JPS61194190A - Method and device for reducing reverse current - Google Patents

Abstract

PURPOSE:To suppress the increase in running cost arising from the generation of reverse current and to reduce electric power consumption by discharging the electrolyte in an electrolytic cell disposed with an anode and cathode from the cell at the same instant when the electrolysis is suspended. CONSTITUTION:The electrolyte is fed via a supply pipe 1 to the electrolytic cell 2 where electrolysis is effected by the anode 3 and cathode 4. The electrolyte is taken out of a discharge pipe 5. The current flows from a current rectifier 6 to the electrolyte via the anode 3 and returns to the rectifier 6 via the cathode 4. A pipe 19 provided with a solenoid valve 18 is attached to the lower part of the electrolytic cell 2 and the valve 18 is connected via an electric line 20 to the rectifier 6. The valve 18 opens and the electrolyte in the cell 2 is discharged through the pipe 19 when the output from the rectifier 6 is turned off.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a thin film type oxide anode arranged in various electrolytic cells,
The present invention relates to a method for reducing reverse current that prevents damage caused by reverse current flowing from a cathode to an anode via an electrolyte, and an apparatus for implementing this method.

[Conventional technology]

Conventionally, electrolysis of various solutions (seawater electrolysis, saltwater electrolysis).

(soda electrolysis, etc.) is carried out by the method shown in Fig. 8. In the figure, the electrolytic solution enters an electrolytic cell 2 through an electrolytic solution supply pipe 1, is electrolyzed at an anode 8 and a cathode 4, and is sent to the next tube station through an electrolytic solution discharge pipe 5. The current at this time flows from the rectifier 6 through the current-carrying line 7, from the positive WiB to the cathode 4 via the electrolyte, and returns to the rectifier 6 via the current-carrying line 8.

By the way, the power consumption of the installed cathode and anode,
Current efficiency for the anode.

These include potential, lifespan, etc., but in particular, the performance of the anode greatly influences the performance of the electrolyzer.

In the past, the main anode used for these electrolysis was Ti.
-Pt (electroplated), but now thin-film oxide electrodes are becoming mainstream as energy-saving and cost-saving electrodes. This thin film type oxide electrode is generally called D8A (dimensionally stable anode), and is made of Ti as a base material and Pt on top of it.
, Ir, Ru.

A small amount of base metal is mixed into a noble metal such as Pd, which is coated and fired. These D S A t-Ti-Pt
The electrical properties (current efficiency, anode potential, etc.) are particularly excellent when compared to .

[Problem that the invention seeks to solve]

However, as research on D8A characteristics progresses, it has recently become clear that if the anode is immersed in an electrolyte without energizing, oxides may form due to corrosion of the anode alone or a reverse current caused by the potential difference with the cathode. Problems such as metal reduction occurring and increased consumption became clear. In particular, when an electrode and an anode are present on one base material or when the cathode and anode are short-circuited, the amount of consumption of the anode coating material increases rapidly. These will be explained below with reference to the drawings.

(1) Corrosion of the anode alone Figure 4 (a), (+==r) shows the state when the K anode is immersed alone. FIG. 4-(A) shows the state at the initial stage of energization, in which the positive Wi 3 is immersed in the electrolytic solution 9. The anode 8 is made of titanium 10 and metal oxide 11. Here, if the various metal oxides contained in the metal oxide 11 are M+, Ml, and MS, since these metal oxides are integrated as a solid solution, the potential difference on the surface in contact with the electrolyte 9 is as follows. It is not that big, so it can be considered that corrosion will not progress easily. However, with the passage of 2 days of energization, Fig. 4-(
When a worn point 12° 1B as shown in b) is formed, the surface potential of the metal oxide 11 will be.

A potential difference occurs between the unused part and the worn part.

This is because there is a difference in the performance of M+, Hz, and Ms, and a difference occurs in the amount of consumption due to energization. Here 2
The order of corrosion resistance against energization is ′M+ >Ml
)Ml, and if the order of the potential of the oxide alone is Ml)Mt)Ms noble and base, then the potential difference between the consumed part 12.18 and the unconsumed part is from the state in Figure 4-(a). The large area where the corrosion current enters (the culprit area) is consumed by the reduction current.

(2) Corrosion when the cathode and anode are connected through a rectifier: Consider the case where a rectifier is connected to the anode W18 and the cathode 4 as shown in FIG. Let the potential of the anode 8 during electrolysis be El, and the potential of the cathode 4 be Ex.

between the negative and anode when the rectifier is turned off.

E=E凰−Ex (“, ° Ex(0)
There is a voltage load of Then, a reverse current flows from the cathode 4 to the anode 8, and the anode 3 is reduced. The magnitude of this reverse current depends on the rectifier resistance, electrolyte resistance, and electrode area.
The curve will look like the one shown in the figure. Also, the curves are A, B
.

It can be divided into eight areas. Here, the area A is the anode 8
→ Rectifier 6 → In the reverse current region where the current to the negative Wi4 is suppressed by the resistance of the rectifier 6, the potential difference between the anode 8 and the cathode 4 remains in equilibrium for a short period of time. Region B is the potential difference between the positive Wi8 and the negative electrode 4. The region where the reverse current also decreases as the
Region C is a reverse current generated by the difference in natural potential between positive Wi8 and negative Wi4. The positive I#iS is consumed by the reverse current (reduction current) thus generated.

(3) When the cathode and anode are short-circuited or when the cathode and anode are on one substrate: When the cathode and anode are short-circuited as shown in Figure 6-(a),
B) and (C) show a state in which a cathode and an anode are present on one base material.

In Figure 6-(a), the anode 8 and cathode 4 are connected to the lead wire 1.
4 is shorted. FIG. 6-(b) shows the anode side 10 (front surface) on one electrode plate 15.

This shows the electrode immersed in the electrolyte 9 when there is a cathode side 11 (back side).
5 shows a state in which an electrode having an anode portion 16 and a cathode portion 17 on the same side is immersed in an electrolytic solution 9.

Comparing these three states (a), (b), and (c) with the state in which the rectifier is used in (2) above, the amount of reverse current flowing within a unit time increases due to the lack of resistance of the rectifier. FIG. 7 shows the relationship between the reverse current and the time elapsed since the power was turned off in the state shown in FIG. 6-(a).

Next, we conducted the following tests to determine how the electrical characteristics and amount of wear of the electrodes change in each state of (1) to (3) (see Figures 3, 4, and 6). We conducted tests and investigated the conditions and methods.

Anode area: 80mm x 4Gmm (Pt, Pd main components) Distance between cathode and anode: 8mm, cathode: titanium electrolyte:
Seawater electrolyte temperature: around 25°C Current density: 15 A/'♂ Power off time: I Ho+1r Power off frequency: 1 time/day Electrolyte flow rate: 0.1 rr1/see test method: 1
Turn on the power at 5A/d♂ and turn off the power only once/day x IHour.

As a result, the relationship between consumption I and the number of times the power was turned off is shown in Figure 8, and the relationship between current efficiency and the number of times the power was turned off is shown in Figure 9.
FIG. 10 shows the relationship between the anode potential and the number of times the power was turned off. It stopped after turning off the power 62 times.

In these figures, 2 curves 1 are 2 curves 2 when only electricity is applied.
2 is the corrosion of the anode alone.Curve 3 is the case where the cathode and anode are connected through a rectifier.

Curve 4 shows the change when the anode and cathode are short-circuited.

Song ts4 was consumed by 75% after 62 short circuits, the current efficiency was about 97% at the beginning, but it decreased to 80%, and the potential was 1.1
The voltage increased from 8V to around 1.5V.

When the performance of the anode is degraded in this way, a first-order problem arises.

(a) Running costs increase as current efficiency decreases and potential increases.

(b) Due to increased consumption, the electrode life becomes shorter.

In addition, in various electrolytic cells, the frequency of discontinuing electrolysis while the electrolytic solution remains in the tank is high (although it differs slightly depending on the type of electrolysis), and there is an urgent need to solve the above problem.

The present invention has been made in view of the above circumstances.

It is an object of the present invention to provide a method and a device that can suppress an increase in running costs and an increase in electrode consumption due to the generation of reverse current.

[Means for solving problems]

The method of the present invention aims to reduce the increase in running costs caused by the generation of reverse current and the amount of electrode wear by draining the electrolyte in the electrolytic cell containing the anode and cathode at the same time as electrolysis is stopped. be.

The apparatus of the present invention is an apparatus for carrying out the method of the present invention, in which an electrolytic cell is provided with an anode and a cathode, an electrolytic solution discharge pipe is provided at the bottom of the electrolytic cell, and the electrolytic cell discharge pipe is The present invention relates to a reverse current reducing device characterized in that a solenoid valve electrically connected to a rectifier is disposed in a flow path.

[Effect]

In the method of the present invention, the electrolytic solution in the electrolytic cell is discharged to the outside of the electrolytic cell at the same time as electrolysis is stopped, thereby eliminating the occurrence of reverse current between the cathode and the anode.

This solves the above-mentioned problems, and the device of the present invention is a device for carrying out the method of the present invention, by operating the electrolyte discharge pipe and the solenoid valve.
This makes it possible to easily discharge the electrolytic solution out of the electrolytic cell at the same time as stopping electrolysis.

〔Example〕

Next, a first embodiment of the present invention will be described with reference to FIG.

In this embodiment, a pipe 19 equipped with a solenoid valve 18 is attached to the lower part of the electrolytic cell 2.
0 to the rectifier 6. Here, the electromagnetic valve 18 is closed during electrolysis, and is opened at the same time as the output of the rectifier 6 is cut off, so that the electrolytic solution in the electrolytic cell 2 is discharged.

With the above configuration, a test was conducted using seawater as an electrolyte under the same conditions and method as the test described in the conventional method section, and changes in consumption and electrical performance were investigated. The results are shown in the table below. Note that the sample names used in each test are A and B, and the conditions are shown below. Separate corrosion tests were not performed.

A: The cathode and anode are connected through a rectifier.

B: Table when cathode and anode are short-circuited However, the values in the above table are the measured values after the power was turned off 64 times.

As is clear from this result, when a rectifier is used, there is no wear and tear, and no deterioration of electrical characteristics occurs. Furthermore, the consumption when the cathode and anode were short-circuited was 5%, which was 1/15 of the consumption when the electrolyte was not discharged, and the electrical characteristics deteriorated only slightly.

Here, the effects of discharging the electrolyte in the electrolytic cell are summarized below.

(1) It has become possible to significantly reduce consumption.

(2)! Stops the progress of deterioration of electrical characteristics (current efficiency and potential).

(3) As a result, increases in running costs are suppressed.

Next, a second embodiment of the present invention will be described with reference to FIG. This embodiment is a diagram of a device in which the electrolyte is sent from the electrolyte supply pipe 1 even after the output power of the rectifier 6 is turned off.

In the figure, a solenoid valve 21 is provided in the supply pipe 1, located near the electrolyte inlet of the electrolytic cell 2, and connected to the rectifier 6 via an electric line 22.

In addition, the solenoid valve 2B is provided in the seawater discharge pipe 5, and the electrolytic cell 2
The rectifier 6 and the electric line 24 are located near the electrolyte outlet of the
connected via. moreover.

The supply pipe 1 and the discharge pipe 5 are communicated through a bypass pipe 26 equipped with a solenoid valve 25 , and the solenoid valve 25 is connected to the rectifier 6 via an electric line 27 . In this figure,! During disassembly, solenoid valves 21 and 23 are open, and solenoid valve 18.2
5 is in the closed state. At this point, when the output power of the rectifier 6 is turned off, the solenoid valves 21 and 28 are closed, and the solenoid valve 18.2 is closed.
5 opens. The electrolyte then enters the discharge pipe 5 via the bypass pipe 26 without entering the electrolytic cell 2 and is sent to the next location. At this time.

The electrolyte in the electrolytic cell 2 is discharged from the pipe 19 to the outside of the cell,
By reducing the flow of reverse current into the anode 8, the same effects as in the first embodiment can be obtained.

By attaching a motor pump to the pipe 19 equipped with the electromagnetic valve 18 described in the two embodiments 1 and 2, it is also possible to quickly drain the electrolyte in the electrolytic cell 2. However, if a motor pump is installed, a floatless switch or the like must be provided at the same time so that the power to the motor pump can be turned off when the electrolyte in the electrolytic cell 2 runs out.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to significantly reduce the amount of electrode consumption, prevent deterioration of electrical characteristics, and suppress increases in running costs compared to the conventional method. It is a simple and inexpensive device, and has the advantage that the electrolyte can be quickly discharged from the electrolytic cell at the same time as electrolysis is stopped.

[Brief explanation of drawings]

1 and 2 are schematic configuration diagrams showing the first and second embodiments of the device of the present invention, FIG. 3 is a schematic configuration diagram showing an example of a conventional electrolysis device, and FIG. ) and (b) are explanatory diagrams showing unconsumed anodes and consumable anodes immersed in an electrolytic solution, FIG. 5 is a diagram showing changes over time in the reverse current flowing from the cathode to the anode via the rectifier, and FIG. 6 - (A) is an explanatory view showing a state in which the cathode and the anode are short-circuited and immersed in an electrolytic solution. Figures 6 (b) and (c) are explanatory diagrams showing a state in which an electrode in which a cathode part and an anode part are present in one electrode is immersed in an electrolyte, and Figure 7 is an output power supply of a rectifier. The cathode and anode are short-circuited at the same time as the current is turned off, and the graph showing the change over time of the reverse current flowing at this time is shown in Figure 8.
A diagram showing how the amount of anodic oxide consumption when the power is turned off by y x 1 tfour changes depending on the number of times the power is turned off. Figure 9 is a diagram showing how the current efficiency of the anode changes with the number of times the output power of the rectifier is turned off, and Figure 1θ is a diagram showing how the potential of the anode changes with the number of times the output power of the rectifier is turned off. It is. 1... Electrolyte supply pipe, 2... Electrolytic cell 93... Anode. 4... Cathode, 5... Electrolyte discharge pipe, 6... Rectifier, 7° 8... Electric wire circuit, 9... Electrolyte, 10.
... Base material (titanium), 11... Oxide, 12.18
... Consumable part, 14... Short circuit wire, 15... Electrode plate, 16... Anode part, 17... Cathode part. 18... Solenoid valve, 19... Pipe, 20... Electric line circuit, 21... Solenoid valve, 22... Electric line circuit,
23...Solenoid valve, 24...Electric line circuit, 25...
Solenoid valve, 26... bypass pipe, 27... electric line circuit. Number 10

Claims (2)

[Claims] (1) A method for reducing reverse current in an electrolytic cell equipped with an anode and a cathode, which comprises turning off the output power of a rectifier and stopping electrolysis, and at the same time draining the electrolyte in the electrolytic cell. (2) In the above method in which an anode and a cathode are arranged, an electrolyte discharge pipe is provided at the bottom of the electrolytic cell, and a solenoid valve electrically connected to a rectification path is provided in the electrolytic cell discharge pipe. A reverse current reduction device characterized by: