JP3158996U - Electrolysis unit structure - Google Patents

Abstract

The present invention provides a bipolar electrolysis unit structure that maintains high current efficiency for use in an electrolytic cell for high-temperature molten salt electrolysis and that minimizes leakage current. An electrode group includes a side wall, an upper electrode frame, and a lower electrode frame. In the electrode group, a plurality of bipolar electrodes 2 having one surface as an anode and the other surface as a cathode and a plurality of end electrodes 1 whose electrode surfaces are only a cathode or an anode are parallel to each other with an inter-electrode distance. Be placed. The side wall surrounds the side surface of the electrode group. The upper electrode frame is installed on the upper part of the electrode group, and one end is flush with the anode surface of each electrode. The lower electrode frame is installed in the lower part of the electrode group, and one end is flush with the cathode surface of each electrode. [Selection] Figure 1

Description

The present invention relates to an electrolytic part structure for a bipolar electrolytic cell for obtaining a gas from an anode and a molten metal from a cathode by electrolysis by being immersed or placed in an electrolytic bath.

In an electrolytic cell that obtains gas from the anode and molten metal from the cathode by electrolysis from the high-temperature molten metal salt, it is necessary to completely immerse the electrode portion in the melt. That is, in the high-temperature molten salt, the molten salt melt itself is heated or maintained at a high temperature by good heat conduction and convection in the melt, but the heat conduction is poor in the gas phase on the melt and is usually heated. Therefore, apart from the surface in contact with the melt, the temperature is usually low, and the metal that is the electrolytic product and the electrolyte itself are solidified. When the electrode part is protruding in such a part, the metal produced | generated by electrolysis solidifies, it connects with the metal produced | generated in this way between electrodes, and it is often seen that it short-circuits. In order to avoid this, it is necessary to completely immerse the electrode portion in the electrolytic bath. On the other hand, in order to reduce the size of the electrolysis unit and further reduce the size of the electrolytic cell to prevent excessive heat dissipation and reduce energy consumption, a bipolar electrolytic cell that can be reduced in size and simplified in structure is desirable. The concern was how to reduce the leakage current. Further, in high-temperature molten salt electrolysis, it is almost impossible to put a diaphragm between the electrodes, and it is often seen that the efficiency in the reverse reaction is reduced due to the association between the anode product and the cathode product. In order to prevent this, it is necessary to provide a certain distance between the electrodes. Although there is a problem that a large inter-electrode distance usually increases the voltage and power consumption, it is not always a problem because of the need to use a heater to keep it at a high temperature, and it does not necessarily require enormous power consumption. Therefore, the distance between the electrodes in consideration of power consumption and current efficiency is necessary.

In this way, the bipolar electrolysis part is used by immersing it in the liquid, and further, it is necessary to increase the distance between the electrodes as much as possible, which is not necessarily disadvantageous in the case of molten salt electrolysis, On the other hand, the biggest problem under such conditions is a so-called leakage current in which a current is generated by skipping between the electrodes, and there is a problem that the efficiency is greatly reduced. How to reduce this has been a conventional problem. For this purpose, the inventors of the present invention have provided an electrode frame for regulating the current flow path above and below the electrode part of the bipolar electrolytic cell in Patent Document 1. Further, in Patent Document 2, since the leakage current depends on the maximum voltage supplied to the electrolytic cell, the electrode arrangement is reduced by reducing the number of bipolar electrolyzing units to create a large number of bipolar units and connecting them in parallel. It has succeeded in lowering the voltage and reducing the leakage current with a small electrode frame for preventing leakage current. However, even in these cases, if the distance between the electrodes increases, the current flow path provided in the electrode frame also expands accordingly, and it becomes necessary to increase the height of the electrode frame, and in order to prevent this, the distance between the electrodes is decreased. This time, there was a problem that the electrolytic current efficiency was lowered.

JP 2005-200759 A JP 2008-115455 A

An object of the present invention is to provide a bipolar electrolysis part structure that maintains high current efficiency mainly used in an electrolytic cell for high-temperature molten salt electrolysis and that minimizes leakage current.

The present invention is composed of a plurality of bipolar electrodes each having one surface as an anode and the other surface as a cathode, and a plurality of end electrodes each having only a cathode or an anode so that the electrode surfaces are substantially vertical. An electrode group disposed in parallel with a gap corresponding to the distance between the electrodes, a side wall surrounding the side surface of the electrode group, and an electrode width at a position corresponding to each gap between the electrodes disposed on the electrode group. An upper electrode frame having the same width and narrower than the gap between the electrodes, one end of the gap being flush with the anode surface and having a height, and corresponding to each gap between the electrodes installed at the lower part of the electrode group This is an electrolytic part structure comprising a lower electrode frame having a height that is the same width as the electrode width and narrower than the gap between the electrodes, and has a gap in which one end of the gap is flush with the cathode surface. As a result, the distance between the electrodes facing each other can be widened so as to minimize a decrease in current efficiency due to the anode and cathode electrolysis products meeting each other, and the cathode product is subjected to the liquid flow accompanying the anode gas. In this case, the anode product is prevented from rising above the electrode, and the anode product is prevented from falling due to the cathode product flowing down to prevent a decrease in current efficiency. It was possible to reduce the leakage current.
Further, if necessary, the lower end of the electrode frame along the liquid flow is chamfered so that the molten metal, which is a cathode product, is discharged to the lower portion, and the liquid flow is smoothly dropped downward. This is to prevent corners at the lower end because melt metal accumulates at the corners due to the surface tension of the molten metal, which may close the gaps in the electrode frame or lead to short circuits. is there. In addition, if the flow of the melt metal stagnates, the metal film on the cathode surface becomes thick, which may increase the leakage current through the portion, and this is also to prevent this.

In high temperature molten metal salt electrolysis, gas is usually generated at the anode as an anode product, and the cathode generates a molten metal. As a matter of course, the gas escapes upward while slightly spreading in the electrolyte along the anode surface, and the metal melt produced at the cathode is lighter in specific gravity than the electrolytic bath and may move upward in the electrolytic bath. Usually falls downward along the electrode surface, and further drops as a droplet from the lower end of the electrode. When the anode-generating gas and the cathode-generating metal associate with each other, they react therewith to form a metal salt again, which may cause a decrease in the apparent current efficiency. In order to prevent this, it is necessary to increase the distance between adjacent electrodes. That is, although it varies depending on the electrolytic bath or the electrolyte, for example, in molten zinc chloride electrolysis, if it becomes smaller than 3 to 5 mm, the current efficiency decreases significantly, so it is desirable to keep it at about 5 to 10 mm. Further, in order to keep the anode gas from separating from the anode surface as much as possible, it is desirable to slightly incline from the vertical so that the anode surface faces downward, and the angle is 0 to 10 degrees. If it is larger than this, outgassing will worsen and the electrical resistance will increase due to the gas. In addition, the cathode product may be held thick on the electrode surface, which may have an adverse effect.

On the other hand, the leakage current is determined by the size of the liquid resistance in the part formed by the gap between the electrode frames above and below the electrode and its height, so how to increase the liquid resistance, that is, reduce the cross-sectional area in the current direction. It depends on whether the height is increased. In this case, in order to increase the height of the frame, the electrode and the electrolysis part structure composed of these frames are increased. As a result, the depth of the electrolytic cell must be increased. It is desirable to do. That is, if the gas or melt metal flows and the cross-sectional area of the current flowing portion is halved, the height of the frame can be halved. Further, since one surface of the upper electrode frame is the same as the anode surface, the upper surface of the cathode surface is blocked in an eaves shape, and the cathode product is completely prevented from rising. The same applies to the lower electrode frame, and the anode gas does not go below the electrode frame, so that the current efficiency can be kept higher. Depending on these conditions, the optimum conditions for the gap between the electrodes and the gap of the electrode frame differ depending on the electrolytic condition electrolytic bath. However, in the direct electrolysis of zinc chloride, the distance between the electrodes is preferably 5 mm or more, and the electrode frame is considered to be out of gas. 2 to 3 mm was found to be desirable.

There is a possibility that current leaks through the melt metal, and for this, the lower end of the lower electrode frame on the cathode surface side is chamfered so as to promote the fall of the melt metal. Or it turned out that it can prevent by making a melt metal film thinner, by making the downward flow of a melt metal smooth by cutting round.

FIG. 4 is an elevational sectional view of the electrolysis unit structure, and a sectional view taken along the line a-a ′ of FIG. 3. FIG. 4 is an elevational cross-sectional view of the electrolysis unit structure, and is a cross-sectional view taken along line a-a ′ of FIG. 3 when the lower part of the electrode frame is chamfered. It is a top view of an electrolysis part structure. It is an example of the mode figure of the electrolysis part structure of this-application implementation.

The present invention will be described with reference to FIGS. In other words, the electrode group here is composed of an end electrode 1 having an anode or cathode only electrode surface having a current-carrying portion and a bipolar electrode 2 having one surface serving as an anode and one surface serving as a cathode. An electrode group is formed so that the surfaces are parallel with a gap. As shown in FIG. 4, the end electrode can be placed not only at the end of the electrode group but also in the middle, and this is also an end electrode in terms of function. FIG. 4 shows a structure in which two bipolar electrolysis units are connected in parallel. Here, the electrodes are inclined from the vertical plane, but they may be vertical. The upper electrode frame 3 is attached to the upper part of the electrode with a gap 6 in a portion corresponding to the electrode gap. One end of the gap between the electrode frames is on the same surface as the anode surface. The same applies to the lower electrode frame 4. The lower electrode frame 4 has a lower electrode frame having a gap opened so that the end surface is flush with the cathode surface. These electrode groups are surrounded by side walls 5. Examples will be described below.

An electrolytic part structure having an electrode group arranged as shown in FIG. 4 was assembled. That is, it has three end electrodes and is arranged so that the center is a cathode and both ends are anodes. The electrode was tilted 5 degrees so that the anode face was downward with respect to the vertical. This side surface was used as a side wall, and it was surrounded by a molded body in which porous zirconia having a thickness of 10 mm was impregnated with zirconia cement. This side wall has a groove for holding the bipolar electrode 2, and was fixed to the end electrode by a bolt made of silicon nitride. The side wall covered the entire side of the electrode group. As the electrode material, high-density graphite impregnated with resin, and further subjected to heat treatment, graphite carbon having a particularly high density was used. Here, it consists of 5 pairs of 5 electrodes, 2 pairs, 6 electrolytic units on one side, and a total of 12 electrolytic units. The distance between the electrodes was 10 mm, the height of the upper and lower electrode frames was 20 mm, and the gap between the electrode frames was 3 mm. The electrolytic part structure thus configured was immersed in an electrolytic bath and electrolyzed using a zinc chloride melt at 550 ° C. as an electrolytic solution, and the apparent current efficiency measured by the generated chlorine at a current density of 4000 A / m 2. Was 96%, and it was found that sufficient leakage current could be prevented. Here, when the electrode distance and the electrode frame gap were the same, the apparent current efficiency was 84%, and it was estimated that there was a large leakage current.

In the zinc reduction method, which is attracting attention for the production of ultra-high-purity silicon for solar cells, which is expected to expand significantly in the future, zinc is used as a reducing agent, and zinc is converted to zinc chloride. Since it is impossible with ordinary chemical methods, it is necessary to carry out all by electrolysis. In the future, it will be used very much for electrolysis.

DESCRIPTION OF SYMBOLS 1 End electrode 2 Bipolar electrode 3 Upper electrode frame 4 Lower electrode frame 5 Side wall 6 Electrode frame gap 7 Electrolytic power source / cathode 8 Electrolytic power source / anode

Claims (4)

The electrode surface is composed of a plurality of bipolar electrodes having one surface as an anode and the other surface as a cathode, and a plurality of end electrodes each having only a cathode or an anode, and these electrodes are connected to each other. The electrode group arranged in parallel with a gap corresponding to the distance, the side wall surrounding the side surface of the electrode group, and the same width as the electrode width at a position corresponding to each gap between the electrodes installed on the electrode group An upper electrode frame that is narrower than the gap between the electrodes and has a height in which one end of the gap is flush with the anode surface, and a position corresponding to each gap between the electrodes that is installed at the bottom of the electrode group An electrolytic part structure comprising a lower electrode frame having the same width as the electrode width, narrower than the gap between the electrodes, and having a gap in which one end of the gap is flush with the cathode surface. 2. The electrolytic part structure according to claim 1, wherein the electrode surface is disposed with an inclination of 0 to 10 degrees from vertical so that the anode surface faces downward. The gap corresponding to the distance between the electrodes is 5 to 10 mm, and the gap between the electrode frames above and below the gap is 2 to 5 mm. 2. The electrolytic part structure according to claim 1, wherein the lower end of the gap that is flush with the cathode surface of the lower electrode frame is chamfered.

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