is a mineral acid such as hydrochloric acid,
It is preferable to use an aqueous solution of sulfuric acid, phosphoric acid, or the like.
In addition, the acid concentration of the acidic aqueous solution is not particularly limited, but
Generally, a concentration of about 0.05 to 2N is sufficient. Further, as the alkaline aqueous solution used in the present invention, caustic soda, caustic alkali, aqueous ammonia, etc. are preferably used. Although the alkaline concentration of the alkaline aqueous solution is not particularly limited, it is generally sufficient to use an aqueous solution having a concentration of 0.01 to 1 normal. It is of course possible to increase the above-mentioned acid and alkali concentrations as long as they do not adversely affect the ion exchange membrane such as deterioration, but even if the concentration is increased, the effect will hardly change. Therefore, it is industrially most preferable to use an aqueous solution having the above-mentioned acid and alkali concentrations. The treatment time of the aqueous solution treatment containing an oxidizing agent, acidic aqueous solution treatment, and alkaline aqueous solution treatment of the present invention varies depending on the concentration of each aqueous solution, treatment conditions, etc., and cannot be absolutely limited, but is generally preferably 0.5 to 4 hours. Further, the treatment temperature is generally preferably 10 to 50° C. as well as the treatment time. As described above, the present invention is characterized in that, when regenerating a cation exchange membrane subjected to permselectivity treatment, at least one of the following treatments (i) and (ii) is performed as a pretreatment of the membrane. This is a method for regenerating a cation exchange membrane with reduced permselectivity. (i) Contact with an aqueous solution containing an oxidizing agent. (ii) Contact with an acidic aqueous solution and then an alkaline aqueous solution. Aqueous solution, acidic aqueous solution, alkaline aqueous solution (hereinafter also simply referred to as treatment liquid) containing an oxidizing agent in the present invention
When processing, stop the operation of the electrodialysis tank,
The above-mentioned treatment liquid may be supplied to the electrodialysis tank through the ducts and slots that have conventionally supplied dialysate to the electrodialysis tank, or, of course, the ion exchange membrane can be disassembled and removed from the electrodialysis tank and immersed in the treatment liquid. It can also be implemented by The mechanism of action of how the treatment liquid in the present invention acts on a cation exchange membrane with degraded permselectivity and contributes to the selective treatment described below is not clear. However, as will be clear from the examples described below, by implementing the present invention, the recovery rate of the performance of the ion exchange membrane is almost 100%, which is of great industrial significance. In the present invention, it is necessary to subject the cation exchange membrane that has undergone the above pretreatment to a selective treatment. The selection process is not particularly limited, and any known technique may be used as is. The following are examples of typical methods for the selection treatment that are used industrially. For example, the cation exchange membrane that has been pretreated as described above is added to a high molecular weight amine solution, such as amines with a molecular weight of 100 or more, specifically laurylamine, laurylmethylamine, phenylenediamine, polyvinylpyridine, polyvinylimidazole, polyethyleneimine, etc. A method of contacting with a solution of can be suitably used. In particular, a method of immersing the cation exchange membrane in an amine solution between the negative and positive electrodes and electrophoretically adhering the amine to the ion exchange membrane while applying electricity is industrially suitable. The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples. In the following examples, seawater was concentrated using a multichamber dialysis tank in which cation exchange membranes and anion exchange membranes were installed alternately with rubber chamber frames and spacers made of Netron. Flow seawater with the composition shown in the table below into the dilution chamber of the dialysis tank at a flow rate of 6 cm/sec.
The membrane area is measured through electrodes installed at both ends of the membrane.
A current is passed at a current density of 3.5A/ ^dm2 . The effective area of the membrane is 2 dm ² and the seawater temperature is 30°C.

[Table] To evaluate the permselectivity of the cation exchange membrane, the pure salt percentage was determined by the following formula after energization. Pure salt rate = [Na] + [K] / [Cl] × 100 (However, [Na], [K], [Cl] are Na in the concentrate,
The anion exchange membrane used in the examples was a selectively permeable anion exchange membrane [Neosecepta A3VS-8T (trade name of Tokuyama Soda)]. Example 1 1 part of polyvinyl chloride fine powder, 6 parts of styrene, 0.6 part of divinylbenzene, 2 parts of dioctyl phthalate
After uniformly mixing 0.1 part of benzoyl peroxide and applying it to a polyvinyl chloride cloth,
The film obtained by heating polymerization at ℃ for 3 hours is heated to 40℃.
A cation exchange membrane (unselected membrane) is obtained by treating with sulfuric acid:chlorosulfonic acid (1:1) for 30 minutes. The obtained cation exchange membrane was incorporated into a dialysis tank.
After a 500 ppm polyethyleneimine aqueous solution was supplied to the dilution chamber at a flow rate of 2 cm/sec for 4 hours for selective treatment, the seawater was concentrated using the cation exchange membrane, and the initial pure salt percentage was 94%. It was hot. After continuous operation for a long period of time and when the pure salt rate drops to 86%, the operation is stopped, the dialysis tank is disassembled, the ion exchange membrane is taken out, the membrane surface is wiped clean with a sponge scrubber, and the dialysis tank is reinstalled. The processing solution was supplied to the dilution chamber at a flow rate of 2 cm/sec using the processing method shown in Table 1. No. 1 to No. 5 are comparative examples. (a) in the table,
(B) and (C) mean that the processing was performed in this order, and the same applies to the following examples. Above No.
After the treatment of No. 1 to No. 16, a 500 ppm polyethyleneimine aqueous solution was supplied to the dilution chamber at a flow rate of 2 cm/sec for 4 hours to carry out selection treatment and start operation. The pure salt ratio after operation was as shown in the right column of Table 1.

【table】

[Table] Example 2 The unselected cation exchange membrane used in Example 1 was incorporated into a dialysis tank, and a 300 ppm polyethyleneimine aqueous solution was supplied to the dilution chamber at a flow rate of 2 cm/sec for 4 hours, and then the seawater was concentrated. I went. When concentrating seawater, an aqueous solution of dicyandiamide and formaldehyde polycondensate was added to the supplied seawater for 4 hours each day to a concentration of 0.1 ppm. The initial pure salt rate is
It was 92%, then rose to 95%, and then declined over time. After 8 months of operation, pure salt rate is 86%
When the temperature reaches 100, stop operation, and without dismantling the dialysis tank, use the treatment method shown in Table 2 to put 2
The processing solution was supplied at a flow rate of cm/sec. No. 1 to No. 3 are comparative examples. After processing No. 1 to No. 8 above, each
A 300 ppm polyethyleneimine aqueous solution was supplied to the dilution chamber at a flow rate of 2 cm/sec for 4 hours to carry out selectivity treatment and operation was started. The pure salt ratio after the operation was approximately as shown in the right column of Table 2.

【table】

[Table] Example 3 The same procedure as in Example 1 was carried out except that a 1% aqueous sodium percarbonate solution was used instead of the treatment agent in Example 1, and the treatment time was changed to 2 hours and 30 minutes. As a result, the pure salt rate was 93%.

Claims (1)

[Claims] 1. A selection characterized in that when regenerating a cation exchange membrane subjected to permselectivity treatment, at least one of the following treatments (i) and (ii) is performed as a pretreatment of the membrane. A method for regenerating a cation exchange membrane with reduced permeability. (i) Contact with an aqueous solution containing an oxidizing agent. (ii) Contact with an acidic aqueous solution and then an alkaline aqueous solution.