JPH0663365A - Method and device for electrodialysis - Google Patents

Abstract

PURPOSE:To efficiently produce free acid from org. acid salt by providing a substitution chamber surrounded by a cation-exchange membrane and a cation- exchange membrane between an anode compartment and a cathode compartment and/or a desalting chamber enclosed by an anion-exchange membrane and a cation-exchange membrane to constitute an electrodialytic cell. CONSTITUTION:At least one substitution chamber 5 surrounded by a cation- exchange membrane 1 and a cation-exchange membrane 2 is provided between an anode compartment 7 and a cathode compartment 8, and the concentration chamber 6 and/or desalting chamber 4 enclosed by an anion-exchange membrane 3 and a cation-exchange membrane and adjacent to the chamber 5 are furnished to constitute an electrodialysis cell. Consequently, a free acid (e.g. lactic acid) is efficiently produced from org. salts of a weak or strong acid (e.g. sodium lactate), and further a cation constituting a salt (e.g. sodium benzenesulfonate) is replaced with an optional other cationic acid (e.g. benzenesulfonic acid).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electrodialysis method. Specifically, it relates to cation exchange of organic salts and inorganic salts using electrodialysis. More specifically, it relates to a method for producing a free acid by substituting hydrogen ion for a cation of an organic salt or an inorganic salt, or a method for substituting a cation constituting a salt with another cation.

[0002]

2. Description of the Related Art Conventionally, as a method for exchanging cations by using electrodialysis, for example, Japanese Patent Publication No. 30-5613 and Japanese Patent Publication No. 62-56953 have a plurality of methods between an anode chamber and a cathode chamber. Cation exchange membranes are arranged, and the chambers partitioned by the membranes are alternately set as a strong acid chamber and a salt chamber, and a salt of a high-molecular acid or an organic acid is placed in the salt chamber, and an aqueous solution of mineral acid is placed in the strong acid chamber. A method for obtaining a free polymeric acid or an organic acid by supplying and supplying a direct current is proposed. In these methods, the cations in the salt chamber are discharged from the cation exchange membrane on the cathode side of the salt chamber and the hydrogen ions in the strong acid chamber are taken in from the cation exchange membrane on the anode side of the salt chamber by applying a direct current. Is a method of converting the organic acid salt in the salt chamber into a free acid.
Each of these is a method that applies the property that the cation exchange membrane is more permeable to hydrogen ions than to metal ions.

[0003]

However, in these known methods, since the metal ions once discharged from the salt chamber are contained in the strong acid chamber, the metal ion concentration in the strong acid chamber increases as the operation continues. . Therefore, unless the mineral acid solution is appropriately renewed, there is a problem that the metal ions in the mineral acid solution permeate into the salt chamber again and the purity of the generated organic acid decreases.

Although these methods are effective for producing weakly acidic high molecular weight acids and organic acids, they are not used when the organic acids are strongly acidic. This is because in the case of a strongly acidic organic acid, the hydrogen ion concentration increases as free acid is generated in the salt chamber, so the ratio of hydrogen ions to the total cations discharged from the salt chamber to the cathode side becomes high and the efficiency increases. Is significantly worse. Therefore, in order to obtain a high-purity free acid, it is necessary to repeat the renewal of the mineral acid for the purpose of supplying only hydrogen ions to the salt chamber, which is not economical.

The present invention solves the problems in the above method and provides a method for efficiently producing a free acid from an organic acid salt regardless of weak acidity or strong acidity.
Further, the present invention not only provides a method for producing a free acid but also a method for substituting a cation constituting a salt with any other cationic acid.

[0006]

Means for Solving the Problems As a result of intensive studies on a method of exchanging cations by electrodialysis, the present inventor has an anode chamber and a cathode chamber, and a cation exchange membrane and a cation exchange membrane sandwich it. An electrodialysis apparatus comprising at least one replacement chamber and an electrodialysis tank having a concentration chamber and / or a desalination chamber sandwiched between at least one side of the anion exchange membrane and the cation exchange membrane. The inventors have found that the above objects can be achieved, and have completed the present invention.

That is, a free acid can be obtained from the salt in the intermediate chamber by supplying a salt aqueous solution to the intermediate chamber of the apparatus of the present invention and a strong acid aqueous solution to the desalting chamber and applying a direct current. . Further, an aqueous solution of a salt of anion A and a cation B is supplied to the intermediate chamber and an aqueous solution of a salt of anion C and a cation D is supplied to the desalting chamber, and a DC current is applied to supply the salt in the intermediate chamber. It is possible to substitute the cation B constituting the cation with the cation D to form a salt composed of the anion A and the cation D. Next, the method of the present invention will be described with reference to the drawings. However, the drawings show only one example of an apparatus used by the method of the present invention, and the present invention is not limited thereby.

First, a method for producing a free acid from a salt will be described. The electrodialysis tank is separated into a desalting chamber 4, a substitution chamber 5 and a concentrating chamber 6 by the cation exchange membranes 1 and 2 and the anion exchange membrane 3 shown in FIG. The deionization chamber 4 has a tank 9
The strong acid aqueous solution is circulated by a pump. A metal salt of an organic acid, for example, is circulated and supplied from the tank 10 to the substitution chamber 5. Waste liquid is circulated and supplied from the tank 11 to the concentration chamber 6. This waste liquid may be simple water or an aqueous solution of salt or strong acid at the start of the first operation, but it does not need to be updated for each batch when repeating the batch operation, and it can be used continuously in the state of the previous batch. May be. Aqueous solution of strong acid is circulated and supplied from the tank 12 to the anode chamber 7 and the cathode chamber 8.

When a direct current is applied, cations are electrophoresed toward the cathode and anions are electrophoresed toward the anode, but the cation exchange membrane allows the cations to pass but prevents the permeation of the anions. In addition, the anion exchange membrane has a function of blocking the permeation of cations while permeating anions. Therefore, the strong acid in the desalting chamber 4 is desalted because hydrogen ions move through the cation exchange membrane 2 to the substitution chamber 5 and anions pass through the anion exchange membrane 3 to the concentration chamber 6. The concentration of the liquid decreases. Therefore, in order to maintain the concentration of the strong acid in the tank 9, a strong acid having a high concentration is supplied from the tank 13.

In the substitution chamber 5, metal ions of the organic acid salt are removed from the cation exchange membrane 1 to the concentration chamber 6, and at the same time hydrogen ions are supplied from the cation exchange membrane 2, so that the desired free organic acid is gradually added. Will be obtained. A high-concentration waste liquid is generated in the concentrating chamber 6 due to the metal ions from the substitution chamber 5 and the strong acid anions in the desalting chamber 4.

As described above, the feature of the method of the present invention is that the deionization chamber 4 does not increase the concentration of cations other than hydrogen ions even after long-term operation. 5 can be supplied to the substitution chamber 5, and thus a high-purity free organic acid can be produced in the substitution chamber 5. Further, the method of the present invention is characterized in that a free acid can be economically produced from a salt of a strongly acidic organic acid without liquid renewal. When a strongly acidic organic acid is produced, the hydrogen ion concentration in the substitution chamber 5 also rises as the free acid is produced in the substitution chamber 5. Therefore, hydrogen ions gradually increase as cations that permeate the cation exchange membrane 1 and move to the concentrating chamber 6. Therefore, if an attempt is made to increase the conversion rate to free acid, the desalting chamber 4 will be replaced by the substitution chamber 5
It would require several times the equivalents of strong acid to the equivalents of the organic salt fed to, but surprisingly, much less equivalents of strong acids would actually be required. The reason for this is presumed as follows. As described above, generally, anions pass through the anion-exchange membrane, but they have a function of blocking the permeation of cations, but exceptionally, the permeation of hydrogen ions cannot be sufficiently blocked. Therefore, the hydrogen ions once moved to the concentrating chamber 6 permeate the anion exchange membrane 3 and move to the desalting chamber 4, and are utilized again to convert the organic salt in the substitution chamber 5 into an organic acid. That is, it can be said that hydrogen ions are recycled and used inside the electrodialysis tank.

Although the production of the free acid has been described above, the use of the apparatus of the present invention enables the cation exchange of salts, which has been difficult by the electrodialysis method. That is, the substitution chamber is supplied with an aqueous solution of a salt of an anion A and a cation B, and the desalting chamber is supplied with an aqueous solution of a salt of an anion C and a cation D. It is possible to form a salt composed of an anion A and a cation D. As an example thereof, it can be used when obtaining a potassium salt of an organic acid from a sodium salt of an organic acid. In this case, the aqueous solution of the sodium salt of an organic acid is supplied to the substitution chamber 5, and the aqueous solution of the inorganic salt having potassium ions such as potassium chloride is supplied to the desalination chamber 4, and a direct current is applied to the substitution chamber 5 for the purpose. A potassium salt of an organic acid can be obtained. Generally, there is no great difference in the permeation characteristics of the cation exchange membrane between sodium ion and potassium ion, and therefore potassium ions also permeate from the substitution chamber 5 to the concentration chamber 6 as the conversion rate increases. As long as only potassium ions are constantly supplied to the desalting chamber 4, the replacement chamber 5 will eventually be provided.
It is possible to convert almost all of the organic acid salts of to the potassium salt.

The ion exchange membrane used in the present invention is not particularly limited, and any one used in the salt industry or desalination can be used. The strong acid used for producing the free acid is preferably an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid, but is not particularly limited. In the exchange of salt cations, the type of cation to be exchanged is not limited in any way, and it can be used for both inorganic ions and organic ions. Similarly, the anion component of the salt is not limited.

In the description of the present invention, the method of adding the supply acid from the supply acid tank 13 to the strong acid tank 9 to be supplied to the desalting chamber has been described. However, a constant amount of the strong acid is supplied to the tank 9 in advance. It doesn't matter how you do it. But,
The former is preferable for operating the device under stable conditions.

[0015]

The following examples will explain how the present invention can be implemented.

[0016]

Example 1 A test for obtaining lactic acid from sodium lactate by the method of the present invention was conducted. Ashiplex (registered trademark) K-101 manufactured by Asahi Kasei Corporation as a cation exchange membrane,
Adiaplex (registered trademark) A-201 manufactured by Asahi Kasei Kogyo Co., Ltd. is used as an anion exchange membrane, and the configuration shown in FIG. 1 is used, and the number of desalting chambers, substitution chambers, and concentration chambers is 10 each. Was produced. The current-carrying area of this device is 55 cm ² , and the thickness of the desalting chamber, the replacing chamber and the concentrating chamber are each 0.7.
It is 5 mm.

300 ml of 0.2N sulfuric acid as an electrode solution
As waste liquid, 300 ml of 0.1N sulfuric acid, 300 ml of 0.2N sulfuric acid as desalting liquid, and 5 ml as supplied acid liquid.
Sulfuric acid of N was prepared, and the supply acid solution was automatically supplied to the desalting solution tank by a metering pump so that the conductivity of the desalting solution could be detected and the conductivity could be maintained at 50 mS / cm. Using 500 ml of 1N sodium lactate aqueous solution as the sample solution to be circulated and supplied to the substitution chamber, the electrode solution, the desalting solution, the waste solution, and the sample solution (stock solution) are circulated in the electrodialysis tank respectively, and a direct current of 2 A is applied for 50 minutes. did. As a result, the volume of sample liquid is 4
In 96 ml, the concentration of sodium ion was 0.002N. That is, about 99.8% of sodium lactate could be converted to lactic acid. The consumption of the supplied acid solution is 106m.
It was l. This amount corresponds to 1.06 times the equivalent of sodium lactate in the first sample solution.

[0018]

Example 2 A test for obtaining benzenesulfonic acid from sodium benzenesulfonate, which is a salt of a strongly acidic organic acid, was carried out by the method of the present invention. Equipment, electrode fluid, desalination fluid, waste fluid,
The acid solution supplied was under the same conditions as in Example 1. Sample solution (stock solution)
As a 1N aqueous solution of sodium benzenesulfonate 50
A direct current of 2 A was applied for 150 minutes using 0 ml. As a result, the volume of the sample liquid was 502 ml and the concentration of sodium ions was 0.19N. That is, about 81% of sodium benzenesulfonate could be converted to benzenesulfonic acid. The consumption of the supplied acid solution is 214
ml, which corresponds to 2.14 times equivalent of sodium benzenesulfonate in the original sample solution.

[0019]

Example 3 A test for obtaining potassium lactate by replacing sodium in sodium lactate with potassium by the method of the present invention was conducted. The same apparatus as in Example 1 was used, and 300 ml of 0.5 N potassium sulfate aqueous solution was used as the electrode solution, 300 ml of 0.1 N potassium sulfate aqueous solution was used as the waste liquid, and 300 ml of 0.5 N potassium sulfate aqueous solution was used as the desalting liquid. I was there. Also, prepare a 4N potassium sulfate aqueous solution as a solution to be supplied to the desalting solution tank, and automatically detect the conductivity of the desalting solution by a metering pump so that the conductivity can be maintained at 50 mS / cm. It was possible to supply to the salt solution tank. As a sample solution to be supplied to the substitution chamber, 500 ml of a 1N sodium lactate aqueous solution was used, and a direct current was applied at a current of 2 A for 150 minutes. As a result, sodium lactate 94.4
% Could be converted to potassium lactate. The amount of 4N potassium sulfate aqueous solution consumed was 420 ml.

[0020]

INDUSTRIAL APPLICABILITY The electrodialysis method of the present invention is an excellent method for producing a high-purity free acid from a salt or for substituting a cation constituting the salt.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an electrodialysis method of the present invention.

[Explanation of symbols]

 1, cation exchange membrane 2, cation exchange membrane 3, anion exchange membrane 4, deionization chamber 5, substitution chamber 6, concentration chamber 7, anode chamber 8, cathode chamber 9, desalination tank 10, stock solution (sample Liquid tank 11, waste liquid tank 12, electrode liquid tank 13, supply acid tank

Claims (3)

[Claims] 1. A cation exchange having an anode chamber and a cathode chamber, at least one cation exchange membrane and at least one substitution chamber sandwiched between the cation exchange membranes, and at least one side of the anion exchange membrane and the cation exchange membrane. An electrodialysis device comprising an electrodialysis tank having a concentration chamber and / or a desalting chamber sandwiched between membranes. 2. The anion A in the substitution chamber according to claim 1.
An electrodialysis method characterized in that an aqueous solution of a salt consisting of cation B and an aqueous solution of acid C is supplied to the desalting chamber and a DC current is applied to generate an acid of A in the intermediate chamber. 3. The anion A in the substitution chamber according to claim 1.
An aqueous solution of a salt of cation B and a cation B, and an aqueous solution of a salt of anion C and a cation D are supplied to the desalting chamber, and a direct current is applied to the anion A and cation D to the displacement chamber. An electrodialysis method characterized in that a salt consisting of is produced.