JPS6235817B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for cleaning contaminated ion exchange membranes without deteriorating membrane performance. For example, if an electrodialysis device that uses an ion exchange membrane is used to desalinate or concentrate seawater over a long period of time, dissolved substances, suspended solids, microorganisms, etc. and contaminates the ion exchange membrane. If dialysis operation is continued with the ion exchange membrane contaminated, the membrane will become clogged and the electrical resistance will increase, resulting in a significant decrease in dialysis efficiency. In order to avoid such adverse effects, contaminated ion exchange membranes are cleaned, and physical cleaning methods and chemical cleaning methods are known as methods for cleaning the contaminated ion exchange membranes. A typical physical cleaning method is to dismantle the electrodialyzer, take out the ion exchange membranes, and scrub them one by one with a sponge or the like to remove deposits on the membrane surface and clean it. However, this method not only requires time and effort to disassemble and assemble the device, but also does not have a sufficient cleaning effect. On the other hand, the chemical cleaning method is a method in which deposits on the membrane surface are cleaned by immersing the ion exchange membrane in a cleaning solution, which will be described later, or by circulating the cleaning solution within the device. This chemical cleaning method is convenient in that it can be cleaned without disassembling the device, and for this reason, various proposals have been made regarding the types of cleaning agent liquid. For example, JP-A-53-65281 describes that an anion exchange membrane contaminated with organic matter is brought into contact with a solution containing an oxidizing agent such as a halogen-containing oxidizing agent or hydrogen peroxide. However, even with this method,
Although the cleaning effect can be seen to some extent, the drawback is that the ion exchange membrane is susceptible to deterioration by oxidizing agents. Particularly when cleaning the device in an assembled state, if a cation exchange membrane is installed that provides selective permeability between two or more types of cations, the selective permeability of this cation exchange membrane The disadvantage is that the performance is significantly reduced. Furthermore, JP-A No. 53-73483 describes that a combination of hydrazine and hydrogen peroxide or a hydrogen peroxide generator is applied to a contaminated ion exchange membrane in the presence of a surfactant solution. There is. In this method, it is essential to use three components: surfactant, hydrazine, and hydrogen peroxide (or hydrogen peroxide generator). A two-component system (hydrogen generating agent) has almost no cleaning effect. Although a satisfactory cleaning effect can be achieved by using the above three components, it goes without saying that it is better to use fewer types of chemicals in terms of operation and cost. Also, it has recently been announced in the press that hydrogen peroxide is a carcinogenic substance, so the use of such a drug is undesirable. In view of these points, the present inventors conducted various studies on cleaning agents that have a cleaning effect without causing deterioration of ion exchange membranes, particularly specific permselective cation exchange membranes, and found that surfactants and hypohalite salts We have discovered a cleaning agent consisting of a novel combination of the following, and have completed the present invention. The present invention is a method for cleaning an ion exchange membrane, which comprises cleaning a contaminated specific permselective cation exchange membrane with an aqueous solution containing a surfactant and a hypohalite salt. The ion exchange membrane to be cleaned in the present invention is a contaminated ion exchange membrane, and its type is not particularly limited, and it may be any type of cation exchange membrane or anion exchange membrane. In particular, there is a strong tendency to deteriorate significantly due to peroxide treatment.
Even a so-called selectively permselective ion exchange membrane that exhibits permselectivity between ions of the same type with different charges can be cleaned without causing any deterioration. Therefore, in the present invention, a specific permselective cation exchange membrane is particularly effective. Hitherto, no cleaning agent has been known that has a cleaning effect without deteriorating the performance of specific permselective cation exchange membranes. In this respect, the present invention is particularly significant. In addition, as a manufacturing method of a normal ion exchange membrane, for example, Japanese Patent Publications No. 39-19542, No. 39-27861, No. 40-
No. 28951, No. 44-19253, etc., and methods for producing specific permselective ion exchange membranes include, for example, Japanese Patent Publication Nos. 46-23607 and 47-3081 as cation exchange membranes.
47-3801, 47-3802, 50-4638, 47-3802, 50-4638,
There are No. 53-43909, No. 54-11800, No. 54-17713, etc., and as an anion exchange membrane,
No. 19980, No. 45-30693, No. 48-34676, No. 51
-28275 etc. The surfactant that is one component of the cleaning agent used in the present invention may be one or two of the known anionic surfactants, nonionic surfactants, amphoteric surfactants, or cationic surfactants. Any combination of more than one species can be used. Examples of anionic surfactants include sodium alkylbenzene sulfonate, sodium higher alcohol sulfate,
Sodium alkyl sulfonate, sodium alkyl sulfate, sodium alkylnaphthalene sulfonate-formalin condensate, sodium alkylnaphthalene sulfonate, sodium polystyrene sulfonate, sodium polyacrylate, sodium polymethacrylate, etc.; as nonionic surfactants Examples of amphoteric surfactants include polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyethylene glycol fatty acid ester, and polyacrylamide; examples of amphoteric surfactants include betaine type and imidazoline type; and cationic surfactants. as,
Alkylpyridinium hydrochloride, alkyltrimethylammonium halide, polyoxyethylenealkylamine, polyethyleneimine, poly-4-
Alkylated vinylpyridine, polyvinyltrimethylbenzylammonium chloride, etc. are used. Among these surfactants, the molecular weight is between 200 and 5000.
It is preferable to use In addition, surfactants are generally 50ppm to 50ppm.
It is used as an aqueous solution with a concentration of 10000 ppm, preferably 100 ppm to 8000 ppm. If the concentration of the surfactant is less than 50 ppm, the cleaning effect of the ion exchange membrane will be insufficient, and if it is more than 10,000 ppm, the cleaning effect will not improve and it will be uneconomical. Examples of the hypohalite which is another component of the cleaning agent of the present invention include aqueous solutions of halogen elements such as chlorine and bromine, sodium hypochlorite, calcium hypochlorite, potassium hypochlorite, There are sodium hypobromite, calcium hypobromite, etc., and these are used alone or as a mixture in an aqueous solution. Hypohalites generally have an effective halogen concentration of 1 ppm to 1000 ppm, preferably 10 to 1000 ppm.
Used at a concentration of 800ppm. If it is less than 1 ppm, the cleaning efficiency is low, and if it is more than 1000 ppm, the specific permselectivity between similar ions may be lost in the case of a membrane with specific permselectivity. In the present invention, an aqueous solution of a surfactant and an aqueous solution of a hypohalite salt may be used as a mixture, or each may be used alone. When used alone, it is necessary to use a surfactant solution first; on the other hand, it is not preferable to use an aqueous solution of hypohalite salt first because it causes deterioration of the ion exchange membrane. When a mixed solution is used, it is preferable that the pH thereof is 10 times or more higher than the stability of the hypohalite salt. Incidentally, inorganic salts such as sodium chloride and sodium sulfate, water-soluble organic substances such as alcohol and sugars, etc. may coexist in the mixed liquid as a third component. In the present invention, methods for cleaning contaminated ion exchange membranes include two methods: removing the ion exchange membrane from the device and cleaning only the membrane, and a method of cleaning by circulating a cleaning agent solution within the device without disassembling the device. There is a way. Methods for cleaning only the ion exchange membrane include a method in which the ion exchange membrane is immersed in a surfactant solution, then a hypohalite solution is added and mixed, and the mixture is left standing or stirred for cleaning; There are methods such as immersion in a mixed solution of an activator and a hypohalite salt. In addition, as a method for circulating the cleaning solution within the device, first circulate a surfactant solution, add hypohalite to it to a predetermined concentration, make a mixed solution, and circulate it. There are two methods: a continuous method, a method of circulating a mixed solution of surfactant and hypohalite, etc. It is desirable to carry out so-called bubble agitation in which bubbles of air or nitrogen are blown during the circulation within the apparatus. Among these methods, circulating a mixed solution of surfactant and hypohalite in the assembled state of the device is not only simple, but also the material used to construct the device. This method is preferably adopted because it has the advantage of being able to clean contaminants deposited on spacers, dilution chamber frames, concentration chamber frames, distribution plates, pipes, etc. The cleaning temperature in the present invention is generally 0°C to 50°C.
℃, preferably in the range of 5℃ to 40℃. The cleaning time varies depending on the degree of contamination of the ion exchange membrane, the cleaning method, etc., but is generally 0.5 to 30 hours. As described above, according to the present invention, by cleaning the ion exchange membrane in a two-component aqueous solution of a surfactant and a hypohalite, it is not only possible to completely clean and remove contaminants deposited on the ion exchange membrane, but also to No deterioration in the performance of the ion exchange membrane was observed. Even in the case of specific permselective ion exchange membranes, there is no loss at all. It goes without saying that the cleaning method of the present invention can be applied not only to ion exchange membranes contaminated by electrodialysis, but also to membranes contaminated by diffusion dialysis, electrolytic reactions, and the like. Although the excellent cleaning action mechanism of the present invention is not clear, its effects will be made clear by the Examples described below. EXAMPLES Hereinafter, the present invention will be explained in more detail 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 alternately installed with rubber chamber frames and spacers made of Netron. Seawater with the composition shown in the table below is flowed into the dilution chamber of the dialysis tank at a flow rate of 6 cm/sec, and the water is measured against the membrane area through electrodes installed at both ends.
A current is passed at a current density of 3.5A/ ^dm2 . The effective area of the ion exchange 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 To evaluate the permselectivity of the anion exchange membrane, the permselectivity coefficient (P ^SO4 _Cl was determined by the following formula. P ^SO4 _Cl = [ _SO4 ]/[Cl]×0.53/0
．． 05 (However, [Na], [K], [Cl], and [SO ₄ ] represent the respective concentrations of Na, K, Cl, and SO ₄ in the concentrate.) Example 1 Polyethyleneimine with a molecular weight of about 1000 A cation exchange membrane Neocepta CH-45T manufactured by Tokuyama Soda Co., Ltd. was immersed in a 500 ppm aqueous solution at 20C for 10 hours, and then immersed in a hydrochloric acid/formalin mixture for 20 hours to crosslink polyethyleneimine with formalin. This selectively permeable cation exchange membrane and a large number of selectively permeable anion exchange membrane Neosepta ACS manufactured by Tokuyama Soda Co., Ltd. were installed alternately, and seawater concentration was carried out for three months. During this period, suspended matter in the seawater adhered to the ion exchange membrane surface and spacer flow plate, causing the dialysis tank inlet pressure to drop from 0.5Kg/ ^cm2.
The weight rose to 1.1 kg/cm ² and it became difficult to continue electrodialysis. First, the concentration of sodium dodecylbenzenesulfonate
A 1000 ppm aqueous solution was circulated in the dilution chamber of the electrodialysis tank for 1 hour, and then sodium hypochlorite and caustic soda were gradually added to this solution, so that the sodium hypochlorite (available chlorine concentration) was 100 ppm and the pH of the solution was 11.0. did. This mixed solution of PH = 11.0 was circulated for 3 hours,
Washed. As a result of cleaning, the inlet pressure of the dialysis tank is 0.5 again.
Kg/ ^cm2 . As a result of dismantling the electrodialysis tank, the deposits from before cleaning were completely removed. When electrodialysis was performed after washing, no voltage increase was observed. The pure salt percentage and the selective permeability coefficient of the anion exchange membrane were as shown in Table 1.

[Table] The values after washing were unchanged from the initial values, and no deterioration of the specific permselectivity cation (anion) ion exchange membrane had occurred. Comparative Example 1 The same treatment as in Example 1 was carried out using a cleaning agent obtained by removing sodium dodecylbenzenesulfonate from the mixed solution. After washing, electrodialysis was performed and the inlet pressure of the dialysis chamber was 0.6 Kg/cm ² . Recovery was not as great as in Example 1. In addition, the pure salt rate is 81.0%,
The specific permselective cation exchange membrane had deteriorated. Example 2 90 parts of styrene, 10 parts of divinylbenzene of 50% purity
A paste-like mixture consisting of 20 parts of polyvinyl chloride fine powder, 20 parts of dioctyl phthalate, and 1 part of benzoyl peroxide was applied to a polyvinyl chloride cloth, and the polymer film was heated and polymerized using cation exchange. Used as a membrane membrane. Next, this raw film was mixed with chlorosulfonic acid:sulfuric acid=
It was immersed in a 1:1 mixed solution at 40°C for 30 minutes to introduce sulfonyl chloride groups into the phenyl groups in the raw film. Next, this film-like material was immersed in a 5% polyethyleneimine aqueous solution for 16 hours to allow the sulfonyl chloride groups on the surface of the raw film to react with the polyethyleneimine, and then
Soaked in 1N-caustic soda aqueous solution at room temperature for 8 hours,
Internal unreacted sulfonyl chloride groups were converted to sodium sulfonate. This is a specific permselective cation exchange membrane. As in Example 1, the above specific permselective cation exchange membrane and Neocepta ACS were used.
Seawater concentration was performed using a combination of The dialysis tank inlet pressure is
Initially 0.5Kg/ ^cm2 , when it became 1.2Kg/ ^cm2 , sodium hypochlorite 100ppm, amphitol 24B (lauryl betaine, manufactured by Kao Soap Co., Ltd.)
The inside of the dialysis tank was cleaned for 6 hours with a mixed cleaning solution of 300 ppm and pH 10.0. The dialyzer inlet pressure was restored to 0.5Kg/cm ² . The pure salt rate and selective permeability coefficient were as shown in Table 2.

[Table] The values after washing were the same as the initial values. Comparative Example 2 The same treatment as in Example 2 was carried out using an aqueous solution containing 0.1% of sodium percarbonate and 0.2% of the surfactant polyoxyethylene lalaryl ether as a cleaning agent. As a result of electrodialysis after washing, the dialysis chamber pressure was
Although it recovered to its original value of 0.5 Kg/cm ² , the pure salt ratio selective permeability coefficient became as shown in Table 3, and as is clear from the values in the pure salt ratio column, the monovalent ion permselectivity decreased.

[Table] Examples 3, 4, 5 The same anion and cation exchange membranes as in Example 2 to which floating matter in seawater was attached were washed with the cleaning solution shown in Table 4 at 25°C for 10
Washed for hours.

[Table] Emulgen 120 (polyoxyethylene lauryl ether), Cortamine 24P (lauryl trimethyl ammonium chloride), and Demol N (naphthalene sulfonic acid formalin condensate) are manufactured by Kao Soap Co., Ltd. The deposits were completely removed by washing. The electrical resistance of the anion and cation exchange membranes after washing was the same as that of the unused membranes in Examples 3, 4, and 5.

Claims (1)

[Scope of Claims] 1. A method for cleaning an ion exchange membrane, which comprises cleaning a contaminated specific permselective cation exchange membrane with an aqueous solution containing a surfactant and a hypohalite. 2. The cleaning method according to claim 1, wherein the concentration of the surfactant is 100 to 8000 ppm. 3. The cleaning method according to claim 1, wherein the concentration of hypohalite is 10 to 800 ppm in terms of effective halogen concentration. 4. The cleaning method according to claim 1, wherein the ion exchange membrane is a specific permselective cation exchange membrane or anion exchange membrane. 5. The cleaning method according to claim 1, wherein the aqueous solution containing a surfactant and a hypohalite has a pH of 10 to 13.