JP3151042B2 - Method for producing acid and alkali - 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 producing an acid and an alkali by performing electrodialysis of a salt solution using a bipolar membrane.

[0002]

It is known to produce acids and alkalis by electrodialysis of aqueous salt solutions using bipolar membranes. The method for electrodialysis of a salt aqueous solution using a bipolar membrane can be divided into the following two methods. One is a two-chamber cell system in which a plurality of bipolar membranes and a cation exchange membrane or an anion exchange membrane are alternately arranged.
No. -2023. The other is a three-chamber cell system in which a plurality of cation exchange membranes, bipolar membranes, and anion exchange membranes are arranged in this order. This method is disclosed in Japanese Patent Publication No. 32-3962, Japanese Patent Publication No. 33-6963, and This is known from JP-A-63-65912.

[0003] In electrodialysis using a bipolar membrane, polyvalent cations such as calcium and magnesium in a salt solution tend to permeate through a cation exchange membrane during electrodialysis. And precipitates in the cation exchange membrane, eventually destroying the cation exchange membrane. To avoid this, Japanese Patent Laid-Open
Japanese Patent Publication No. 3-65512 proposes a method of removing polyvalent cations from an aqueous salt solution and then performing electrodialysis. However, this method requires equipment for removing polyvalent cations from the aqueous salt solution and requires a large amount of funds.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an aqueous solution of an acid or an alkali which does not precipitate a hydroxide of a polyvalent cation in a cation exchange membrane even when an aqueous salt solution containing a polyvalent cation is used. It is to provide a manufacturing method.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, even when a salt aqueous solution containing a polyvalent cation is used, the polyvalent cation is not contained in the cation exchange membrane. The present inventors have found a method for preventing precipitation of a cation hydroxide, and have provided the present invention.

That is, according to the present invention, a cation exchange membrane and a bipolar membrane are alternately arranged between an anode and a cathode to form an alkali chamber and an acid / salt mixing chamber. In the method for producing an aqueous solution of an alkali and an acid / salt mixture, the pH of the aqueous solution of an acid / salt mixture in the acid / salt mixing chamber is set to 1 A method for producing an aqueous solution of a mixed alkali and acid / salt, wherein

Further, according to the present invention, a cation exchange membrane, a bipolar membrane and an anion exchange membrane are sequentially arranged between an anode and a cathode to form a salt chamber, an acid chamber and an alkali chamber, and a salt aqueous solution is formed in the salt chamber. Wherein the pH of the aqueous salt solution in the salt chamber is set to less than 1 in the method for producing an acid and an alkali. provide.

In the present invention, a known electrodialysis tank incorporating a bipolar membrane can be used without any limitation. For example, as a two-chamber type, as shown in FIG. 1, a bipolar membrane (B) and a cation exchange membrane (C) are alternately arranged between an anode 1 and a cathode 2, and an alkali chamber is interposed between the membranes. 3 and an acid / salt mixing chamber 4 are formed.

In the three-chamber type, as shown in FIG. 2, a bipolar membrane (B), an anion exchange membrane (A) and a cation exchange membrane (C) are sequentially placed between an anode 11 and a cathode 12. One having an arrangement in which three chambers of an alkali chamber 13, an acid chamber 14, and a salt chamber 15 are formed can be given. Here, a chamber between the cation exchange membrane (C) and the bipolar membrane (B) is an alkali chamber 13, a chamber between the bipolar membrane (B) and the anion exchange membrane (A) is an acid chamber 14, and an anion exchange membrane. (A)
The chamber between the water and the cation exchange membrane (C) is called a salt chamber 15.

A typical configuration of an electrodialyzer is represented by an anode- (CB) nC-cathode in the case of a two-chamber system, and an anode- (CBA-A) in the case of a three-chamber system. -) Indicated by nC-cathode. Here, the minimum repeating unit composed of a cation exchange membrane, a bipolar membrane, an anion exchange membrane and the like is referred to as a cell, and n is the number of repeating layers of the cell. Incidentally, the bipolar membrane is usually used with the anion exchanger side facing the anode side and the cation exchanger side facing the cathode side.

In the above-mentioned electrodialysis tank, as the anode and the cathode, electrodes used in the electrochemical industry such as water electrolysis and salt electrolysis are used without any limitation. For example, nickel, iron, lead, platinum or graphite can be suitably used as the anode material, and nickel, iron, stainless steel or platinum can be suitably used as the cathode material.

The type of anolyte supplied to the anode chamber can be appropriately selected according to the type of anode material. Preferred examples of these combinations are, for example, as follows. Examples include nickel or iron-sodium hydroxide aqueous solution, lead-sulfuric acid aqueous solution, platinum-sulfuric acid or sodium sulfate aqueous solution, and graphite-salt aqueous solution. Preferred combinations of the cathode material and the catholyte are as follows. Nickel, iron, or stainless steel-can include sodium hydroxide, sodium sulfate, or saline solutions.

The cation exchange membrane used in the present invention is not particularly limited, and a known cation exchange membrane can be used. For example, those having a sulfonic acid group, a carboxylic acid group, a phosphonic acid group, a sulfate ester group, and a phosphate ester group, and a cation exchange membrane in which a plurality of these ion exchange groups are mixed can be used. Cation exchange membranes can be polymerized, condensed, homogeneous, or non-uniform, and can be derived from the presence or absence of a reinforcing core, hydrocarbon-based, fluorine-based, materials or production methods. Any type and type of ion exchange membrane may be used. Furthermore, a 2N-brine solution is electrodialyzed at a current density of 5 A / dm ² , and is generally called an amphoteric ion exchange membrane if it functions as a cation exchange membrane having a current efficiency of 70% or more. Any of them can be used as the cation exchange membrane of the present invention.
Also, it is preferable to use a fluorine-based cation exchange membrane in contact with the anode chamber.

The bipolar membrane used 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 is known as a manufacturing method thereof. For example, a method of laminating a cation exchange membrane and an anion exchange membrane with a mixture of polyethyleneimine-epichlorohydrin and hardening and bonding the same (Japanese Patent Publication No. 32-3962), an ion exchange bond between the cation exchange membrane and the anion exchange membrane (Japanese Patent Publication No. 34-3961), a method in which a cation exchange membrane and an anion exchange membrane are coated with a fine powder of an ion exchange resin, or a paste mixture of an anion or cation exchange resin and a thermoplastic substance. Pressure bonding method (Japanese Patent Publication No. 35-14531), a method of applying a paste-like substance composed of vinylpyridine and an epoxy compound on the surface of a cation exchange membrane and irradiating it with a paste (Japanese Patent Publication No. 38-1983) No. 16633), ionizing radiation after adhering a sulfonic acid type polymer electrolyte and allylamine on the surface of an anion exchange membrane. Irradiation cross-linking method (Japanese Patent Publication No. 51-4113) and method of depositing a mixture of a dispersion system of an ion-exchange resin having an opposite charge and a base polymer on the surface of an ion-exchange membrane (JP-A-53-37190) ), A sheet of polyethylene film impregnated with styrene and divinylbenzene was sandwiched between stainless steel frames, one side was sulfonated, the sheet was removed, the remaining part was chloromethylated, and then aminated. (U.S. Pat. No. 3,562,139), and a method in which the interface between an anion exchange membrane and a cation exchange membrane is treated with an inorganic compound and the two membranes are joined (Japanese Patent Laid-Open No. 59-472).
No. 35).

The anion exchange membrane used in the present invention is not particularly limited, and a known anion exchange membrane can be used.
For example, an anion exchange membrane in which a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, and a plurality of these ion exchange groups are mixed can be used. The anion exchange membrane may be of a polymerization type, a condensation type, a uniform type, or a non-uniform type. In addition, the presence or absence of a reinforcing core, a hydrocarbon-based material, a fluorine-based material, and an anion derived from a material / manufacturing method. Any type and type of ion exchange membrane may be used. Further, a 2N-salt solution is subjected to electrodialysis at a current density of 5 A / dm ² and a current efficiency of 70% or more and substantially functions as an anion exchange membrane. Can be used as the anion exchange membrane of the present invention. Since an anion exchange membrane tends to easily transmit an acid, it is preferable to use an anion exchange membrane that does not easily transmit an acid.

In the present invention, the salt used as an object of electrodialysis is not limited, regardless of an organic salt and an inorganic salt, as long as the acid and alkali generated by performing salt decomposition by electrodialysis form an aqueous solution. Can be used without. Examples of the cation constituting the salt include sodium, potassium, lithium, and ammonium ions. Examples of the anions constituting the salt include halogen ions of fluorine, chlorine, bromine and iodine, sulfate ions, nitrate ions, acetate ions and lactate ions.

The method of electrodialysis in the present invention includes:
The salt chamber, the acid chamber, the alkali chamber and the acid / salt mixing chamber are provided with a liquid tank to be supplied to each chamber, and the liquid to be supplied to each chamber is circulated between each chamber and the liquid tank. Can be suitably adopted.

As a method for extracting the generated acid or alkali, the following method can be suitably employed.

1. Initially, a thin acid or alkali aqueous solution is charged to generate an acid or alkali, and when a predetermined concentration is reached, a predetermined amount of the acid or alkali is extracted and water is replenished to obtain an initial acid or alkali concentration. Batch method.

2. A continuous method in which an aqueous solution of an acid or alkali having a predetermined concentration is previously charged, and water is continuously added at the time of energization in accordance with the amount of electricity supplied, thereby causing the aqueous solution of an acid or alkali having a predetermined concentration to overflow.

The most important feature of the present invention is that the pH of the aqueous acid / salt mixture in the acid / salt mixing chamber is less than 1 in the two-chamber system,
In the case of a three-chamber system, the pH of the salt aqueous solution in the salt room is set to less than 1. In this way, even if an aqueous acid / salt mixture or an aqueous salt solution containing a polyvalent cation is supplied to the acid / salt mixing chamber or the salt chamber, the calcium and magnesium ions contained in the aqueous acid / salt mixture or the aqueous salt solution are supplied. To reach the alkaline chamber through the cation exchange membrane,
It does not form water-insoluble salts and does not damage the membrane.

Although the mechanism of permeation of multivalent cations such as calcium and magnesium through a cation exchange membrane is not always clear, the present inventors think as follows.
Polyvalent cations contained in the acid / salt mixed aqueous solution or the salt aqueous solution form a water-insoluble salt while passing through the cation exchange membrane toward the cathode. However, in the electrodialysis using a bipolar membrane, the concentration of the generated alkali is considerably lower than that of salt electrolysis, and since the temperature is low, a water-insoluble salt of a polyvalent cation that permeates the cation exchange membrane is used. Generation speed is slow. To this end, the water-insoluble salt of the polyvalent cation formed during the passage through the cation exchange membrane is dissolved in a low pH aqueous acid / salt mixture or an aqueous salt solution. It is thought that they pass through the exchange membrane and are transported to the alkaline chamber.

At present, the allowable concentration of polyvalent cations such as calcium and magnesium in a saline solution in salt electrolysis is 50 ppb or less, but according to the method of the present invention, the concentration of the polyvalent cation in the salt aqueous solution is reduced. , The electrodialysis can be continued for a long time without breaking the cation exchange membrane and without increasing the voltage. Such a phenomenon is surprising compared to salt electrolysis.

The method for adjusting the pH of the aqueous acid / salt mixture in the acid / salt mixing chamber or the aqueous salt solution in the salt chamber to less than 1 is as follows.
Usually, a method can be adopted in which an acid / salt mixed aqueous solution or an aqueous salt solution whose pH is adjusted to less than 1 by adding an acid is supplied to the acid / salt mixing chamber or the salt chamber, respectively. The acid added to make the pH less than 1 is preferably an acid having the same type of anion as the salt, but an acid having a different type of anion may be used in some cases.

If the pH of the acid / salt mixed aqueous solution or the aqueous salt solution is too low, a large amount of hydrogen ions permeate through the cation exchange membrane during electrodialysis and become water in the alkaline chamber, so that the current efficiency may be significantly reduced. . Therefore, pH
Is preferably in the range of 0 to 0.95. The pH of the aqueous acid / salt mixture in the acid / salt mixing chamber or the aqueous salt solution in the salt chamber does not always need to be lower than 1, and the acid is added intermittently to the aqueous acid / salt mixture or the aqueous salt solution. By doing so, the pH may be temporarily lower than 1. In this case, the time during which the pH occupying the entire electrodialysis time is less than 1 is preferably 20% or more.

[0026]

According to the present invention, the electrodialysis is carried out by simply producing a water-insoluble salt of a polyvalent cation by merely making the pH of the aqueous acid / salt mixture or the aqueous salt solution less than 1 to produce a water-insoluble salt of a polyvalent cation. Voltage rise can be prevented. Further, breakage of the cation exchange membrane due to generation of a water-insoluble salt of a polyvalent cation can be prevented.

[0027]

EXAMPLES The present invention will be described more specifically with reference to the following Examples and Comparative Examples, 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 dissolved in 96% sulfuric acid for 6 hours.
It was immersed at 0 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 anion exchange groups into the inside of the film to obtain an anion exchange membrane. . This surface is a sulfonated anion exchange membrane and a cation exchange membrane (trade name, CM-
During 1), a mixture consisting of an equal amount of 5% polyvinyl alcohol and 5% glutaraldehyde was applied, and heated and pressed at 50 ° C. for 1 hour to obtain a bipolar film. The cation exchange membrane used was a cation exchange membrane (trade name, CL-25T) manufactured by Tokuyama Soda Co., Ltd.

[0029] Sodium sulfate and sulfuric acid were dissolved in water to prepare a solution containing 213 g of sodium sulfate and 49 g of sulfuric acid in 1 liter. The pH of this solution was 0.90. The concentration of calcium ions in the solution was 3 ppm.

The obtained solution was subjected to bipolar membrane electrodialysis. The bipolar membrane electrodialysis tank, as shown in FIG.
Each 11 sheets and 10 sheets and a cation exchange membrane and the bipolar membrane is alternately between a pair of cathode and electrode (cation exchange membrane, both the effective membrane area of the bipolar membrane 1 dm ^2, the total membrane area, respectively 11 dm ² and 10 dm ² ), a filter press type bipolar membrane electrodialysis tank in which an alkali chamber and an acid / salt mixing chamber were formed was used.

The above-mentioned sodium sulfate-
A fixed amount of water is continuously added to the sulfuric acid mixed solution in the alkali chamber, and a 2N aqueous sodium hydroxide solution is added to each of 6 c.
The mixture was supplied and circulated at a linear velocity of m / sec, and a 2N aqueous sodium sulfate solution was circulated in each of the anode chamber and the cathode chamber.
Electrodialysis was performed at 40 ° C. and a current density of 10 A / dm ² .
As a result, the cell voltage was 1.3 volts. The power consumption of caustic soda was 1500 kwh / t-NaOH. This operation was continued for 10 days, and no increase in cell voltage was observed. No precipitate was observed in the cation exchange membrane.

COMPARATIVE EXAMPLE 1 Using the same membrane and electrodialysis tank as in Example 1, the acid / salt mixing chamber was adjusted to pH 2 with a calcium concentration of 3 ppm.
A specified aqueous sodium sulfate solution was supplied to perform electrodialysis. At this time, the cell voltage increased from 1.3 to 2.5 volts three days after the current was applied, and white precipitates were observed all over the cation exchange membrane.

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

As shown in FIG. 2, the bipolar membrane electrodialysis tank has eleven cation exchange membranes (C), bipolar membranes (B) and anion exchange membranes (A) between a pair of anodes and anodes, respectively. 10, 10 sheets (Effective membrane area of cation exchange membrane, bipolar membrane, anion exchange membrane is 1d
m ^2, the total membrane area, respectively 11dm ^2, 10dm ^2, 10
dm ² ), a filter press type bipolar membrane electrodialysis tank having an alkali chamber 13, an acid chamber 14 and a salt chamber 15 was used.

Hydrochloric acid is adjusted to 2N by continuously adding water to the acid chamber, and the hydrochloric acid is added to the salt chamber by adding hydrochloric acid.
A 2N aqueous sodium chloride solution having a magnesium concentration of 5 ppm adjusted to 0.8 and a 2N aqueous sodium hydroxide solution prepared by continuously adding water to the alkali chamber are supplied at a linear velocity of 6 cm / sec. Circulated. Each of the anode chamber and the cathode chamber circulated a 2N sodium sulfate aqueous solution. Electrodialysis was performed at 40 ° C. and a current density of 10 A / dm ² for 10 days. As a result, the cell voltage during energization is
There was no change at 1.7 volts. No precipitate was observed in the cation exchange membrane.

Comparative Example 2 Using the same membrane and battery case as in Example 2, an electrodialysis operation was carried out by continuously adjusting the pH of the salt chamber to 4. As a result, after three days, the cell voltage increased from 1.7 to 3.2 volts, and white precipitates were observed all over the cation exchange membrane.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 B Bipolar membrane C Cation exchange membrane A Anion exchange membrane 1 Anode 2 Cathode 3 Alkaline chamber 4 Acid / salt mixing chamber 11 Anode 12 Cathode 13 Alkaline chamber 14 Acid chamber 15 Salt chamber

Claims (2)

(57) [Claims] 1. A cation exchange membrane and a bipolar membrane are alternately arranged between an anode and a cathode to form an alkali chamber and an acid / salt mixing chamber. In the method for producing an alkali and acid / salt mixed aqueous solution, which respectively takes out an alkali and acid / salt mixed aqueous solution from the chamber and the acid / salt mixed chamber, the pH of the acid / salt mixed aqueous solution in the acid / salt mixed chamber should be less than 1 A process for producing an aqueous solution of an alkali and an acid / salt mixture, characterized in that: 2. A cation exchange membrane, a bipolar membrane, and an anion exchange membrane are sequentially arranged between an anode and a cathode,
An acid chamber and an alkali chamber are formed, and a salt aqueous solution is supplied to the salt chamber to remove an acid and an alkali from the acid chamber and the alkali chamber, respectively, wherein the pH of the salt aqueous solution in the salt chamber is less than 1 A method for producing an acid and an alkali.