JPS6046188B2 - Diaphragm method Alkali chloride electrolysis method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diaphragm alkaline chloride electrolysis method.

Diaphragm method alkali chloride electrolysis uses a filter diaphragm such as an asbestos membrane or an ion exchange membrane as a diaphragm to electrolyze an aqueous alkali chloride solution to obtain caustic alkali and chlorine.

Specifically, an electrolytic cell is used in which an anode and a cathode are separated by a diaphragm to form an anode chamber and a cathode chamber, and purified saturated or nearly saturated salt water (Ca content, Mg content, etc. The alkali chloride is electrolyzed by electrolysis to obtain chlorine from the anode chamber and caustic soda from the cathode chamber. According to the findings of the present inventor, in such an electrolysis method, as the alkali chloride concentration of the solution in the anode chamber (hereinafter referred to as anolyte) increases, the current efficiency increases, the electrolysis voltage decreases, and high purity chlorine gas increases. I found out that I can get it.

However, even if a saturated or nearly saturated aqueous alkali chloride solution is supplied to the anode chamber, the alkali chloride concentration in the anode chamber decreases because the alkali chloride is decomposed and consumed by electrolysis.

Part 9: The present inventor has achieved the goal of reducing the chloride concentration in the anode chamber by shortening the residence time of the anolyte and, specifically, by increasing the volume of the saturated or nearly saturated aqueous alkali chloride solution supplied to the anode chamber per unit time. An attempt was made to suppress the decomposition rate of alkali and increase the alkali chloride concentration in the anolyte.

However, this method requires the use of alkali chloride aqueous solution supply equipment (pumps, piping, etc.) as the decomposition rate of alkali chloride decreases.
It is difficult to reduce the decomposition rate excessively, as this increases the burden of refining the supplied aqueous alkali chloride solution and, above all, increases the burden of refining the supplied aqueous alkali chloride solution. Ivy. Therefore, the present inventors have conducted extensive research with the aim of successfully increasing the alkali chloride concentration of the anolyte without causing the above-mentioned drawbacks, and have therefore provided the present invention. The present invention relates to a method for electrolyzing an aqueous alkali chloride solution using an electrolytic cell formed by partitioning an anode and a cathode with a diaphragm and forming an anode chamber and a cathode chamber. The diaphragm method is an alkali chloride electrolysis method that supplies an aqueous alkali chloride solution close to that of the diaphragm method.

According to the present invention, since solid alkali chloride is contained in the supplied saturated or nearly saturated aqueous alkali chloride solution, when the dissolved alkali chloride is consumed by electrolysis in the anode chamber and the alkali chloride concentration decreases, The coexisting solid alkali chloride is dissolved in the liquid, and the alkali chloride concentration of the anolyte is maintained at a high level.

In the present invention, solid alkali chloride refers to solid alkali metal chloride, and specific examples include solid NaCl. ．．
It is KCl.

This solid alkali chloride is preferably pure alkali chloride that does not contain impurities such as Ca and Mg, but is not limited to this, and may contain trace amounts of impurities that do not have a negative effect on the diaphragm. I can't replace it. It is preferable that the solid alkali chloride dissolves quickly in the liquid as the concentration of the coexisting aqueous alkali chloride solution decreases.For this purpose, the shape of the solid alkali chloride should be granular, powdery, or flaky. It is preferable that the diameter is 10 to 300μ. Although it is possible to use particles smaller than 10p,
This is not very preferable because it takes time and effort to grind. Within the above range, it is more preferably 50 to 150μ.

Further, from the viewpoint of solubility, it is preferable to use a hydrated form of the solid alkali chloride. The aqueous alkali chloride solution is an aqueous solution of alkali metal chloride, specifically N
They are aCl aqueous solution and KCl aqueous solution. A saturated or nearly saturated aqueous aqueous solution of alkali chloride is generally prepared by dissolving the raw material salt in water to reach a saturated or nearly saturated alkali chloride solution [7] After that, it is purified to remove impurities such as Ca and Mg in the solution. You can get it.

Others are refined but have a low alkali chloride concentration.
It can also be obtained by adding the solid alkali chloride mentioned above to an aqueous alkali chloride solution. It should be noted that an aqueous alkali chloride solution that is nearly saturated is one that is so saturated with alkali chloride that even if solid alkali chloride is allowed to coexist therein, the alkali chloride can maintain its solid state. In the present invention, a saturated or nearly saturated aqueous aqueous alkali chloride solution containing the solid alkali chloride described above is supplied to the anode chamber.

In this case, solid alkali chloride coexists at least until it enters the anode chamber.

In the anode chamber, alkali chloride dissolved in the anolyte is consumed by electrolysis, so theoretically, solid alkali chloride is dissolved in an amount corresponding to the amount of consumed alkali chloride. Therefore, if the weight of solid alkali chloride supplied per unit time is approximately equal to or less than the amount of alkali chloride decomposed and consumed by electrolysis per unit time in the anode chamber, When dissolution occurs quickly, there is almost no solid alkali chloride present in the anolyte.

However, there are cases in which solid alkali chloride does not dissolve quickly, and in such cases, solid alkali chloride is present in the anolyte.

If a large amount of solid alkali chloride is present in the anolyte, the diaphragm, especially a filter diaphragm such as an asbestos membrane, will become clogged. It is preferable to specifically dissolve it in the anolyte as quickly as possible.

Various methods can be used to supply the solid alkali chloride.

For ease of understanding, alkali chloride will be explained as NaCl.

For example, solid salt may be added to the electrolyte solution supplied to the anode chamber, that is, saturated or nearly saturated salt water obtained by dissolving raw material salt in water and purifying it, and then supplying this to the anode chamber. salt can be supplied directly to

Another method is to supply saturated or nearly saturated salt water to the anode chamber, draw out a portion of the anolyte outside the anode chamber, and add solid salt to it to make it saturated or saturated, including solid alkali chloride. It is also possible to use nearly salt water and recirculate it to the anode chamber.

In the latter method, which involves recycling the anolyte, the amount of common salt added must be at or above the amount necessary to bring the extracted anolyte to saturation or near saturation. Especially in the latter case, during the process of recirculating the anolyte, the solid salt begins to dissolve, and when it enters the anode chamber, the particle size is also much smaller, compared to the former method. This is preferable because it becomes easily soluble.

In these methods, solid salt may be added continuously or in batches.

As for the method of adding solid salt, it goes without saying that it can be added in solid form to purified salt water or the anolyte, but it can also be added in the form of a slurry. The method of the present invention can be applied to an alkali chloride electrolysis method using a diaphragm such as an asbestos membrane or an ion exchange membrane, but is particularly applicable to an alkali chloride electrolysis method using a filtration diaphragm such as an asbestos membrane. is preferred. For example, in asbestos diaphragm electrolysis, the electrolytic solution obtained from the cathode chamber contains caustic alkali and alkali chloride. A portion of the alkali chloride is precipitated and separated. Then, if necessary, the aqueous caustic alkali solution from which most of the alkali chloride has been separated is cooled to precipitate the remaining alkali chloride as hydrate crystals. Separated. These precipitated alkali chlorides hardly contain Ca, Mg, etc., which have a negative effect on the diaphragm.

Therefore, these precipitated alkali chlorides can be used as the solid alkali chloride of the present invention. When the present invention is applied to the filtration diaphragm electrolysis method in this way, the alkali chloride in the electrolyzed solution obtained from the cathode chamber can be effectively utilized. Next, an example of implementing the present invention will be described.

Example 1 An anode (expanded metal made of titanium plated with ruthenium oxide) and a cathode (expanded metal made of iron) are separated by an asbestos film, and the anode chamber of an electrolytic cell having an anode chamber and a cathode chamber is purified to a NaCl concentration of 325 y/e. Salt water was supplied at a rate of 1000 e/hr, and solid NaCl having an average particle size of 75 μm was added in batches (3k9 per powder) to the supplied salt water to perform electrolysis.

Chlorine gas (Cl2:98.4%, 02:1.
A caustic soda aqueous solution was taken out from the cathode chamber at a rate of 790'/Hr. The resulting solution was boiled down in an evaporation can to precipitate NaCl, which was separated.

This solid NaCl was used as the solid NaCl described above. ), the NaCl concentration of the solution in the anode chamber is 290y.
/e1 temperature was 94°C, sliding voltage was 3.48V1, and current efficiency was 98%.

Comparative Example 1 Using the same electrolytic cell as in Example 1, the anode chamber had a NaCl concentration of 3.
Electrolysis was carried out by supplying 25 y/e of purified salt water at 1000 e/hr.

(Do not add solid NaCl) Chlorine gas from the anode chamber
It was obtained at a ratio of 9.5N7T1/Hr and its composition was Cl.
They were 97.8% and 022.2%.

), the NaCl concentration of the solution in the anode chamber is 275 g/'
, temperature is 94℃, sliding voltage is 3.50V1, current efficiency is 95
．． It was 5%. Example 2 Purified salt water of 325 J/e was supplied to the anode chamber of the same electrolytic cell as in Example 1 at 1000 e/hr, and a part of the liquid was transferred from the anode chamber to the tank outside the tank for 1000 e/hr.
Solid Na is extracted at a rate of 0e/Hr, and
After adding Cl at a rate of 30 kg/Hr, it was circulated to the anode chamber.

The composition of the chlorine gas was Cl298.5% and Cl21.5%.

), the NaCl concentration of the solution in the anode chamber is 2901/e.
1 temperature is 94℃, sliding voltage is 3.48V1 current efficiency is 98
．． It was 0%.

Claims (1)

[Scope of Claims] 1. A method for electrolyzing an aqueous alkali chloride solution using an electrolytic cell in which an anode and a cathode are separated by a diaphragm and an anode chamber and a cathode chamber are formed, including solid alkali chloride in the anode chamber. A diaphragm alkaline chloride electrolysis method that supplies a saturated or nearly saturated aqueous alkali chloride solution. 2. While supplying a saturated or nearly saturated aqueous alkali chloride solution to the anode chamber, take out a portion of the anolyte from the anode chamber, add solid alkali chloride to it, and make it saturated or saturated, including the solid alkali chloride. As an aqueous alkali chloride solution,
The diaphragm method alkali chloride electrolysis method according to claim 1, wherein this is recycled to the anode chamber. 3 Using a filter diaphragm as a diaphragm, electrolysis is performed by supplying a saturated or nearly saturated aqueous aqueous alkali chloride solution containing solid alkali chloride to the anode chamber, and the electrolyzed solution obtained from the cathode chamber is evaporated. 3. The diaphragm method for alkali chloride electrolysis according to claim 1 or 2, wherein alkali chloride is precipitated and the precipitated alkali chloride is used as a solid alkali chloride present in an aqueous alkali chloride solution supplied to the anode chamber. 4. The diaphragm alkali chloride electrolysis method according to claim 1, wherein the solid alkali chloride has an average particle size of 10 to 300μ. 5 The weight of solid alkali chloride supplied per unit time is
The membrane method alkali chloride electrolysis method according to claim 1, wherein the weight is approximately equal to or less than the weight of dissolved alkali chloride electrolytically consumed per unit time in the anode chamber.