JPH06338A - Method for producing acid and alkali - Google Patents

Abstract

(57) [Summary] [Purpose] Acid in the acid chamber is salted even if the seal between the ion exchange membrane and the chamber frame that composes the acid and alkali chambers by bipolar membrane electrodialysis is incomplete. In the chamber, the alkali in the alkaline chamber is prevented from leaking into the salt chamber, thereby preventing damage to the anion exchange membrane. [Structure] 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 an aqueous salt solution is supplied to the salt chamber to supply the acid chamber. In the method for producing an acid and an alkali, respectively, for extracting an acid and an alkali from the alkali chamber, respectively, the linear velocity of the liquid in the salt chamber is faster than the linear velocity of the liquid in the acid chamber and the alkaline chamber, for example, 1.1 times or more. To do.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an acid and an alkali by bipolar membrane electrodialysis of an aqueous salt solution.

[0002]

It is known to produce acids and alkalis by electrodialysis of aqueous salt solutions using bipolar membranes. For example, a three-chamber cell system in which a plurality of cation-exchange membranes, bipolar membranes and anion-exchange membranes are sequentially arranged is disclosed in Japanese Patent Publication No. 32-3962 and Japanese Patent Publication No. 33-69.
No. 63, Japanese Patent Laid-Open No. 63-65912, and the like.

In electrodialysis of an aqueous salt solution using such a bipolar membrane, the alkali chamber is partitioned by a cation exchange membrane and a bipolar membrane, and the acid chamber is partitioned by an anion exchange membrane and a bipolar membrane. . Therefore, the cation exchange membrane is always in contact with the alkaline aqueous solution, and the anion exchange membrane is always in contact with the acid. Therefore, the cation exchange membrane is strong against alkali and the anion exchange membrane is strong against acid. However, the cation exchange membrane is strong against acid,
Anion exchange membranes are extremely sensitive to alkali.

The space between each chamber and each ion-exchange membrane is sealed by a packing, but if the seal is incomplete, the acid in the acid chamber will be in the salt chamber and the alkaline aqueous solution in the alkali chamber will be in the salt. May leak into the room. In this case, the cation exchange membrane partitioning the salt chamber comes into contact with the acid leaking into the salt chamber, and the anion exchange membrane partitioning the salt chamber comes into contact with the alkali leaking into the salt chamber. , Especially leading to damage to the anion exchange membrane.

[0005]

Therefore, according to the present invention, even when the seal between the chamber frame forming each chamber and each ion-exchange membrane is incomplete, the acid in the acid chamber is converted into the salt chamber. It is an object of the present invention to provide a method for preventing an alkaline aqueous solution in an alkaline chamber from leaking to a salt chamber, and particularly for preventing damage to an anion exchange membrane.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have made the linear velocity of a liquid in a salt chamber faster than the linear velocity of a liquid in an acid chamber and an alkaline chamber. According to the above, it was found that the above object can be achieved, and the present invention has been provided.

That is, 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 alkaline chamber, and a salt aqueous solution is placed in the salt chamber. In the method for producing an acid and an alkali, respectively, for removing an acid and an alkali from the acid chamber and the alkali chamber, respectively, wherein the linear velocity of the liquid in the salt chamber is faster than the linear velocity of the liquid in the acid chamber and the alkaline chamber. It is a method for producing an acid and an alkali.

As the electrodialysis tank incorporating the bipolar membrane in the present invention, any known one can be used without any limitation. For example, as shown in FIG. 1, an anode 11 and a cathode 12
And a bipolar membrane (B), an anion exchange membrane (A) and a cation exchange membrane (C) are arranged in this order in order to form three chambers of an alkali chamber 13, an acid chamber 14 and a salt chamber 15. One of the structures can be given. Here, the chamber between the cation exchange membrane (C) and the bipolar membrane (B) is the alkali chamber 13, the chamber between the bipolar membrane (B) and the anion exchange membrane (A) is the acid chamber 14, and the anion exchange membrane. The chamber between (A) and the cation exchange membrane (C) is called the salt chamber 15.

A typical construction of an electrodialysis cell is an anode- (C
-BA-) nC-cathode. Here, the smallest repeating unit composed of a cation exchange membrane, a bipolar membrane, an anion exchange membrane and the like is called a cell, and an assembly of membranes, gaskets and spacers excluding electrodes is called a stack. n is the number of repeated stacks of cells. 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 electrodialysis tank, electrodes used in the electrochemical industry such as water electrolysis and salt electrolysis are used as the anode and cathode without any limitation. For example, nickel, iron, lead, platinum, graphite or the like can be suitably used as the anode material, and nickel, iron, stainless steel, platinum or the like 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. Examples of preferable combinations of these are as follows. Examples thereof 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. Further, preferable combinations of the cathode material and the catholyte are as follows. Mention may be made of nickel, iron or stainless steel-sodium hydroxide, sodium sulphate or saline solution.

The cation exchange membrane used in the present invention is not particularly limited, and known cation exchange membranes can be used.
For example, sulfonic acid group, carboxylic acid group, phosphonic acid group,
It is possible to use a cation exchange membrane having a sulfate ester group or a phosphate ester group, and further a cation exchange membrane in which a plurality of types of these ion exchange groups are mixed. In addition, the cation exchange membrane is a polymerization type,
Condensation type, homogeneous type, heterogeneous type, presence or absence of reinforcing core material, hydrocarbon type, fluorine type, type and type of cation exchange membrane derived from material and manufacturing method Instead, it may be any. Further, an aqueous solution of 2N-saline is electrodialyzed at a current density of 5 A / dm ² , and if it has a current efficiency of 70% or more and substantially functions as a cation exchange membrane, it is generally called an amphoteric ion exchange membrane. Even if it is one, it can be used as the cation exchange membrane of the present invention. Further, 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 stuck together. A known film can be used as such a bipolar film without 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 curing and adhering them (Japanese Patent Publication No. 32-3962), anion exchange membrane and an anion exchange membrane. Method of adhering with an agent (Japanese Patent Publication No. 34-3961), a cation exchange membrane and an anion exchange membrane are coated with a fine powder of an ion exchange resin, or a paste-like mixture of an anion or cation exchange resin and a thermoplastic substance. A method of pressure bonding (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 the paste-like substance (Japanese Patent Publication No. 38- 16633), after adhering a sulfonic acid type polymer electrolyte and allylamines on the surface of an anion exchange membrane, ionizing radiation Irradiation cross-linking method (Japanese Patent Publication No. 51-4113), and a method of depositing a mixture of a base polymer and a dispersion system of an ion exchange resin having an opposite charge on the surface of an ion exchange membrane (Japanese Patent Application Laid-Open No. 53-37190). ), A polyethylene film impregnated with styrene and divinylbenzene and polymerized is sandwiched between sheets and sandwiched in a stainless steel frame, one side is sulfonated, then the sheet is removed and the remaining portion is chlormethylated and then amination-treated. (US Pat. No. 3,562,139) or a method in which the interface between the anion exchange membrane and the cation exchange membrane is treated with an inorganic compound and the both membranes are joined (JP-A-59-472).
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, a quaternary ammonium group, a primary amino group, a secondary amino group, a tertiary amino group, or an anion exchange membrane in which a plurality of these ion exchange groups are mixed can be used. Further, the anion exchange membrane may be of a polymerization type, a condensation type, a homogeneous type or a heterogeneous type, and the presence or absence of a reinforcing core material, a hydrocarbon type, a fluorine type, an anion derived from a material and a manufacturing method. Any ion exchange membrane may be used regardless of the type and model thereof. Further, if a 2N-salt solution is electrodialyzed at a current density of 5 A / dm ² and has a current efficiency of 70% or more and substantially functions as an anion exchange membrane, it is generally called an amphoteric ion exchange membrane. Even so, it can be used as the anion exchange membrane of the present invention. Since an anion exchange membrane tends to easily permeate an acid, it is preferable to use an anion exchange membrane that hardly permeates an acid.

The salt used as the object of electrodialysis in the present invention is not limited to an organic salt or an inorganic salt as long as an acid and an alkali produced by salt decomposition by electrodialysis form an aqueous solution. Can be used without. Examples of the cations forming the salt include sodium, potassium, lithium and ammonium ions. Examples of anions constituting the salt include halogen ions such as fluorine, chlorine, bromine and iodine, sulfate ion, nitrate ion, acetate ion, lactate ion and the like.

The method of electrodialysis in the present invention includes:
For the acid chamber and the alkaline chamber, a method of providing a tank for the liquid to be supplied to each chamber and circulating the respective liquid between the chamber and the tank for the liquid can be preferably adopted.

As a method for extracting the generated acid or alkali, the following method can be preferably adopted.

1. At first, a dilute aqueous acid or alkali solution is charged to generate an acid or alkali, and when a predetermined concentration is reached, a predetermined amount of 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 acid or alkali aqueous solution having a predetermined concentration is charged in advance, and water is continuously added according to the amount of electricity to be applied during energization to overflow the acid or alkaline aqueous solution having a predetermined concentration.

Similarly to the acid and alkali aqueous solutions, the salt aqueous solution is connected to the salt chamber 15 and the salt tank 24 by the salt aqueous solution circulation line 25, and the salt aqueous solution discharged from the salt chamber 15 is passed through the salt tank 24 again. A method of desalting while circulating the water is adopted.

In the present invention, the linear velocity of the above-mentioned salt aqueous solution must be higher than the linear velocity of the acid and alkaline aqueous solutions in the acid chamber and the alkaline chamber. Specifically, the linear velocity of the salt aqueous solution is 1.1 times or more, more preferably 1.2 to 1000 times, usually 2 to 50 times the linear velocity of the acid and alkaline aqueous solutions in the acid chamber and the alkaline chamber. It is preferably within the range. When the linear velocities of the acid and the alkaline aqueous solution in the acid chamber and the alkaline chamber are different from each other, the salt aqueous solution may be supplied at a higher speed than the higher linear velocity.

If the linear velocity of the salt aqueous solution is made faster than the linear velocity of the acid and alkaline aqueous solutions in the acid chamber and the alkaline chamber as described above, the salt aqueous solution leaks to the acid chamber and the alkaline chamber when the sealing is insufficient. However, this does not lead to the damage of the ion exchange membrane.

In the present invention, in order to prevent an increase in voltage of the electrodialysis tank and to prevent leakage of each liquid from the packing surface partitioning the salt chamber, the acid chamber and the alkaline chamber, the line of salt aqueous solution in the salt chamber is prevented. The speed is preferably in the range of 1 to 10 cm / sec. In order to set the linear velocity of the salt aqueous solution in the salt chamber to the above value, it may be determined in consideration of the amount of the salt aqueous solution supplied to the salt chamber and the capacity of the salt chamber. Further, by making the width of the salt chamber as small as 0.5 to 1.0 mm, for example, even when the amount of the salt aqueous solution is small, the above linear velocity can be sufficiently maintained.

The linear velocities of the acid and the alkaline aqueous solution in the acid chamber and the alkali chamber are preferably in the range of 0.01 to 1 cm / sec.

In ordinary ion exchange membrane electrodialysis,
The salt aqueous solution, the acid aqueous solution, or the alkaline aqueous solution is supplied from the lower part of the battery case and discharged from the upper part. However, in bipolar membrane electrodialysis, it is preferable that the acid and alkaline aqueous solutions are supplied from the upper part of the battery case and discharged from the lower part. This is because the concentration of the acid and alkali aqueous solution increases in the battery case, and the higher the concentration of these solutions, the greater the specific gravity. When the liquid is supplied from the lower part to the upper part of the battery case as in the conventional method, the specific gravity becomes larger near the outlet than near the inlet of the battery container, and convection occurs in the battery container. However, when the liquid is supplied from the upper part to the lower part of the battery case, internal convection does not occur in the battery container as it becomes a concentrated aqueous solution of acid and alkali as it goes to the lower part, and furthermore the concentration is the highest in the battery container. The liquid can be taken out.

[0026]

According to the present invention, even when the seal between the chamber frame forming each chamber and each ion-exchange membrane is insufficient, the acid aqueous solution and the alkaline aqueous solution are prevented from leaking into the salt chamber. In particular, it is possible to prevent damage to the anion exchange membrane, and electrodialysis can be stably performed for a long period of time.

[0027]

EXAMPLES In order to more specifically describe the present invention, examples and comparative examples will be given below, but the present invention is not limited to these examples.

Example 1 A bipolar film 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. This polymer solution was subjected to heat polymerization between glass plates at 70 ° C. for 16 hours in a nitrogen atmosphere to obtain a polymer film. Next, the polymer film was added to 96% sulfuric acid to give 6
It was immersed at 0 ° C. for 10 minutes to introduce a sulfonic acid group on the surface of the film material. 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. . This surface has a sulfonated anion exchange membrane and a Tokuyama Soda Co., Ltd. cation exchange membrane (trade name, CM-
During 1), a mixture composed of 5% polyvinyl alcohol and 5% glutaraldehyde in an equal amount was applied, and hot pressing was performed at 50 ° C. for 1 hour for adhesion to obtain a bipolar film.
As the anion exchange membrane and the cation exchange membrane, those manufactured by Tokuyama Soda Co., Ltd. (trade name, AMH, CL-25T) were used.

In the bipolar membrane electrodialysis tank, as shown in FIG. 1, a cation exchange membrane C, a bipolar membrane B, and an anion exchange membrane A are eleven sheets in order between a pair of anion anodes, respectively.
10 sheets, 10 sheets (cation exchange membrane, bipolar membrane, 1 dm ² both effective membrane area of the anion exchange membrane has a total membrane area each 11,10,10dm ²⁾ is arranged, an alkali chamber 13, acid chamber 14 A filter press type bipolar membrane electrodialysis tank in which the salt chamber 15 was formed was used.

In the alkaline chamber, a 4% aqueous solution of sodium hydroxide was supplied from the lower part of the electrodialysis tank at a linear velocity of 0.5 cm / sec, discharged from the upper part and circulated, and ion-exchanged water was continuously added during energization. By doing so, the concentration of sodium hydroxide was increased to 4
Kept at%. In the acid chamber, a 5% sulfuric acid aqueous solution was supplied from the lower part of the electrodialysis tank at a linear velocity of 0.5 cm / sec, discharged from the upper part and circulated, and ion-exchanged water was continuously added during energization to reduce the concentration of sulfuric acid. It was kept at 5%. Each of the anode chamber and the cathode chamber circulated 5 liters of a sodium sulfate aqueous solution (containing 490 g of sodium sulfate). 14.2% sodium sulfate was supplied to the salt chamber at a linear velocity of 3 cm / sec and circulated.

Electrodialysis was carried out at 40 ° C. and a current density of 10 A / dm ² . Electrodes 21 and 22 for detecting stack voltage
Was inserted into the anode chamber and the cathode chamber, and the cell voltage obtained by dividing the measured stack voltage by the number of cell stacks was 2.2 V immediately after the start of electrodialysis, which was unchanged after 96 hours of operation. After that, the electrodialysis tank was disassembled and the anion exchange membrane was observed, but it was not damaged by alkali at all.

Examples 2 and 3 and Comparative Example Electrodialysis was carried out in exactly the same manner as in Example 1 except that the linear velocities of the acid, alkali and salt aqueous solutions were changed to the values shown in Table 1. The results are shown in Table 1.

[0033]

[Table 1]

[Brief description of drawings]

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

[Explanation of symbols]

 A Anion exchange membrane B Bipolar membrane C Cation exchange membrane 11 Anode 12 Cathode 13 Alkaline chamber 14 Acid chamber 15 Salt chamber 21,22 Stack voltage detection electrode 23 Salt aqueous solution supply line 24 Salt tank 25 Salt aqueous solution circulation line 26 Voltage Total

Claims (1)

[Claims] 1. 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,
In the method of producing an acid and an alkali, which form an acid chamber and an alkali chamber, and supply an aqueous salt solution to the salt chamber to take out the acid and the alkali from the acid chamber and the alkali chamber, respectively, the linear velocity of the liquid in the salt chamber is set to the acid chamber and the alkali chamber. A method for producing an acid and an alkali, which comprises increasing the linear velocity of a liquid in a chamber.