JP2006028567A - Bipolar electrolytic cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bipolar electrolytic cell where bipoles and refractory mounts supporting the bipoles have engaged structure so as to prevent the positional deviation of the bipoles from the refractory mounts supporting the bipoles. <P>SOLUTION: (1) Regarding the electrolytic cell for molten magnesium chloride having bipoles, the lower parts of the bipoles and the upper parts of refractory mounts supporting them have engaged structure. (2) Regarding the bipolar electrolytic cell in the above (1), the lower parts of the bipoles are provided with recessed grooves, and the upper parts of the refractory mounts are provided with projecting bulged parts. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolytic cell for molten magnesium chloride, and more particularly to a structure of a bipolar electrolytic cell that electrolyzes molten magnesium chloride and recovers metallic magnesium and chlorine gas.

When titanium tetrachloride and metal magnesium (Mg) are subjected to a reduction reaction to produce metal titanium, molten magnesium chloride is generated as a by-product. The produced molten magnesium chloride is charged into an electrolytic cell and mixed with CaCl ₂ , NaCl, MgF _2, etc. to form a molten salt, and chlorine gas and cathode generated by electrolysis at the anode of the electrolytic cell It is separated into Mg produced at (cathode). Usually, the recovered chlorine gas is used again for the production of titanium tetrachloride, and Mg is used for the production of titanium metal again.

  The bipolar electrolyzer can improve productivity because it increases the number of electrodes as electrodes that generate Mg and chlorine gas during the above electrolysis by arranging a bipolar electrode between the anode and the cathode. in use.

  As shown in FIGS. 1 and 2, which will be described later, the bipolar electrolytic cell is divided into an electrolysis chamber 2 and a metal accumulation chamber 3, and a refractory wall 4 and a curtain wall 5 are provided therebetween, and a lid 6 It has a sealed structure. In the electrolysis chamber 2, the anode 7 and the cathode 8 are respectively fixed to the furnace wall 9 and the lid 6 made of refractory through an electrically insulated seal structure. Eight electrode portions are placed on the refractory bases 10 and 11.

  Further, in this structural example, two bipolar electrodes 12 and 13 are placed on the refractory bases 14 and 15 at a predetermined interval, for example, 5 to 25 mm, between the electrode portions of the anode 7 and the cathode 8. ing. These refractory pedestals 10, 11, 14 and 15 are fixed to shelves 16 and 17 provided on the furnace wall 9 and the refractory wall 4 by insulating blocks 18 having a predetermined width, respectively.

  Further, the bipolar electrodes 12 and 13 have a structure in which the electrodes 7 of the anode 7 and the cathode 8 and the bipolar electrodes 12 and 13 are held at predetermined intervals by spacers 19 embedded therein.

  The anode 7 and the cathode 8 are connected to an external DC power source. The liquid surface of the molten salt in the electrolytic cell is located between the upper part and the lower part of the curtain wall 5 by immersing most of the cathode 8 and the bipolar electrode in the molten salt. Further, although not shown so that the liquid level is constant, the metal accumulation chamber 3 is provided with a liquid level adjusting device so that the liquid level is controlled.

  By using such an electrolytic cell and energizing between the anode 7 and the cathode 8 by an external DC power source, a current flows from the anode 7 to the cathode 8 through the bipolar electrodes 12 and 13. With this current, chlorine gas is generated on the surface of the anode 7 and the bipolar electrodes 12 and 13 on the cathode 8 side, and Mg is generated on the surface of the cathode 8 and the bipolar electrodes 12 and 13 on the anode 7 side. Since the generated chlorine gas and Mg have a specific gravity smaller than that of the molten salt, an upward flow is generated between each of the anode 7 and the cathode 8 and the bipolar electrode, and the liquid level in the electrolytic chamber 2 rises.

  The raised chlorine gas is accumulated in the upper space of the electrolysis chamber 2, the pressure is adjusted, and the outside is taken out through the conduit 20. Further, Mg and molten salt that have risen in the electrolysis chamber 2 flow into the metal accumulation chamber 3 between the refractory wall 4 and the curtain wall 5 as indicated by an arrow B.

  Then, in the metal accumulation chamber 3, the inflowed Mg floats as shown by the arrow C due to the difference in specific gravity and accumulates at the upper part, and the molten salt flows as shown by the arrow D, and again passes through the lower part of the refractory wall 4. And flows into the electrolysis chamber 2 as indicated by an arrow E.

  Thus, in the electrolytic cell, the chlorine gas and Mg are separated by electrolysis, while the molten salt circulates through the electrolytic chamber 2 and the metal accumulation chamber 3.

  However, the sludge contained in the molten salt accumulates and accumulates between the electrode and the refractory during long-term use of the electrolytic cell, or the refractory is deteriorated or damaged in a molten salt or chlorine gas atmosphere at a high temperature and the sludge is removed. The sludge is circulated through the electrolytic chamber 2 and the metal accumulation chamber 3 together with the molten salt to wear the spacer 19 and the refractory pedestals 10, 11, 14 and 15. Furthermore, when the bipolar electrodes 12 and 13 and the anode 7 are worn due to bath convection of molten salt or reaction with MgO, and the wear increases, the bipolar electrode cannot maintain the predetermined interval between the electrodes as described above. Deviation may occur.

  When the position of the bipolar electrode is shifted and the predetermined distance between the electrodes cannot be maintained, the upward flow of chlorine gas, Mg, and molten salt is disturbed between the anode 7 and the cathode 8 and the respective electrodes of the bipolar electrode. The density of the current flowing between them gradually becomes nonuniform within each electrode surface. And current loss increases and current efficiency deteriorates.

  The current efficiency in the bipolar electrolytic cell has a current loss due to the above-described electrolysis stability. In addition to this current loss, current loss due to leakage of current through spacers and refractory pedestals that are in contact with each other between electrodes, or leakage of current through sludge accumulated on refractory pedestals (hereinafter referred to as “leakage current”). And a bypass current caused by leakage of current through the furnace wall refractory between a plurality of cathodes when using a bipolar multipolar electrolytic cell (hereinafter referred to as “bipolar electrolytic cell”). Can be categorized as loss.

  The above-mentioned current loss due to the stability of electrolysis is caused by, for example, deformation of the anode or cathode, or misalignment of the bipolar electrode, and loss due to leakage current or loss due to bypass current is used in the electrolytic cell. This depends on the refractory material to be used and the operating conditions of the electrolytic cell.

  In addition, when the above-mentioned double pole is displaced, the upward flow may be disturbed, and the flow may stay in the lower part of the double pole.In such a case, sludge accumulates, Metal Mg grains increase in the sludge, current loss is caused by current leaking through the sludge, and current efficiency is further deteriorated. In addition, when uneven wear occurs in the anode and the bipolar electrode due to turbulence in the upward flow, the efficiency is further deteriorated.

  For this reason, in electrolyzers that use a large amount of electric power, the power efficiency increases due to the deterioration of current efficiency, and the refractory pedestals and spacers that support the double pole and the double pole are worn or damaged. These improvements are required because the life of the electrolytic cell is shortened.

  In view of such a situation, in order to maintain the current efficiency in the bipolar electrode electrolytic cell, various proposals have been made regarding the shape of the bipolar electrode, the method of fixing the bipolar electrode, the structure of the electrolytic cell, and the like. For example, Patent Document 1 proposes a structure of an electrolytic cell in which a bowl-shaped groove is provided on the upper part of a bipolar electrode. In use, the rate of upward flow is increased, and the generated Mg can easily flow from the electrolytic chamber to the metal accumulation chamber. The chlorine gas and Mg generated between the anode, cathode and bipolar electrodes are not recombined in the upper part of the electrolysis chamber. However, productivity is improved by increasing the speed of the upward flow, but it is difficult to prevent recombination of chlorine gas and Mg at the upper part of the electrolysis chamber, and further through a bowl-shaped groove provided at the upper part of the double pole. In order to facilitate the flow of Mg into the metal accumulation chamber, the structure of the refractory wall between the electrolysis chamber and the metal accumulation chamber becomes complicated, the current efficiency cannot be improved, and the speed of the upward flow is increased to increase the bipolar and fire resistance. In some cases, the service life may be shortened due to increased wear of objects.

  Further, in Patent Document 2, in a bipolar electrolytic cell using bipolar electrodes (agreeing with bipolar), both ends of the refractory pedestal supporting the anode and the cathode and the lower part of the bipolar electrode are connected to the furnace wall, the electrolytic chamber and the metal. In order to fix to the shelf provided in the wall of the refractory material between the accumulation chambers, an electrolytic cell using an insulating block having a triangular cross section corresponding to the width of the shelf has been proposed. By adopting such a structure, molten salt stagnation is prevented in this shelf. In this way, the accumulation of sludge containing MgO as a main component and metallic Mg particles is prevented, and loss due to leakage currents generated between the anode, cathode and bipolar electrodes can be reduced. However, the wear of the bipolar electrode and the refractory cannot be suppressed, and the positional deviation of the bipolar electrode may occur, resulting in an increase in current loss due to the stability of electrolysis.

  Furthermore, in Patent Document 3, an electrolytic cell in which a part or all of the peripheral edge of an electrode including a bipolar electrode is covered with an insulator in order to reduce leakage current and prevent a decrease in current efficiency in the bipolar electrolytic cell. Has been proposed. In the proposed electrolytic cell, the electrode is made of titanium or the like as a substrate, and is an electrode containing a simple substance such as platinum, iridium or ruthenium or an oxide. The spacer used is a non-conductive resin. As a result, the current can be prevented from concentrating on the peripheral edge of the electrode. However, this bipolar electrolytic cell is an electrolytic cell for obtaining a highly corrosive hypochlorous acid solution as described as an example of use, such as 660 to 670 ° C. in a molten salt or chlorine gas atmosphere. It cannot be applied to the electrolysis of molten magnesium chloride used at high temperatures.

JP 59-6389

Japanese Patent No. 2772954 JP 2002-186970 A

  As described above, the conventional bipolar electrode cell cannot suppress the wear rate of the bipolar electrode and the refractory when used for a long period of time, and the deterioration of the current efficiency due to the positional deviation of the bipolar electrode cannot be avoided. May become shorter. In addition, even if a part or all of the peripheral edge of an electrode (including multiple electrodes) is covered with an insulator, the insulator to be covered should be a durable material when used under severe conditions. Equipment costs are significant.

  The present invention has been made in view of the above-mentioned problems, and when using an electrolytic cell for a long period of time, the refractory pedestal supporting the bipolar electrode or the bipolar electrode is worn by sludge circulating in the electrolytic cell together with the molten salt. Even so, it is an object of the present invention to provide a bipolar electrolytic cell capable of maintaining current efficiency without causing misalignment of the bipolar electrodes.

  In order to solve the above problems, the present inventor has made various studies on the conventional bipolar electrode electrolytic cell, and as a result, if the bipolar electrode does not shift from the refractory pedestal supporting the bipolar electrode, the spacer or It has been found that even if the refractory is somewhat worn, the predetermined interval between the electrodes can be maintained and the current efficiency can be maintained.

  The present invention has been completed on the basis of the above findings, and the gist thereof is the bipolar electrolytic cell of the following (1) and (2).

  (1) An electrolytic cell of molten magnesium chloride having a bipolar electrode, wherein the lower part of the bipolar electrode and the upper part of a refractory pedestal supporting the same are fitted together.

  (2) The bipolar electrolytic cell according to (1), wherein a concave groove is provided at a lower portion of the bipolar electrode, and a protruding protrusion is provided at an upper portion of the refractory base.

  The “fitting structure” defined in the present invention means that the lower part of the double pole and the upper part of the refractory pedestal that supports the double pole are provided with, for example, a concave groove on one side and a convex protrusion on the other side. This means that parts are provided and processed into a structure that can be fitted together with some play.

  According to the bipolar electrolytic cell of the present invention, the refractory pedestal supporting the bipolar electrode and the bipolar electrode is fitted with a structure so that even if the bipolar electrode or the refractory wears out over a long period of use, Since no pole misalignment occurs, current efficiency does not deteriorate and an increase in power cost can be suppressed. Furthermore, since the turbulence of the upward flow in the electrolysis chamber is reduced, the wear rate of the bipolar electrode and the refractory can be reduced, and the life of the electrolytic cell can be extended.

  As described above, the bipolar electrolytic cell of the present invention is characterized in that the lower part of the bipolar electrode and the upper part of the refractory pedestal that supports the bipolar electrode are fitted together, and the contents thereof will be described.

  FIG. 1 is a diagram showing an example of the structure of a bipolar electrolytic cell of the present invention. As described above, the bipolar electrolytic cell 1 is divided into the electrolytic chamber 2 and the metal accumulation chamber 3 by the refractory wall 4 and the curtain wall 5 and sealed by the lid 6.

  FIG. 2 is a front cross-sectional view of the structural example shown in FIG. 1 as viewed from the direction of arrows AA, and shows a state in which the double pole is held by a spacer. As shown in FIG. 2, the bipolar electrodes 12 and 13 are held at a predetermined interval by the anode 7 and a spacer 19 embedded in each of the bipolar electrodes. Moreover, the lower part of these and the upper part of the refractory bases 14 and 15 which support them are made into the fitting structure.

  FIG. 3 is a partial detailed cross-sectional view of the fitting structure indicated by the dotted line F in FIG. 2, and (a) shows an example of a fitting structure in which the bipolar or refractory pedestal has an uneven shape. , (B) shows an example of a dovetail-type fitting structure in which each of the bipolar or refractory pedestals has an uneven shape, and (c) both have concave grooves, and further refractory or An example of a fitting structure by sandwiching a ceramic rod or block is shown.

  FIG. 3A shows a structure in which the concave groove 21a of the bipolar electrode 13 and the convex protruding portion 22a of the refractory pedestal 15 are fitted together, and each has a structure of fitting with some play. The concave groove, the convex overhanging portion, and the play are selected according to the thickness of the bipolar electrode, and the height of the overhanging portion is preferably 3 mm or more. If it is less than 3 mm, the effect of preventing displacement is reduced.

  FIG. 3 (b) shows a structure in which the concave groove 21b of the bipolar electrode 13 and the convex overhanging portion 22b of the refractory base 15 are fitted more firmly. ing. By doing so, the bipolar electrode 13 does not move not only in the inter-electrode direction but also in the vertical direction, so that more stable electrolysis can be performed.

  3 (a) and 3 (b) have a structure in which the double pole has a concave groove and the refractory pedestal has a convex overhanging portion that is a “convex fit”. The projecting may be a “bottom convex fitting” in which a convex protrusion is provided on the pole and a concave groove is provided on the refractory base. In this case, “upward convex fitting” is more desirable as a fitting structure than “lower convex fitting”. The reason is that the protruding portion of the refractory pedestal in the “upwardly convex fitting” is surrounded by a multipolar groove with high electrical conductivity. This is because the potential difference is reduced and the action of electrolytic corrosion is reduced. In addition, the structure of the “convex fitting downward” is likely to cause leakage current because sludge easily accumulates between the bipolar electrode and the refractory pedestal, and therefore the refractory pedestal is more likely to cause electrolytic corrosion. .

  Further, FIG. 3C shows that a concave groove 23 is provided in both the bipolar electrode 13 and the refractory pedestal 15, and a refractory or ceramic rod or block 24 is formed in the space where the concave grooves 23 are overlapped. The structure is sandwiched with some play. In this case, the size and play of the concave groove 23 are selected according to the thickness of the bipolar electrode as described above, and it is desirable that the depth of the groove is 3 mm or more.

  Furthermore, it is desirable that the concave groove and the projecting protruding portion extend over the entire length of the width of the bipolar electrode, but it is also possible to adopt a structure in which the bipolar electrode or the refractory pedestal is partly fitted.

  1 and 2 exemplify an anode and a cathode and two bipolar electrodes as electrodes, but in order to improve the productivity of separation and recovery of Mg when installing a bipolar electrolytic cell. Further, a bipolar electrolytic cell in which the number of bipolar electrodes is further increased or a plurality of combinations of anodes, cathodes, and bipolar electrodes are provided in one electrolytic cell can be provided.

  In the above, the anode, the cathode, and the bipolar electrode are illustrated as plate-like. However, in the case where the cylinder and the cylindrical electrode are arranged concentrically, the bipolar electrode and the refractory base are similarly formed. A fitting structure can be applied.

  In order to confirm the effect of the present invention, the molten salt was electrolyzed using a bipolar electrolytic cell having a fitting structure as shown in FIGS. 1, 2, and 3 (a).

  The method of evaluating the effect of the present invention is that the average current efficiency and the life of the electrolytic cell in a conventional multi-electrode electrolytic cell having a conventional planar structure in which the lower part of the bipolar electrode and the upper part of the refractory pedestal are not fitted are 100 Those in the present invention are compared in terms of relative ratios (%) that make the current efficiency ratio and life ratio. The life of the electrolytic cell is the length of the period until the current efficiency during operation decreases to a predetermined current efficiency. The average current efficiency is the average of the current efficiency from the start of operation of the electrolytic cell until it stops at the end of its life.

  Table 1 shows the relative ratio (%) between the current efficiency and the life of the electrolytic cell for the above-described conventional planar structure and “upward convex fitting” and “downward convex fitting”. It can be seen that the fitting structure of the present invention improves both the current efficiency and the life of the electrolytic cell as compared with the conventional planar structure.

  Further, if the spacer is made of silicon nitride ceramics, the wear and damage of the spacer are reduced and the loss due to the leakage current is reduced, so that the current efficiency and the life of the electrolytic cell are further improved.

  According to the bipolar electrolytic cell of the present invention, even if the bipolar electrode or the refractory is worn during a long-term operation, there is no misalignment of the bipolar electrode, and the predetermined interval between the electrodes is maintained and the electrolysis is stabilized. Since the current efficiency does not deteriorate, an increase in power cost can be suppressed. Furthermore, since the turbulence of the upward flow during electrolysis is reduced, the wear rate of bipolar electrodes and refractories can be suppressed, and the life of the electrolytic cell can be extended, so it is widely adopted as a bipolar salt electrolytic cell for molten salt. .

It is a figure which shows the structural example of the bipolar electrolytic cell of this invention. It is front sectional drawing by the AA arrow of the structural example shown in the said FIG. FIG. 3 is a partial detailed cross-sectional view of the fitting structure indicated by the dotted line F in FIG. 2, and (a) shows an example of a fitting structure in which the bipolar or refractory pedestal has an uneven shape. , (B) shows an example of a dovetail-type fitting structure in which each of the bipolar or refractory pedestals has an uneven shape, and (c) both have concave grooves, and further refractory or An example of a fitting structure by sandwiching a ceramic rod or block is shown.

Explanation of symbols

1: Bipolar electrolytic cell, 2: Electrolytic chamber, 3: Metal accumulation chamber, 4: Refractory wall 5: Curtain wall, 6: Lid, 7: Anode, 8: Cathode, 9: Furnace wall 10, 11: Refractory pedestal, 12, 13: Bipolar, 14, 15: Refractory pedestal 16, 17: Shelf, 18: Insulating block, 19: Spacer 20: Conduit, 21a, 21b: Concave groove, 22a, 22b: Tension Protruding portion 23: concave groove, 24: refractory or ceramic rod or block

Claims (2)

  An electrolytic cell of molten magnesium chloride having a bipolar electrode, wherein a lower part of the bipolar electrode and an upper part of a refractory pedestal supporting the same are fitted together. 2. The bipolar electrolytic cell according to claim 1, wherein a concave groove is provided at a lower portion of the bipolar electrode, and a protruding protrusion is provided at an upper portion of the refractory base.

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