JPS6240438B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electric circuit for stopping operation of an electrolytic cell of an ion-exchange membrane electrolyzer. More specifically, when stopping the electrolytic cell of a cation exchange membrane electrolyzer using a mobile jumper switch, the life of the anode of the electrolytic cell can be extended by keeping the voltage drop in the jumper switch circuit above a certain value. This relates to an electric circuit when the electrolytic cell is stopped. Conventionally, there are two methods for electrolyzing an aqueous alkali metal chloride solution: the mercury method and the diaphragm method.
Furthermore, an ion exchange membrane method using an ion exchange membrane as a diaphragm has been developed and put into practical use. In Japan, from the perspective of preventing environmental pollution caused by mercury, a shift from mercury laws to mercury-free laws is being implemented under the guidance of the government. Non-mercury electrolysis methods are broadly divided into diaphragm methods, which mainly use asbestos, and ion exchange membrane methods, which use cation exchange membranes. When stopping the operation of one electrolytic cell that has many diaphragm electrolytic cells electrically connected in series, connect a mobile jumper switch in parallel to the electrolytic cell to be stopped and close the jumper switch. , all the electrolytic current flowing in the electrolytic cell is passed through the jumper switch circuit, and the operation of the electrolytic cell is stopped. Even after the electrolytic cell is stopped, an aqueous alkali metal chloride salt solution is supplied to the electrolytic cell to replace the caustic alkali in the cathode chamber with the supplied aqueous alkali metal chloride solution, and the caustic alkali flows back into the anode chamber and replaces the caustic alkali in the anode (metal anode). This prevents deterioration due to
Also, when stopping the operation of one electrolytic cell with mercury method electrolysis that is electrically connected in series,
The electrolytic cell short-circuit switch attached to the electrolytic cell to be stopped is closed, and all the electrolytic current flowing in the electrolytic cell is passed through the short-circuit switch circuit, thereby stopping the operation of the electrolytic cell. By supplying the salt water alkali metal salt aqueous solution and/or continuing the circulation of mercury even after stopping the electrolytic current in the electrolytic cell, the mercury amalgam is decomposed in the decomposition tower, and the mercury metal is circulated to the electrolytic cell. , prevents deterioration of the anode (metal anode) due to caustic alkali. On the other hand, even in ion-exchange membrane electrolyzers that have been developed and put into practical use in recent years, especially in monopolar ion-exchange membrane electrolyzers, it is difficult to operate one electrolyzer in a group of electrolyzers that are electrically connected in series. When stopping, a mobile jumper switch is connected in parallel to the electrolytic tank to be stopped, the jumper switch is closed, and all the electrolytic current flowing in the electrolytic tank is passed through the jumper switch circuit. , stop the operation of the electrolytic cell. The aqueous alkali metal chloride solution is continued to be supplied to the electrolytic cell even after the electrolytic current stops flowing, and the anode (metallic This prevents deterioration of the anode). However, when stopping the operation of one electrolytic cell in a group of cation-exchange membrane electrolytic cells electrically connected in series, the inventors installed a mobile jumper switch on the electrolytic cell to be stopped. When the electrolytic cell is connected in parallel with the electrolytic cell, the jumper switch is closed, and all the electrolytic current flowing in the electrolytic cell is passed through the jumper switch circuit, and the operation of the electrolytic cell is stopped, the voltage from the electrolytic cell is It was discovered that a large loop current flows through the jumper switch circuit. As a result of intensive studies to elucidate the cause of this phenomenon, the present inventors found that if the electrolytic current of the cation-exchange membrane electrolytic cell in operation is stopped without using a short-circuit switch, the anode It was discovered that an electromotive force was generated between the cathode and the anode so that the anode became positive, and that more oxygen was generated in the anode gas during restart. The magnitude of the electromotive force varies depending on the electrolytic tank liquid temperature and catholyte concentration (caustic alkali metal concentration), but is 0.7V to 2.4V per tank.
reach. The cause of this starting force is not clear, but it is thought to be due to reduction of the coating material of the metal anode or elution of the cathode metal material. On the other hand, it is also possible that the gas adhering to the anode and/or cathode is dissolving and discharging. Since the voltage drop in a mobile jumper switch circuit is generally about 0.3V to 0.6V, it is obvious that if the starting force of the electrolytic cell is 0.7V to 2.4V, a current will flow through the jumper switch circuit, and the electromotive force will be It is fully believed that the cause of this is due to the reduction of the anode coating material and/or the elution of the cathode material, so if this state continues for a long time, the life of the anode and/or cathode will be shortened. As a result of studying methods to prevent such loop currents, the present inventors decided to stop the operation of one electrolytic cell in a group of cation exchange membrane electrolytic cells electrically connected in series. By inserting a resistor into the jumper switch circuit in series with the mobile jumper switch to make the voltage drop in the jumper switch circuit 0.7V or more, more preferably 2.4V or more, the electromotive force of the stopped electrolytic cell can be reduced. It has been found that loop current caused by this can be prevented. For a more detailed understanding of the invention, reference is made to the accompanying drawings. FIG. 1 is a diagram showing the electrical connection method of a conventional electrolytic cell, where 1-1, 1-2, ..., 1-n are electrically connected in series by a bus bar 6. This is a membrane method electrolytic cell, and is operated by being supplied with electrolytic current from a rectifier 2 through bus bars 4 and 5. When stopping the operation of one electrolytic cell, for example 1-2, in these electrolytic cell groups, the mobile jumper switch 3 is connected in parallel with the electrolytic cell 1-2, and the lead busbars 7 and 8 of the jumper switch are connected. By connecting to the inter-electrolytic cell bus bar 6 with a bolt and closing the jumper switch, the entire electrolytic current flows through the jumper switch and the operation of the electrolytic cell 1-2 is stopped. At this time, when an electromotive force is generated in the electrolytic cell 1-2 and its magnitude is larger than the voltage drop of the jumper switch circuit, the current due to the electromotive force is transferred from the electrolytic cell 1-2 → bus bar 7 → jumper switch 3 → It will flow through a closed loop circuit from bus bar 8 to electrolytic cell 1-2, and the anode and/or
Or, it is thought that it is a cause of deterioration of the cathode. 2 and 3 are diagrams showing the electrical connection method of the electrolytic cell of the present invention. In FIG. 2, a resistor 9 is inserted in series with the jumper switch circuit to reduce the voltage drop of the jumper switch circuit. This is a method of stopping an electrolytic cell in which the electromotive force of the electrolytic cell 1-2 is made larger than the electromotive force of the electrolytic cell 1-2 to prevent a current from flowing due to the electromotive force of the electrolytic cell 1-2. The resistor 9 may be provided separately in series with the jumper switch, or the resistance of the lead busbars 7, 8 of the jumper switch itself may be increased. In the method of stopping the electrolytic cell shown in FIG. 2, all of the electrolytic current flows through the jumper switch circuit, so that the power loss caused by the insertion resistor 9 while the electrolytic cell is stopped is large and uneconomical. In FIG. 3, since power loss is large in the electrolytic cell stop method using the jumper switch shown in FIG.
After disconnecting the electrical connection between the electrolytic cell bus bar 6 and the electrolytic cell bus bar 6, the jumper switch 11 is closed and the flow of electrolytic current is changed from the electrolytic cell 1-1 to the bus bar 6 to the bus bar 7.
→ Resistor 9 → Busbar 10 → Jumper switch 3
→ Busbar 8 → Busbar 6 → Electrolytic cell 1-3 (not described) to Electrolytic cell 1-1 → Busbar 6 → Busbar 7 → Busbar 12 → Jumper switch 11 → Busbar 13 → Busbar 10 → Jumper switch 3 → Busbar 8 By changing → bus bar 6 → electrolytic cell 1-3 (not shown), power loss due to resistor 9 can be reduced. Example 1 A small electrolytic cell measuring 5 cm x 5 cm was used, the anode was made of titanium coated with ruthenium oxide, the cathode was made of stainless steel, and an ion exchange group was placed between the anode chamber and the cathode chamber. An electrolytic cell using a carboxylic acid type fluorine-based cation exchange membrane was operated under the following conditions, and the electromotive force when the operation was stopped is shown in Table 1. Operating conditions Current density: 20A/dm ² Supply brine concentration (salt): 310g/ Electrolyzer temperature: 90℃ Caustic alkali concentration (NaOH): 40%

[Table] Example 2 Using the same electrolytic cell as in Example 1, Table 2 shows the electromotive force of the electrolytic cell when the salt water in the anode chamber was replaced with the supplied salt water after the operation was stopped.

[Table] Example 3 In Example 1, the electromotive force was
When the voltage is 1.5V, create a short circuit as shown in Figure 1,
The current flowing through the short circuit when the short circuit switch was closed was as shown in Table 3. Additionally, the pH of the anolyte dropped dramatically upon restart.

[Table] Example 4 In Example 2, the electromotive force was
When the voltage is 1.5V, create a short circuit as shown in Figure 1,
When the short circuit switch was closed, the current flowing through the short circuit was as shown in Table 4. Additionally, the pH of the anolyte dropped dramatically upon restart.

[Table] As shown above, when the voltage drop on the short circuit side is small, a reverse current of varying magnitude will flow into the electrolytic tank depending on the electromotive force of the electrolytic tank, and the larger the reverse current, the more it will affect the anode coating material. It turns out that there is a large amount. Example 5 In Example 3, the electrolytic cell was stopped using the electrical connection method shown in FIG. The resistance inserted into the short circuit is approximately 0.14Ω, and the voltage drop in the short circuit is approximately 0.7V.
It was hot. The current flowing through the short circuit at this time is shown in Table 5.
It was hot on the street. Furthermore, the pH of the anolyte upon restart was almost unchanged from before the shutdown.

[Table] As described above, the method of the present invention has made it possible to significantly reduce short circuit current.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram of a conventional electrolytic cell. FIG. 2 is an electrical connection diagram of the electrolytic cell of the present invention. FIG. 3 is an electrical connection diagram of another electrolytic cell of the present invention.

Claims (1)

[Claims] 1. When stopping an electrolytic cell divided into an anode chamber and a cathode chamber by a cation exchange membrane using a mobile jumper switch, a resistor is inserted into the jumper switch circuit to shut down the jumper. An electric circuit when the electrolyzer is stopped, characterized in that the voltage drop in the switch circuit is 0.7V or more. 2. The electric circuit when the electrolytic cell is stopped according to item 1, characterized in that another jumper switch is provided in parallel with the resistor to short-circuit the resistor inserted in the jumper switch circuit. 3. The electric circuit when the electrolytic cell is stopped according to item 1, wherein the resistance inserted in the jumper switch circuit is the resistance of the electric conductor itself of the jumper switch circuit.