JPS5814510B2 - Aeon Koukan Makuden Kaihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for electrolyzing an aqueous alkali halide solution to efficiently obtain a highly concentrated caustic alkali.

Halogens and caustic alkalis are important chemicals required in all industrial fields, and in particular chlorine and caustic soda are obtained by electrolysis of common salt and are used in large quantities.

However, in Japan, which is particularly lacking in natural resources, electrolysis using salt from the four seas as a raw material has been attempted for a long time, but it has not yet been put to industrial use.

The present invention is an electrolysis method characterized by obtaining a high concentration of caustic alkali using a simpler battery container than a low concentration aqueous halide aqueous solution, and is particularly suitable for the production of industrial caustic soda by electrolysis of seawater or low concentration brine. It makes it seem possible.

As a result of research for this purpose, the present inventors found that
According to ion-exchange membrane electrolysis using a low-concentration alkaline halide solution, all the water necessary to produce the caustic soda solution is transferred from the alkaline halide solution to the cathode together with alkali metal ions, and in this case, the anode chamber and the cathode chamber are separated. The present inventors have discovered that by providing an intermediate chamber between them, a highly concentrated caustic alkaline solution with a low halogen ion content can be obtained in the cathode chamber with high current efficiency, resulting in the present invention.

The present invention uses two cation exchange membranes to provide an anode chamber, an intermediate chamber,
Using a separate container in the outer electrode chamber, an aqueous halide aqueous solution with a concentration of 20 or less is supplied to the anode chamber, and aqueous caustic alkaline solution is supplied to the intermediate chamber and cathode chamber without supplying any water from the outside. This is an electrolytic method that simultaneously obtains high and low concentration caustic alkali, which is characterized by being supplied from the anode chamber.

The first feature of the invention is the use of a low concentration of alkali halide brine.

The second feature is that although it is a three-chamber method, there is no need to supply water to the intermediate chamber and the cathode chamber, making the structure of the battery cell extremely simple.

The third feature is that the highly concentrated caustic alkali obtained in the present invention contains only a very small amount of halogenated alkali and is of extremely good quality.

The details of the present invention will be explained below by taking the electrolysis of common salt as an example, but it goes without saying that the same holds true for other alkali halides.

In general salt electrolysis, Na is supplied to the anode chamber.
A saturated Cl aqueous solution with a concentration of 26 parts or more is used, but in the present invention, a low concentration aqueous solution of 20 parts or less is used.The amount of water passing through the ion exchange membrane (hereinafter referred to as A membrane) on the anode side is determined by the current It depends on the efficiency (ie the water moving with Na+ and OH-) but also on the concentration of NaOH in the intermediate chamber and NaCl in the anode chamber.

In particular, the latter NaCl concentration can be adjusted, and if the NaCl concentration in the anode chamber is effectively sufficiently lower than the concentration in the intermediate chamber, a sufficient amount of water can pass through the NaOH produced.

The ratio between the part that depends on the current efficiency of the moving water and the part that depends on the salt concentration in the anode chamber and the intermediate chamber has not yet been accurately measured, and the two probably have a confounding relationship with each other and cannot be clearly defined. It is thought that they cannot be separated, but in any case, as long as there are virtually no pinholes in the A membrane and water does not flow directly (not through electrophoresis) from the anode chamber, the ions in the saline solution are close to saturation. It is difficult to transfer sufficient water to the intermediate chamber by exchange electrolysis, and the NaCl concentration is
Must be less than 0 weight.

For example, when producing 50 parts by weight of caustic soda at a current efficiency of 80%, 90%, and 95 parts, the theoretically required amount of water is about 1.9 g/A-h, 2.09/A-h, and 2.0 g/A-h, respectively. 1g
/A-h, and if 40 parts by weight of caustic soda were to be produced with similar current efficiency, the amounts of water required would be approximately 2.5 F/A-h, 2.79/A-h, and 2, respectively. .8F/
It is A-h.

When the ion exchange membrane NAFION No manufactured by E.I. DuPont, which is currently supplied for salt electrolysis, is used between the anode chamber and the intermediate chamber, and saturated saline is supplied to the anode chamber, the water permeation rate is 2.0 g/ A-h @ later, and speaking only from the performance of the A membrane, it should be theoretically possible to produce caustic soda with a concentration of 50% by weight or higher, but the caustic soda that enters the intermediate chamber is further concentrated in the cathode chamber. As a result, the alkali concentration becomes too high and operation becomes impossible.

Furthermore, as will be described later, the ion exchange membrane on the end pole side (hereinafter referred to as B membrane) must always have a lower water permeability than A membrane.

Even if a membrane with a water permeability of 2.0 g/A-h or less is used as a B membrane, if the difference in water permeability between the two membranes is small, the desirable performance of both membranes will deteriorate due to clogging or deterioration of the membrane during electrolysis operation. If even the slightest change occurs, stable operations will no longer be possible.

Therefore, it is necessary to lower the NaCl concentration to increase the amount of water permeation through the A membrane, so that even if the performance of the membrane changes slightly and the caustic soda concentration in the intermediate chamber and cathode chamber changes considerably, the operation will not become difficult. .

A NaCl concentration of 20% by weight or less was determined as a condition for stable operation.

The lower limit of the NaCl concentration may be any concentration that does not significantly increase the electrical resistance of the anolyte, and is usually preferably 2 weight percent or more.

If the amount of water permeable through the A membrane is too large, the caustic soda may become too thin.

However, for example, when using 20% by weight of caustic soda, the current efficiency is 95%.
The amount of water required is approximately 6.3 g/A-h, but when the salt concentration in the anode chamber is 2 weight percent or more, the amount of water required is approximately 6.3 g/A-h.
Under the conditions of m2, a practical pinhole-free ion exchange membrane would not have such a large amount of water permeation.

The properties required for membrane A are good ion exchange ability, appropriate water permeability, and excellent chlorine resistance and oxidation resistance. Most preferably, an ion exchange membrane made of fluororesin is used. be.

However, if the chemical resistance of the A membrane is poor, a furnace diaphragm with excellent chemical resistance is installed between the anode and the A membrane to divide the anode chamber into two and prevent chlorine gas from coming into direct contact with the A membrane. Therefore, the A membrane does not necessarily need to be a fluororesin ion exchange membrane.

In addition, the A membrane has low permeation of OH, at least NaOH
Since it is desired to have a current effect of a factor of 80 or more, it is desirable to use a material with as large a Na ion exchange capacity as possible.

The concentration of the combined NaOH aqueous solution coming out of the intermediate chamber and the cathode chamber is determined by the amount of water passing through the A membrane and the current efficiency.

However, how the NaOH is distributed between the cathode chamber and the intermediate chamber depends on the properties of the ion exchange membrane (B membrane) on the cathode side.

The amount of water permeable through the B membrane must necessarily be smaller than the amount of water permeable through the A membrane.

Otherwise, the NaOH concentration in the intermediate chamber will be higher than that in the cathode chamber, the current efficiency of the A membrane will be poor, and the purpose of obtaining high-concentration, high-purity caustic alkali will not be met. As it decreases, gas accumulates inside, making it impossible to continue operation.

Examples are shown below, and the numbers in the examples refer to weights.

Example 1 The electrolytic cell used in the experiment is as shown in the attached figure.The electrolytic cell 1 consists of an anode chamber 2, an intermediate chamber 3, and a cathode chamber 4, and the outer wall blocks of each are connected with bolts as shown in the figure. The top and surrounding bolts are not visible).

At this time, the anode 5 and the ion exchange membrane A are interposed between the anode chamber and the intermediate chamber, and the cathode 6 and the ion exchange membrane B are interposed between the cathode chamber and the intermediate chamber, thereby separating the respective chambers.

The anode chamber 2 is provided with a brine population 7 and an outlet 8,
Chlorine is discharged from the outlet 8 along with the return brine.

The intermediate chamber 3 is provided with a dilute caustic soda outlet 9, and the cathode chamber 4 is provided with a concentrated caustic soda and hydrogen gas outlet.

The anode 5 was made of titanium coated with ruthenium oxide, and the cathode 6 was made of iron wire mesh.

As ion exchange membrane A, NA manufactured by E.I. DuPont
FION315 membrane (NAFION EW-1100 and N
AFION EW-1500 and an ion exchange membrane laminated with tetrafluoroethylene resin mesh) were treated with chlorosulfonic acid, a copolymer of methyl acrylate, divinylbenzene, and stellane, to create a sulfonated membrane as ion exchange membrane B. NaCl was electrolyzed using the following.

A 6-layer aqueous solution of NaCl is supplied to the anode chamber, and the current density is 2.
Electrolysis was performed under the condition of 0 A/dm2.

At the start of the experiment, 1O% was added to the intermediate chamber and cathode chamber, respectively.
Fill each chamber with 30 parts of NaOH solution.
The electrolytic conditions were measured when the concentration became steady.

The results are shown in Table 1. Example 2 Using the same apparatus as in Example 1, NAFION 390 membrane (NAFION NEW ~ 15
00, EW-iioo and tetrafluoroethylene resin mesh), NAFION425 membrane (NAFION NEW
-1200 and an ion exchange membrane laminated with a tetrafluoroethylene resin mesh), electrolysis of NaCl was performed.

An aqueous NaC16 solution was supplied to the anode chamber, nothing was supplied to the intermediate chamber and the cathode chamber, and electrolysis was carried out at a current density of 20 people/am2.

The results are shown in Table 2. Using the same electrolytic cell as in Example 1,
NAFION315 as the membrane A between the anode chamber and the intermediate chamber
As a membrane B between the intermediate chamber and the cathode chamber, Teflon paper was impregnated with 50% by weight of bunal methacrylate and 50% by weight of divinylbenzene, and a molded product was prepared by polymerizing in nitrogen using penzoyl peroxide as a catalyst, in concentrated sulfuric acid. Using the treated membrane, electrolysis was performed using an 18% NaCl aqueous solution as the anolyte.

The results are shown in Figure 3.

Control Example Using the same membrane and equipment used in Example 3, NaCl
When electrolysis was carried out at a concentration of 26%, the liquid in the intermediate chamber gradually decreased, and finally the voltage suddenly rose, and the temperature of the liquid in the cathode chamber rose sharply, making it impossible to conduct electricity.

Therefore, in order to measure the amount of water permeation through the ion exchange membrane, a 26% NaCl solution was also supplied to the anode chamber, and water was also supplied to the intermediate chamber (in this case, the electrolytic cell was equipped with a water inlet also in the intermediate chamber). An electrolytic experiment was conducted in the same manner as in Example 3), and the water permeability of membranes A and B was measured, and the water permeation of membrane A was 2.1.
89/A-h, the water permeability of membrane B is 2.299/A-h, or the cell voltage is 4.2■, the NaOH concentration in the current efficiency chamber is 4.0% and 41.8%, respectively, and the intermediate Although it is thought that the amount of water permeable is slightly different from the amount of water permeable when no water passes through the chamber, the result that the amount of water permeable through membrane B is higher than the amount of water through membrane A measured here is due to the fact that the amount of water permeable through membrane B is greater than the amount through which water is passed through the intermediate chamber. This is consistent with the above experimental results in which the liquid in the intermediate chamber decreased when there was no

[Brief explanation of the drawing]

The accompanying drawing is a schematic diagram of a typical battery case used in the present invention. 1... Electrolytic cell, 2... Anode chamber, 3... Intermediate chamber, 4... Cathode chamber, 5... Anode, 6... Cathode, 7, 8... Brine inlet and outlet, 9, 10... Intermediate Caustic alkali outlet from chamber and cathode chamber, A, B...Cation exchange membrane.

Claims (1)

[Claims] 1 Using a container containing an aqueous halide aqueous solution divided into an anode chamber, an intermediate chamber, and a cathode chamber by two cation exchange membranes, a low concentration of caustic alkali is obtained from the intermediate chamber and a high concentration of caustic alkali from the cathode chamber. In electrolysis, an alkali halide aqueous solution with a concentration of 20 parts or less is supplied to the anode chamber, no water is supplied from the outside to the intermediate chamber and the cathode chamber, and all the water necessary for the caustic alkaline aqueous solution to be generated is supplied from the anode chamber. An ion exchange membrane electrolysis method characterized by osmotic transfer through an ion exchange membrane.