JP2764125B2 - Electrolytic apparatus having electrode protection function and electrode protection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention detects an excessive rise in voltage in an electrolysis operation using an insoluble metal anode mainly at a high voltage higher than the breakdown voltage of the electrode substrate. An apparatus and method for protecting the insoluble metal anode.

(Conventional technology and its problems) In an electrolyzer requiring a high voltage, for example, an electrodialyzer, the total cell voltage depends on the number of elements in the electrolyzer.
It is about 100-200V. Current density is 10A even in seawater electrolyzer
/ For dm ² requires a voltage of about 5V per interelectrode distance 1cm Therefore interelectrode distance reaches a certain the 10V voltage at 2 cm. Further, in high-speed plating, the current density may be 100 A / dm ² or more, and in this case, the cell voltage in the sulfuric acid bath often exceeds 100 V. The electrode substrate of the insoluble metal anode used for these electrolysis is titanium or a titanium alloy, and its breakdown voltage in a halogen-free bath is about 100 V, and the breakdown voltage in a halogen-containing bath is about 10 V. is there.

When the insoluble metal anode is functioning normally, the potential of the anode is 1 to 2 V, and there is no problem with the electrode material or the electrode substrate. However, when the electrode material is consumed or when the electrode reaches the end of its life, the electrode is inactivated and the current hardly flows. In this case, in the electrolytic apparatus in which a plurality of cells are connected in series, most of the total cell voltage is applied to the portion having the highest resistance, that is, the passivated anode, and when the current becomes zero, the total cell voltage becomes the passive state. Will be hung on the converted anode. The voltage applied to the anode is 100 V in the case of a sulfuric acid bath,
Approximately 10 V for chlorine, depending on the type of halogen-containing bath
If the temperature exceeds the above, active dissolution of titanium or a titanium alloy as an electrode substrate is caused, and the electrode substrate cannot be used again as an electrode substrate.

In order to prevent such a state, a method of detecting a cell voltage and detecting a voltage concentration on an electrode substrate based on an abnormality of the cell voltage has been adopted. In normal electrolysis, the current is maintained at a substantially constant value, so if the resistance value of the electrolytic cell rises for some reason, the cell voltage rises, so this is a method of detecting an abnormality in the electrolytic cell by detecting the rise. . However, in practice, the cell voltage is not determined solely by the state of the anode. The cell voltage is determined as a combined value of many factors, such as the resistance of the cell. Therefore, by measuring the cell voltage, it is possible to detect an abnormality at a certain point in the entire electrolytic system, but the abnormality is not necessarily caused by the electrode. There is a disadvantage that the abnormality of the electrode is canceled by the abnormality and the cause of the fluctuation of the cell voltage cannot be determined. Further, for example, in the case of electrolysis containing a halogen element such as chlorine, the breakdown voltage is only about 10 V, and such a voltage may fall within the range of daily fluctuation in a dialysis tank. If specified, a slight change in the state of the electrode frequently stops the electrolysis, leading to a decrease in efficiency. There is a problem that the substrate cannot be destroyed.

In addition to the method of detecting the fluctuation of the cell voltage, a method of directly monitoring the anode potential has also been proposed. In this method, a reference electrode such as mercury sulfate or calomel is used, and a lugine tube is installed on the anode surface. It is to apply the usual laboratory method of measuring the anode potential by connecting these to a bridge circuit to a practical tank, and it is possible to perform precise measurement, but to measure or monitor continuously. There is a drawback that you can not.

(Object of the Invention) It is an object of the present invention to provide an apparatus and a method capable of quickly detecting an abnormality of an anode by measuring the potential of each anode instead of measuring the whole cell voltage.

(Means for Solving the Problems) According to the present invention, a conductive wire that is insulated from the insoluble metal anode and has corrosion resistance is installed near the insoluble metal anode, and a voltage difference between the anode and the wire is detected. When the voltage difference becomes equal to or more than a predetermined value, the power supply to the anode is stopped or the amount of power supply is reduced, and an electrolytic device having an electrode protection function and protection of an electrode using the device. Is the way.

 Hereinafter, the present invention will be described in detail.

The electrolysis apparatus having an electrode protection function and the electrode protection method according to the present invention are intended to detect abnormalities of the anode quickly and surely by measuring individual anode potentials instead of detecting the entire cell voltage. is there.

The voltage distribution in an electrolyzer is usually such that the equilibrium voltage required for the electrolytic reaction, the overvoltage and the voltage corresponding to a small ohmic loss are applied between the insoluble metal anode and the electrolyte in the vicinity, and the magnitude is accompanied by the generation of oxygen. Is 1.5 to 2.5 V based on a standard hydrogen electrode. Here, when the passivation of the anode occurs, the overvoltage or the voltage corresponding to the ohmic loss increases, and the potential difference between the liquid and the electrode increases. The potential difference is several mV to 1 V while the anode is operating in a normal or near normal state.
However, when the anode becomes inactive, the difference exceeds 1V.

What is to be achieved by the apparatus or the method of the present invention is to capture the passivation of the anode and prevent the electrode substrate from being destroyed due to voltage concentration caused by the passivation. Even in the electrolysis including the above, since the generation occurs in a region exceeding 10 V, it is sufficient to take a change of several V and take measures such as stopping the energization.

In order to catch such a large voltage change, it was found that the object can be achieved only by measuring the potential difference between the electrolyte and the anode without using a conventional potential measurement method using a reference electrode, and the present invention has been achieved. is there.

The device and the method of the present invention relate to the protection of the anode among the two electrodes of the electrolytic cell.As the anode, a so-called insoluble metal anode, which is usually coated on a base material of a valve metal such as titanium with an electrode material containing a noble metal or an oxide thereof. Although covered, the coating material is not particularly limited to these.

The conductive wire for measuring the potential difference between the anode and the electrolytic solution may be a normal conductive wire having corrosion resistance. Generally, a fine platinum wire is used, but of course, any other conductive material is used. May be. This wire must be installed in an insulated state from the anode. Usually, the wire is wrapped in a corrosion-resistant tube made of Teflon (trade name) or the like and installed in an electrolytic solution. The distance between the tip of the wire and the anode is not particularly limited,
If the distance is too close, the anode part to be detected is limited, and if the distance is too far, a variation factor occurs due to the resistance of the electrolytic solution itself, for example, the resistance due to bubbles. Therefore, usually about 1 to 10 mm is appropriate.
This distance is the distance between the anode surface and the body itself. If the wire is insulated with a corrosion-resistant material or the like as described above, the material may be fixed by contacting the anode to prevent fluctuation of the distance. This installation means is the most suitable for this.

The apparatus and method of the present invention are used as a normal electrolytic cell for salt electrolysis or the like or a dialysis tank for desalination or the like. When performing electrolysis by supplying current to a plurality of electrolytic cells with a single power supply, it is preferable to install the wire for each of a plurality of anodes and detect the occurrence of an abnormality in each anode.

In order to measure the voltage difference, the other end of the wire, one end of which is placed close to the anode, is appropriately pulled out of the tank, and a potential difference from the anode is measured by a voltmeter, a bridge circuit, or the like. Depending on the type of electrolyte, particularly the electrolyte containing halogen, when the measured value is several volts higher than the normal value, the power is turned off and the current is cut off, or the amount of current is reduced to abnormally. The voltage applied to the anode where the cracks occur is reduced to zero or greatly reduced to prevent damage or breakage of the anode. Instead of automatically controlling the power supply, a warning sound may be emitted when an abnormality is detected, and the power supply may be controlled manually.

When the potential difference of each anode is measured by the apparatus or method of the present invention and the fluctuation of the whole cell voltage is detected, not only the abnormality of the anode but also the abnormality of other parts of the electrolytic cell can be simultaneously detected, which is convenient. is there.

(Examples) Hereinafter, the present invention will be described with reference to examples, but the examples do not limit the present invention.

Example 1 A cation exchange membrane and an anion exchange membrane were installed in each unit tank of an electrodialysis tank having 70 unit tanks, and an insoluble metal anode coated with iridium oxide on the surface of a plate-like titanium substrate was used as an anode. Electrodialysis was performed using a nickel plate as a cathode and 10% sulfuric acid as an electrolyte. A 0.2 mm diameter platinum wire was inserted into a Teflon tube as a liquid voltage detection wire. A Teflon tube was further wound around the tip of the platinum wire, leaving a detection unit, and attached to the anode so that the outer diameter became 2 mm.

A voltmeter equipped with a voltage controller was installed to measure the voltage difference between the platinum wire and the anode, and the platinum wire was connected to the minus side and the anode was connected to the plus side. Since the normal voltage of the anode of the electrodialysis tank was 2 V and a fluctuation of about ± 0.5 V was expected, the control voltage was set to 5 V. When the voltage exceeded 5 V, the red lamp was turned on and the power was turned off.

After operating for 2000 hours under acceleration conditions, operation was continued under normal conditions. The total cell voltage was 135V. When normal operation was continued, the red lamp turned on and the power was turned off after 1300 hours of operation. When the anode was checked, the anode potential partially exceeded 3 V, and it was determined that the life was expired.
No abnormality was observed on the anode substrate itself.

Example 2 Desalination of the saline was carried out in the same manner as in Example 1 except that the number of unit cells was 30, the electrolyte was 3% saline, and the wire for liquid detection was separated from the anode by 5 mm. Was. The control potential was set to 3 V, and the anode current density was set to 2 A / dm ² .

When electrolysis was continued under these conditions, the total cell voltage fluctuated within the range of 60 to 75 V depending on the progress of electrolysis, and the voltmeter
1.8V was shown.

After approximately 3000 hours of operation, the voltmeter pointer begins to gradually rise
The power supply stopped after reaching 3V. When the anode was taken out, there was no change in appearance, but the potential of the coating increased by 1 V, indicating that the anode had reached the end of its life.

Comparative Example The same electrolytic cell as in Example 2 was prepared except that the wire for liquid detection was not installed, and salt water was desalinated under the same conditions as in Example 2.

After about 3000 hours of operation, the total cell voltage increased to 85 V, the current value decreased by half, and after a while, a white liquid began to flow from the anode chamber. When the power was turned off and the tank was disassembled, the coating on the anode surface was completely lost, and the anode substrate was corroded and ragged, and could not be reused.

(Effect of the Invention) The electrolysis apparatus having an electrode protection function and the electrode protection method according to the present invention detects the fluctuation of the whole cell voltage as in the related art when performing electrolysis using an insoluble metal anode, particularly under a high voltage. Instead, the potential difference between each anode and the electrolyte is measured to detect an abnormality.

Therefore, by measuring the anode potential determined only by the state of the anode without being affected by other factors such as the cathode and the diaphragm as in the related art, the abnormality of the anode can be detected quickly and reliably. Becomes possible. By taking appropriate measures such as stopping the power supply based on the detection, damage or breakage of the anode can be reliably prevented.

Claims (2)

(57) [Claims] 1. An insoluble metal anode, a conductive wire having corrosion resistance installed in the vicinity of the insoluble metal anode and insulated from the insoluble metal anode, a voltage detector for detecting a voltage difference between the anode and the wire. When the voltage difference detected by the voltage detector becomes equal to or more than a predetermined value, the electrode has a function of protecting the anode by stopping or reducing the amount of electricity to the anode. Electrolysis equipment. 2. A conductive wire, which is insulated from the insoluble metal anode and has corrosion resistance, is installed near the insoluble metal anode, and a voltage difference between the anode and the wire is detected and the voltage difference is equal to or more than a predetermined value. A method for protecting an electrode of an electrolysis apparatus, comprising: