JPH0211677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement to an electrolytic cell, in particular an electrolytic cell for molten MgCl ₂ in which one or more bipolar intermediate electrodes are arranged between the anode and the cathode.

Many configurations have been proposed so far as electrolytic cells for producing metallic magnesium by electrolysis of molten MgCl ₂ . These basically consist of an anode made of graphite and a cathode made of an iron plate placed opposite one or two main surfaces of the anode, and one or more pairs of electrodes are placed side by side in the same electrolytic cell. or a structure in which one or more bipolar electrodes are sandwiched between a pair of these electrodes. The metallic magnesium produced during these operations usually has a lower density than the electrolytic bath and rises to the bath surface.
While it is necessary to recover this molten metal while preventing recombination due to contact with chlorine gas, which is a by-product rising in the bath, the spacing between the electrodes that produce these products should be kept as small as possible so that the current It is desirable to increase the efficiency and to arrange as many such electrode pairs as possible in the same electrolytic cell to increase the cell's production capacity.

The above technical demands are of contradictory nature, and although many electrolytic cell configurations have been developed and proposed to meet these demands, there is still no way to satisfy these demands at the same time. I haven't gotten what I wanted.

For example, some configurations are known in which many electrode pairs consisting of anodes and cathodes are arranged in one electrolytic cell to improve productivity per cell. For example, U.S. Pat. No. 3,676,323 describes an electrolytic cell in which a number of pairs of electrodes are attached, each of which is constructed so that both sides of a single iron plate are used as respective cathode surfaces for adjacent anodes. At this time, since no special measures are taken to prevent contact, there are many opportunities for the generated Mg and chlorine gas to recombine, resulting in low electrical energy efficiency. Furthermore, in particular, in a method in which the anode is fixed below the electrolytic cell, it is practically difficult to obtain adhesion between the anode material and the conductor, so that heat generation or power loss is likely to occur due to poor contact when electricity is applied. Moreover, there are drawbacks such as the need for complicated operations to replace the worn out anode material. On the other hand, US Pat. No. 3,907,651 similarly describes a configuration of multiple electrode pairs in which both sides of a cathode material are used opposite an adjacent anode. At this time, each cathode material placed in the electrolytic chamber is hollow, and a duct for passing the electrolytic bath therein is provided. Here Mg
When entering the duct from above, the electrolytic bath containing chlorine gas is separated and guided through an opening on the side of the duct to a metal Mg collection chamber separated from the electrolytic chamber by a partition wall, where Mg is collected in the bath. while the bath returns to the electrolytic chamber through an opening in the lower part of the partition wall. In this way, in this configuration, it is necessary to have a sufficiently large width for the duct inside the cathode material, so the distance between adjacent anodes placed between this cathode cannot be made too small. The number of electrode pairs and the capacity of the electrolytic cell are limited. Furthermore, especially in the case of the configuration shown in this publication, since there are a large number of electrodes (anodes) penetrating the lid of the electrolytic cell, it is technically quite difficult to hermetically seal the lid.

A structure with a reduced number of electrodes protruding from the electrolytic chamber as described above is described in US Pat. No. 2,468,022 and USSR Inventor's Certificate No. 609,778. In this case, multiple electrodes that are not externally connected are arranged in series between the anode and the cathode, and the surfaces close to the anode and cathode function as the cathode surface and the anode surface, respectively (bipolar electrode). ing. With such intermediate or bipolar electrodes, it is practically impossible to obtain a structure in which the graphite as the anode surface and the iron plate as the cathode surface are completely in contact with each other, so electrolysis progresses between these bonded surfaces and the cathode The surface may be worn out.

On the other hand, in the structure of the electrolytic cell described in U.S. Pat. No. 4,055,474, a plurality of anodes arranged side by side in the cell each have two surfaces inclined with respect to the vertical surface, and the cathode is approximately opposite to these surfaces. placed in parallel. In this case, it is expected that the current efficiency will improve by reducing the distance between the electrodes, but since the distance between the anodes cannot be reduced, there is a limit to improving the capacity of the electrolytic cell. The through-line arrangement leaves problems with hermetic sealing of the lid, as in the case of the above-mentioned US Pat. No. 3,907,651.

Accordingly, the present invention provides an electrolytic cell with a novel configuration that eliminates the drawbacks associated with the above-mentioned prior art. That is, the present invention effectively prevents the recombination of these products by quickly separating and recovering metal Mg and chlorine gas, and effectively reduces the voltage drop between the electrodes by reducing the electrode spacing. The purpose of the present invention is to provide an electrolytic cell that achieves improved current efficiency and improved production capacity per volume of the electrolytic cell. The subject matter of the present invention is to provide an essentially vertically oriented anode and a cathode, at least one bipolar intermediate electrode arranged between the pair of electrodes;
and an electrolytic chamber accommodating at least one electrode set consisting of the anode, cathode, and intermediate electrode, and a metal collection chamber separated from and attached to the electrolytic chamber by a partition having a through opening for electrolytic bath circulation. In the electrolysis device for ₂ , the intermediate electrode essentially connects the graphite material that provides the surface that functions as an anode and the iron material that provides the surface that functions as the cathode using a highly conductive material, and also connects the opposing surfaces of the two materials. a space is provided throughout the space, and at least one end of the space is connected to a through opening in the partition, so that a flow from the electrolytic chamber to the collection chamber for the metallic magnesium product is formed between the opposing members of the intermediate electrode. The present invention relates to an electrolytic cell for MgCl ₂ , characterized in that it comprises a channel.

Next, the present invention will be explained with reference to the accompanying drawings. FIG. 1 is a side cross-sectional view schematically showing an example of an electrolytic cell according to the present invention, FIG. 2 is a front cross-sectional view taken along the line A-A in FIG. 1, and FIG. FIG. 4 and FIG. 5 schematically illustrate several modified examples of the structure of this electrolytic cell, particularly of the intermediate electrode portion, by means of a side view and a plan view, respectively. It is. In each of these figures, an electrolytic cell 1 essentially consists of an electrolytic chamber 2 for carrying out an electrolytic reaction and a metal Mg collection chamber 4 separated from the electrolytic chamber 2 by a partition wall 3. The electrolytic chamber 2 has at one end an anode 5 consisting essentially of a graphite plate.
A cathode 6 made of iron plate is placed at the other end substantially perpendicular to the partition wall 3, and one end of both electrodes is connected to an external power source. The arrangement of both electrodes may be such that one electrode is placed in the center of the electrolytic chamber 2 and the other electrodes are placed at both ends, depending on the case. Between the anode 5 and the cathode 6, a plurality of bipolar intermediate electrodes 7 essentially made of graphite and iron are arranged substantially parallel thereto. These various electrodes 5, 6, and 7 are all mounted on a pedestal 8 made of electrically insulating material. The frame 8 is provided with a large number of through holes 9 for the flow of the electrolytic bath and sludge, while the floor of the electrolytic chamber 2 is sloped to collect the precipitated sludge. Each intermediate electrode 7 is provided with a cavity 12 for guiding a bath containing metal Mg generated between the graphite plate 10 and the iron plate 11 to the collection chamber 4, and this cavity 12 is connected to the partition wall 3. Open at the adjacent end and further partition wall 3
It communicates with the collection chamber 4 through a through hole 13 provided in the. As shown in FIG. 2, the intermediate electrode 7 is assembled to have a parallelogram cross section with the iron plate side facing upward, and is arranged approximately parallel to the anode having a tapered lower end. As will be described later, the intermediate electrode may take various other forms, such as those schematically shown in FIG. 4, for example. Generally, the intermediate electrode 7 is a thick graphite plate 10
and a support 14 such as a metal bolt or pin on this
It consists of a steel plate 11 attached via a. Pillar 1
4 is embedded in the iron-lead plate 10 at its lower end leaving a desired length, and the iron plate 11 is fixed to the head by welding or the like. In this way, the graphite plate and the iron plate of the intermediate electrode are provided with a space for bath flow between the inner surfaces of both members by the supports, and at the same time, the potential of both members is kept equal, while the outer surfaces of each are connected to the anode surface and the iron plate. Acts as a cathode surface. In this case, the entire cathode surface can be composed of a single iron plate or a plurality of horizontally or vertically long belt-shaped iron plates. The arrangement of each electrode is such that the anode and cathode are placed in the electrolytic chamber with their working surfaces upright, and between them is an intermediate electrode made of a single iron plate attached almost parallel to a graphite plate, with both outer surfaces upright. (Fig. 4-a), but in this case, while keeping the active surfaces of the graphite parts of the anode and intermediate electrode upright, the iron plate parts of the cathode and intermediate electrode are slightly tilted so that they do not overlap with the adjacent electrodes. It is also possible to open the interval slightly upwards (see b). Alternatively, as in the first example, the anode, cathode, and intermediate electrode graphite are arranged vertically, and the main part of the intermediate electrode iron plate except the upper end is installed almost upright, but the upper end is not connected. It bends from a certain height toward the graphite (c). This is particularly effective in separating chlorine gas and bath.
In each of the above examples, the iron plate may be formed as a single plate as a whole, but it may also be constructed by gathering vertically or horizontally long strip plates arranged horizontally or vertically. In the latter case, the joints of each shingle do not necessarily need to be sealed. Even if there are some gaps, the object of the present invention can be achieved. In short, any configuration is sufficient as long as the precipitated molten Mg rises steadily along the cathode surface.
Example (d) is a special case of the latter. In this case, a plurality of horizontally elongated strips are fixed to a single graphite plate at a certain angle of inclination to the opposite surface of the graphite plate, forming a Venetian blind or armor plate. It is showing. It is advantageous to provide an inwardly upward slope at the lower end of each iron piece in order to prevent recombination of Mg and chlorine gas. (a) to (d) above
In each of these examples and similar cases, the graphite and iron plates of the intermediate electrode can be arranged essentially parallel to each other, but the metallic Mg capture of this electrode A configuration in which the spacing increases continuously or stepwise toward the end outside the collection chamber is advantageous in creating a flow in the bath in this space toward the collection chamber.

These intermediate electrodes are submerged below the bath surface. A through hole 13 is provided in the partition wall 3 connected to each cavity 12 of the intermediate electrode 7 for guiding the bath to the collection chamber 4 . The cross section of the hole 13 is a rectangle or a parallelogram with almost the same width as the cavity 12, and the upper end is located at approximately the same height as the upper end of the intermediate electrode 7, but the entrance on the electrolytic chamber 2 side is slightly higher (but Below bath level) Collection chamber 4
By sloping downward toward the bottom, it is possible to effectively prevent chlorine gas from flowing into the collection chamber along with the bath. It is sufficient that the lower end of the hole 13 is higher than the pedestal 8 on which each electrode is placed. The thickness of the partition wall 3 can be made the same throughout, but by making one end of the electrolytic chamber 2, especially the anode side, thicker than the other end, it is possible to prevent stray current from occurring through the generated metal Mg. It is preferable to prevent this. On the other hand, on the top of the intermediate electrode, an insulating material block 15 with a height reaching above the bath level is placed over almost the entire width of the electrolytic chamber 2 in order to prevent short circuits due to metal Mg present near the bath surface. Good too.

The bath with metallic Mg flowing into the collection chamber 4 separates Mg on the bath surface and descends within the chamber. Natural convection may be used for this downward flow, but the outer circumferential wall of the chamber 4 may be thinned, cold air may be blown onto this outer wall, or refrigerant may be placed in a cooling pipe (not shown) immersed in the bath. If the temperature of the bath is lowered to a level that does not solidify by taking appropriate known cooling means such as passing through the bath, the downward flow of the bath will be accelerated, which is advantageous for the separation and recovery of metallic Mg. room 4
The Mg accumulated in the upper part of the tank is transported out of the tank as appropriate. On the other hand, the other product, chlorine gas, is recovered through a duct 16 provided above the bath level of the electrolytic chamber 2. The bath from which both of these products have been separated is passed through the opening 17 at the bottom of the partition wall 3 to the electrolytic chamber 2.
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The electrolytic bath can be introduced into the tank 1 in a conventional manner. For example, materials mixed to a predetermined composition are filled in the electrolytic chamber through the collection chamber 4 in a solid state or in a molten state.

Although the metal Mg collection chamber may be exclusively used in one electrolytic chamber, it is clear that a configuration in which it is shared by two or more electrolytic chambers is advantageous in that the equipment can be designed compactly.

Next, an example of operation of the electrolytic cell according to the present invention will be shown.

EXAMPLE An electrolytic cell configuration essentially as outlined in FIGS. 1-3 was used. An electrolysis chamber with a length of 1m, width of 2.28m, and depth of 2.2m.
0.2m x 2.21m x 2.2m (inner dimensions or more) metal Mg
The collection and cooling chamber is separated by a 35cm thick partition wall. The electrolytic chamber has a graphite plate with a height of 2 m, width of 1 m, and thickness of 12.5 cm, with one end serving as an anode, and the other end serving as a cathode.
An iron plate measuring 80cm x 1m x 3cm was placed. Between these is a graphite plate of 80cm x 1m x 12.5cm and 80cm x 1m x
Nine intermediate electrodes were arranged, each of which was connected to a 1.5 cm iron plate using 24 iron bolts with a diameter of 6 cm. At this time, the steel plate was fixed by welding the head of a bolt into the hole provided in the steel plate. Each of these electrodes is placed across the electrolytic chamber and placed on alumina brick stands arranged at intervals. The top of each intermediate electrode is 10cm wide x 20cm high x
A 1 m long alumina brick plate is placed so that it extends approximately 5 cm above the bath surface. Through-holes with the same width are provided in the parts of the partition wall that connect to each space with a width of about 4.5 cm formed between the iron plate and the graphite plate of the intermediate electrode. The lower end of each hole is 35 cm from the bottom of the intermediate electrode, the upper end is 15 cm higher than the top of the intermediate electrode at the entrance, and is sloped halfway at the same height at the exit on the collection chamber side. At the bottom of the partition wall, four openings with a cross section of 30 cm x 30 cm are provided for returning the bath to the electrolysis chamber.

In the electrolytic cell configured as above,
An electrolytic bath consisting of 20% MgCl ₂ , 50% NaCl, and 30% CaCl ₂ was melted, and the bath surface was adjusted to a height of 15 cm from the top of the intermediate electrode. A voltage of 38V was applied between the anode and cathode, and a voltage of 3.8V was applied between adjacent electrodes. While capturing the MgCl ₂ consumed by the reaction and recovering Mg from the electrolytic bath in the collection chamber, this bath is cooled by forcing cold air onto the outer wall of the electrolytic bath. The operation continued for 24 hours and 460Kg of metal Mg and 1.360Kg of Cl ₂ gas were recovered. The operating conditions are a bath temperature of 700℃ (electrolysis chamber), approximately 670℃ (bottom of the collection chamber), electrolytic current of 4500A, current density of 0.56A/ ^cm2 , current efficiency of approximately 94%, and power consumption of approximately 1 ton of Mg.
It was 8920KWH. This is compared to 14,000 to 18,000 KWH/t-Mg in the case of MgCl ₂ electrolysis using a conventionally commonly used single-cell type electrolytic cell, and also using an intermediate electrode with no bath flow path in between. This is a significant improvement compared to the 9425KWH/t-Mg that would have been achieved if the fuel had been used.

[Brief explanation of drawings]

FIG. 1 is a side sectional view schematically showing an example of an electrolytic cell according to the present invention, FIG. 2 is a front sectional view taken along line A-A in FIG. 1, and FIG. 3 is a plane cross-sectional view taken along line BB in FIG. 4 and 5 schematically illustrate a modified example of the structure of this electrolytic cell, particularly of the intermediate electrode, by means of a side view and a plan view, respectively. In the figures, each reference number represents the following member. 1... Electrolytic cell; 2... Electrolytic chamber; 3... Partition wall;
4... Metallic Mg collection chamber; 5... Anode; 6... Cathode; 7... Intermediate electrode; 8... Mount; 9... Mount through hole; 10... Graphite plate; 11... Iron plate; 12... …
Intermediate electrode cavity, 13... partition wall through hole; 14...
... Support column; 15 ... Insulation block; 16 ... Chlorine gas duct; 17 ... Partition wall opening.

Claims (1)

[Scope of Claims] 1. An electrode set consisting of an anode and a cathode arranged essentially vertically, at least one bipolar intermediate electrode arranged between the pair of electrodes, and the anode, cathode, and intermediate electrode. It has an electrolytic chamber that can accommodate at least one set, and a metal collection chamber that is separated from and attached to the electrolytic chamber by a partition wall that has a through opening for electrolytic bath circulation.
In the electrolyzer for _MgCl2 , the intermediate electrode essentially connects a graphite material that provides a surface that functions as an anode and an iron material that provides a surface that functions as a cathode using a highly conductive material, and also connects the opposing surfaces of the two materials. A space is generally provided between the electrodes, and at least one end of the space is connected to a through opening in the partition wall, so that between the opposing members of the intermediate electrode there is a flow from the electrolytic chamber to the collection chamber for the metallic magnesium product. An electrolytic cell for MgCl ₂ characterized by comprising a flow path. 2. The MgCl ₂ electrolytic cell according to claim 1, wherein the iron material of the intermediate electrode is an integral part. 3. The electrolytic cell for MgCl ₂ according to claim 1, wherein the iron material of the intermediate electrode is composed of a plurality of parts. 4. The MgCl ₂ electrolytic cell according to claim 1, wherein the iron material of the intermediate electrode is installed essentially parallel to the opposing surface of the graphite material of the adjacent electrode. 5. The MgCl ₂ electrolytic cell according to claim 1, wherein the iron material of the intermediate electrode forms a small upward slope with respect to the opposing graphite surface of the adjacent electrode.