JP3193425B2 - Electrodialysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating an electrodialysis tank incorporating a bipolar membrane (hereinafter, also referred to as a bipolar membrane electrodialysis tank).

[0002]

2. Description of the Related Art The operation of a bipolar membrane electrodialysis tank (hereinafter, also simply referred to as an electric tank) is sometimes stopped. When such operation is stopped, the acid supplied to and discharged from the battery case,
The circulation of alkali and salt solutions is also generally stopped. At this time, the acid, alkali, and salt solution in the battery case are discharged and acid,
Most return to the alkali and salt solution tanks, but some remain in the battery case. If such a state continues, when the acid, alkali or salt solution at the bottom of the battery container stays, the bipolar membrane swells and blisters of water bubbles are generated. Once blisters are generated in such a bipolar membrane, the battery voltage increases in the next re-operation, and the flow of acid, alkali, and salt solutions deteriorates, and eventually, normal operation of the battery case becomes difficult.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to
An object of the present invention is to provide an operation method that does not generate blisters even when operation and suspension are repeated.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have found and provided a simple method that does not cause blisters in a bipolar membrane electrodialysis tank.

[0005] That is, the present invention provides an electrodialysis method characterized by washing the bipolar membrane with water when the operation of the electrodialysis tank incorporating the bipolar membrane is stopped.

The bipolar membrane referred to in the present invention is a composite ion exchange membrane having a structure in which a cation exchange membrane and an anion exchange membrane are laminated. As such a bipolar film, a known film can be used without any particular limitation. The following are known as the manufacturing method and the film. For example, a method in which a cation exchange membrane and an anion exchange membrane are bonded and cured with a mixture of polyethyleneimine-epichlorohydrin (Japanese Patent Publication No. 32-3962), and an ion exchange adhesive is used to bond the cation exchange membrane and the anion exchange membrane. (Japanese Patent Publication No. 34-3961), the cation exchange membrane and the anion exchange membrane are finely powdered ion exchange resin,
A method of applying a paste-like mixture of an anion or cation exchange resin and a thermoplastic substance and pressing the mixture (Japanese Patent Publication No. 35-145).
No. 31), a method in which a paste-like substance composed of vinylpyridine and an epoxy compound is applied to the surface of a cation exchange membrane and irradiated with radiation (Japanese Patent Publication No. 38-1).
No. 6633), a method in which a sulfonic acid type polymer electrolyte and an allylamine are attached to the surface of an anion exchange membrane and then irradiated with ionizing radiation to crosslink (Japanese Patent Publication No. 51-4113).
), A method of depositing a mixture of a base polymer and a dispersion of an ion-exchange resin having an opposite charge on the surface of an ion-exchange membrane (JP-A-53-37190), and impregnating and polymerizing a polyethylene film with styrene and divinylbenzene. A sheet is sandwiched between stainless steel frames, one side is sulfonated, the sheet is removed, and the remaining portion is chlormethylated and then aminated (US Pat.
562139), and a bipolar membrane in which the interface between an anion exchange membrane and a cation exchange membrane is treated with an inorganic compound and both membranes are joined (Japanese Patent Application Laid-Open No. 59-47235).

[0007] As the electrodialysis tank incorporating the bipolar membrane, any known electrodialysis tank can be used without any limitation. Basically, there are a two-chamber type and a three-chamber type as a bipolar membrane electrodialysis tank (Japanese Patent Publication No. 32-3962, Japanese Patent Publication No. 33-2).
023). The two-chamber type is a combination of a bipolar membrane and a cation exchange membrane or a bipolar membrane and an anion exchange membrane as a membrane, and comprises an alkali chamber and an acid / salt mixing chamber, or an acid chamber and a salt / alkali mixing chamber as a chamber. I do. The three-chamber system uses three types of membranes, a bipolar membrane, an anion exchange membrane and a cation exchange membrane, and comprises three chambers of an alkali, an acid and a salt. The bipolar membrane is usually used with the anion exchanger side facing the anode side and the cation exchanger side facing the cathode side.

Water or an aqueous solution is used for washing in the present invention. For example, any water may be used as long as the pH is 1 to 10 in ion-exchanged water, ordinary tap water, and an aqueous solution containing a soluble salt. Examples of the salt include sodium chloride, potassium chloride, lithium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, sodium nitrate, and potassium nitrate.

[0009] The water washing method of the present invention is not particularly limited as long as the bipolar membrane is washed with water. Generally, when the operation of the bipolar membrane battery is stopped, the solution is extracted from the acid chamber and the alkaline chamber of the battery vessel. The inside of the battery case may be washed with water. In general, a method is preferably used in which tap water is passed through the battery case, the tap water is removed, and then 1-10% saline is supplied and circulated again into the battery case. At this time, the pH of the circulating saline solution
It is important to adjust to be in the range of 1 to 10. Alternatively, the pH of the solution may be adjusted by circulating the aqueous solution of the salt in the battery container from the beginning.

In the present invention, it is very important to wash the alkaline chamber (anode side) and the acid chamber (cathode side) with an alkaline solution and an acid solution in the alkaline chamber (anode side) and the acid chamber (cathode side), respectively, when the battery case is stopped. . In addition, when the bipolar membrane battery is stopped, the pH of the salt chamber is usually offset to the acid side or the alkali side, so that the pH of the salt chamber is reduced by washing with water.
It is also very important to adjust H to the neutral range.

[0011]

According to the present invention, the acid and alkali in contact with the bipolar membrane are removed by stopping the operation of the bipolar membrane electrolyzer and washing the inside of the electrolyzer with water when the electrodialysis tank is stopped, and furthermore, the anion and cation exchange of the bipolar membrane. By changing the membrane portion from a hydroxyl ion or proton type to another anion / cation type, blisters are not generated and long-term operation of the electrodialysis tank is enabled.

[0012]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to these examples.

Example 1 A bipolar membrane was obtained as follows. That is, 50 parts of vinylbenzyl chloride, 35 parts of styrene, 15 parts of divinylbenzene having a purity of 50%, and benzoyl peroxide 2
Part, styrene oxide 2 parts and acrylonitrile-
A viscous polymer solution consisting of 5 parts of butadiene rubber was prepared. The polymer solution was heated and polymerized at 70 ° C. for 16 hours in a nitrogen atmosphere between glass plates to obtain a polymer film. Next, this polymer film was immersed in 96% sulfuric acid at 60 degrees for 10 minutes to introduce sulfonic acid groups on the surface of the film. Furthermore, it was placed in a mixed solution of trimethylamine-acetone-water (1: 1: 8) and treated at 30 ° C. for 1 day to introduce an anion exchange group into the inside of the membrane to obtain an anion exchange membrane. A mixture consisting of equal amounts of 5% polyvinyl alcohol and 5% glutaraldehyde is applied between the anion exchange membrane whose surface is sulfonated and the cation exchange membrane (CM-1) manufactured by Tokuyama Soda Co., Ltd., and heated at 50 ° C. Pressing was carried out for 1 hour, and bonding was performed to obtain a bipolar film. The cation exchange membrane is a cation exchange membrane (CM) manufactured by Tokuyama Soda Co., Ltd.
-1) was used.

[0014] Sodium sulfate was dissolved in ion-exchanged water to obtain 10 liters of a solution (containing 234 g of sodium sulfate). 10 liters of the resulting solution was subjected to bipolar membrane electrodialysis. As shown in FIG. 1, the bipolar membrane electrodialysis tank has 11 and 10 cation exchange membranes and 10 bipolar membranes, respectively, between a pair of negative electrodes (the effective membrane area of the cation exchange membrane and the bipolar membrane is Also 1dm ² ,
The total membrane area is 10 dm ² ), respectively, and a filter press type bipolar membrane electrodialysis tank having an alkali chamber and a mixing chamber for salt and acid is used. The 10 liter sodium sulfate solution is placed in the mixing chamber for salt and acid. Was supplied and circulated to the alkali chamber at a linear speed of 6 cm / sec with 10 liters of a 0.4% aqueous sodium hydroxide solution. The anode compartment and the cathode compartment each contain 5 liters of sodium sulfate aqueous solution (4
90 g of sodium sulfate). 40 ° C,
Electrodialysis was performed at a current density of 10 A / dm ² . As a result, 12 liters of an aqueous sodium hydroxide solution (including 700 g of sodium hydroxide) was discharged from the alkali chamber, and 808 g of sulfuric acid and 11 liters of sodium sulfate were discharged from the mixing room of acid and salt.
An 8 liter solution containing 72 g was obtained. At this time, the power consumption unit of caustic soda is 1200 kwh / t-N
aOH.

After this batch type electrodialysis operation, the alkali, acid and salt mixed solution in the battery tank is extracted, and each chamber in the tank is washed three times with 10 liters of ion-exchanged water instead. 10 liters of saline was internally circulated through each chamber. At this time, the pH of the saline solution was 4. This batch-type electrodialysis operation and aqueous solution washing were repeated 20 times in the same battery case, but no blister was found on the bipolar membrane.

Comparative Example 1 Using the same membrane and battery case as in Example 1, the inside of the battery case after the electrodialysis operation was left without being washed with water and saline, and the electrodialysis operation was repeated again. After rising, the voltage was doubled in the tenth operation, and blisters were generated on the bipolar membrane when the battery case was disassembled.

Example 2 As shown in FIG. 2, a three-chamber bipolar method comprising an anion exchange membrane (AM-1) manufactured by Tokuyama Soda Co., Ltd. in addition to the bipolar membrane and cation exchange membrane (CM-1) used in Example 1. A membrane electrodialysis tank was assembled, and a saline solution was passed as follows.

As shown in FIG. 2, the bipolar membrane electrodialysis tank has a cation exchange membrane 11, a bipolar membrane 10 and an anion exchange membrane 18 between a pair of anodes and anodes, respectively.
1 sheet, 10 sheets, 10 sheets (effective membrane area of cation exchange membrane, bipolar membrane, anion exchange membrane is 1 dm ² ,
The total membrane area is 10 dm ² ), and a filter press type bipolar membrane electrodialysis tank having an alkali chamber 12, an acid chamber 19 and a salt chamber 20 is used.
16 liters of a 5% hydrochloric acid aqueous solution, 10 liters of a 23.4% sodium chloride solution in the salt chamber, and 0.1 liter in the alkali chamber.
10 liters of 4% aqueous sodium hydroxide
The liquid was supplied and circulated at a linear speed of cm / sec. The anode compartment and the cathode compartment were each 5 liters of sodium sulfate aqueous solution (490
g of sodium sulfate). Electrodialysis was performed at 40 ° C. and a current density of 10 A / dm ² for 6 hours.

As a result, 12 liters of aqueous sodium hydroxide solution (containing 756 g of sodium hydroxide) from the alkaline chamber, 17 liters of hydrochloric acid aqueous solution (including 733 g of hydrochloric acid) from the acid chamber, and 129 g of sodium chloride from the salt chamber.
7 liters of solution containing 3 g were obtained. After this batch-type electrodialysis operation, the alkali, acid, and salt solutions in the battery case were extracted, and each chamber in the battery case was washed three times with 10 liters of ion-exchanged water instead. At this time, the pH of the base chamber solution, the acid chamber solution, and the salt chamber solution were 11, 11, respectively.
2,5. This batch-type electrodialysis operation and water washing were repeated 20 times, but no increase in voltage or generation of blisters was observed.

Comparative Example 2 Using the same membrane and battery case as in Example 2, the inside of the battery case after the electrodialysis operation was left without washing with ion-exchanged water, and when the electrodialysis operation was repeated again, the voltage gradually increased. However, in the sixth operation, the voltage was doubled from the initial value, and blisters were generated on the bipolar membrane when the battery case was disassembled.

[Brief description of the drawings]

FIG. 1 is a schematic view of a two-chamber electrodialysis tank.

FIG. 2 is a schematic diagram of a three-chamber electrodialysis tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Bipolar membrane (B) 11 Cation exchange membrane (C) 12 Alkaline chamber 13 Mixed solution chamber of acid and salt 14 Anode 15 Cathode 16 Anode chamber 17 Cathode chamber 18 Anion exchange membrane (A) 19 Acid chamber 20 Salt chamber

Claims (2)

(57) [Claims] 1. An electrodialysis method comprising washing the bipolar membrane with water when the operation of the electrodialysis tank incorporating the bipolar membrane is stopped. 2. An electrodialysis method comprising washing a room on the anode side and a room on the cathode side of the bipolar membrane when the operation of the electrodialysis tank incorporating the bipolar membrane is stopped.