US1921376A - Apparatus for electrolysis of fused bath - Google Patents

Description

Aug. 8, 1933. L. E. WARD APPARATUS FOR ELECTROLYSIS FUSED BATH s Sheets-Sheet 1 Filed 001;. 5, 1951 \di l l INVENTOR BY ATTORNEY Aug. 8, 1933. E. WARD APPARATUS FOR ELECTROLYSIS OF FUSED BATH Filed Oct. 5, 1931 3 Sheets-Sheet 5 INVENTOR A'ITORNEY Patented Aug. 8, 1933 UNITED STATES APPARATUS FOR ELIACT'IIIROLYSIS 0F FUSED Louis E. Ward, Midland, Mich assignor to The Dow Chemical Company, Midland, Mich., a Corporation of Michigan Application October 5, 1931. Serial No. 566,836

11 Claims.

The invention relates to apparatus for electrolyzing a fused salt bath to produce a metal lighter than the electrolyte, more particularly a bath containing magnesium chloride to produce magnesium.

The products of such electrolysis, e. g. magnesium and chlorine, both rise to the surface of the bath and must be separately collected and removed so as to prevent recombination thereof. It has been the usual practice to provide an electrolytic apparatus consisting essentially of an iron or steel vessel to contain the electrolyte and to act as cathode, one or more graphitized carbon anodes depending in the bath in the vessel, and a non-conducting partition of refractory material dipping into the'bath between the anode and cathode surfaces to separate the anode and cathode products at the surface of the bath. This simple form of structure has certain inherent defects which give rise to operating difliculties and also unduly increase the power consumption per unit of product. The-refractory partitions are fragile and subject to frequent breakage, necessitating replacement thereof which interrupts regular operation of the cell. This is especially a serious problem in the larger sizes of cells. Various designs of composite or sectional partitions have been described and actually used, none of which, however, have entirely overcome the fundamental defects of thisstructural element.

Another disadvantage of the aforesaid cell structure, in which the vessel itself is the cathode, is that the electrode surfaces are of necessity spaced relatively far apart in order to provide for separately taking off the products of the electrolysis at the surface of the bath. It is desirable to bring the electrode surfaces closer together in order to shorten the current path through the bath, thereby reducing the electrical resistance of the cell and consequently the power consumption per unit of product. Various proposals have been made for accomplishing this result by inserting a supplemental cathode in the cell between the walls of the vessel and the anode or anodes, but in all such of which I am aware the result has been simply to reduce the available surface area between the active electrodes for separating anode and cathode products and thus to magnify the difiiculty of-efiecting a practicable segregation without excessive losses through recombination.

It is an object of the present invention to provide a novel form of cathode which, when incorporated in a cell structure of the type hand, enables the rapid removal from the active zone of the light metal as it is formed on the cathode surface, such removal being accomplished to a great extent before the metal rises to the surface of the bath. The metal thus removed is collected by suitable means in the inactive zone between the cathode and the walls of the vessel where it may be kept out of contact with the gaseous anode products without necessity for providing any separating partition bewithout loss of current efliciency due to inter mixing and recombinationof anode and cathode products, thereby reducing the electrical resistance of the cell and increasing its energy eificiency. The invention is set forth in the accompanying drawings and following detailed de-' scription illustrating various forms of structure embodying the principle of the invention.

In the drawings:--

Fig. 1 is a. representation in cross section of a cell structure embodying one form of my im- .proved cathode. Figs. 2-4 illustrate in similar I fashion alternative forms of cathode. Fig. 5 is a longitudinal section showing part of a cell structure containing a plurality of anodes and also showing means for collecting the metal product of the electrolysis.

As will appear directly from the drawings, the cathode is composed of a series of horizontal members, such as slats or bars or the equivalent, disposed in proximity to the anode surface, the broad face of the bars being inclined upwardly away from the anode, one bar above the other in spaced relation substantially in the form of a louver. For brevity this form of cathode structure will hereinafter be designated as a louver type cathode.

Referring to the drawings, in Fig. l is shown a pot or vessel 1 of iron or steel to contain the fused salt bath, such vessel being suspended in a brickwork setting 2 or the equivalent enclosing a chamber 3 which constitutes a heat-insulating air bath surrounding the vessel. The edge of vessel 1 is provided with an external flange 4, preferably having an L-section, which is supported on a bearing plate 5 set in the brickwork. Projecting inwardly from the upper edge of vessel 1 is a downwardly directed trough-like flange 6 forming aninverted trough or trap '7 for gathering the metal product of the electrolysis. A thick course of heat-insulating material 8, such as fire brick or thelike, is supported and held in place by flanges 4 and 6, leaving a central chamber 9 into which depends one or more vertically adjustable anodes 10 of graphitized carbon. Chamher 9 is provided with a cover 11, through which is inserted an outlet connection 12 for carrying away the chlorine produced by the electrolysis.

A lug 13 on the rim of flange 4 serves for attaching a negative electrical connection to a source of direct current, while the positive connection may be made to the anodes in any known manner.

The louver type cathode may consist of a vertically spaced bank of horizontal bars or slats 14 on either side of anode 10, bars 14 being inclined away from the anode at an angle preferably of about 45. The bars may be attached to the walls of the pot in any suitable way for support and to make electrical contact therewith. Here they are shown supported upon ribs 15 of vessel 1, being preferably welded thereto. Ribs 15 may be cast integrally with the pot or welded thereto. Bars 14 are so positioned with respect to flange 6 that the front edge facing the anode is advanced closer thereto than is the flange, while the rear edge of the bars preferably aligns slightly back of the inner rim of the flange.

In operating the cell, the vessel 1 is filled with a molten salt bath containing magnesium chloride to a level approximately as shown to submerge trough '7 completely, heat being supplied to chamber 3 by any suitable means, not shown, in order to maintain the bath in a freely fluid condition, and the current turned on. The active cathode surfaces consist substantially of the front edge and upper and lower faces of bars 14, and on these surfaces magnesium forms as the electrolysis proceeds. .The temperature of the bath is maintained above the melting point of magnesium by the thermal effect of the electric current passing therethrough supplemented, if need be, by external heat supplied to chamber 3. The metal formed collects in droplets or globules on the cathode surface, which increase in size until they break loose and float upwardly through the bath.

By the use of a louver type cathode, as herein described, the metallic globules in rising are deflected by the bars immediately above and caused to rise into the space back of the cathode where they are caught and accumulated in the trough '7. The flow of the metallic globules in the desired direction is also aided by the movement of the bath away from the anode caused by displacement thereof by chlorine gas evolved .at the anode surface. I'he metal accumulating in trough '7 is forced through a suitable port by the hydrostatic head of the bath at the level in chamber 9 into a collecting well 16 at one side or end of the cell as shown in Fig. 5 and more particularly described hereinafter.

The louver form of cathode herein described may be located closer to the anode than any type of cathode opposing a continuous surface thereto, while permitting .the" metal formed to be withdrawn and segregated from the anode Leanevc ually wears down by erosion or chemical action to a shape roughly indicated by the dotted lines in Fig. 1'. The necking down effect at the upper part of the active anode surface appears to be more or less characteristic under the conditions. This is a disadvantage as the anode is liable to break off eventually at the neck. I have found, however, that the use of a tapered form of cathode, in which the sides gradually converge downwardly toward the anode as shown in Fig. 2, counteracts materially the tendency to neck down, so that the anode wears down more nearly with a uniform taper. The inverted tapered form of cathode is constructed by setting back slightly the leading edge of each bar from a vertical line with the edge of the next lower member. It has the further advantage that the lower part of the cathode may be brought closer to the anode than is practical with a vertical cathode without interfering with the effective separation of anode and cathode products.

In Fig. 3 an alternative arrangement is shown partly in section and partly in elevation, consisting in a continuous bar or strap wound in a tapered spiral in the form of an inverted truncated cone which surrounds the anode. The flat face of the strap is set at a suitable inclination to the anode, and the pitch is preferably such that the upper edge of each turn of the spiral is level with, or slightly overlaps, the lower edge of the next turn above it. With such a cathode is also shown a modification of accessory cell details, whereby spiral member 17 is welded to a collar 18 so as to be suspended therefrom, and collar 18 in turn is welded to a flat bearing ring 19, which rests upon a flat inner flange 20 at the rim of the vessel 1. Flange 20 and collar 18 together form an inverted trough corresponding to the one illustrated in Figs. 1-2. a

Fig. 4 shows still another arrangement in which the inverted metal collecting trough and the louver type cathode are constructed integrally in one piece, which is supported upon the rim or shoulder of vessel 1. In Figs. 3 and 4 the cathode connection 13 may be attached directly to the cathode structure, as shown, instead of to the vessel 1.

Fig. 5 shows in partial longitudinal section an electrode arrangement similar to that illustrated in Figs. 1 and 2 adapted to a cell structure employing a plurality of anodes in a row.

In addition to the longitudinal members 14 crossmembers 14a are provided at the end and between adjacent anodes 10, thereby presenting an active cathode surface which completely circumscribes each anode. Conveniently, cross-members 14a may consist of a number of flat iron or steel plates or bars set edgewise and spaced apart vertically one above the other, and welded at the ends to the members 14. Just above each cross-member is an inverted trough for trapping globules of metal which rise from the active cathode surface therebelow. Troughs 21 are open at the ends, so that the metal trapped therein flows out at the ends into the space between member 14 and the vessel wall, wherein it rises into trough '7. Troughs 21 may be conveniently supported by welding to the bottom of cross-members 14a, as in the manner shown. At either end of the row of anodes the cross-members 14a. may be provided simply with inclined plates 22 to deflect away the globules of metal rising from below so that they can rise into collecting trough '7.

An extension of vessel 1 is provided at one end to form a collecting well 16 for molten metal already referred to, into which the metal is conducted from the inverted trough 7. The trough 7 is carried entirely around the row of anodes so as to form the perimeter of a rectangle the sides of which are approximately uniformly spaced from the anodes. At the end of the cell forming the collecting well 16, trough '7 bridges across between the side walls of the vessel. A port 23,

shown by the dotted lines, is provided in the bridge section of trough 7 cormnunicating with collecting well 16. The hydrostatic pressure of Other modes of applying the principle of the.

invention may be employed instead of those explained, change being made as regards the structure herein disclosed, provided the means stated by any of the following claims, or the equivalent thereof, be employed.

I therefore particularly point out and distinctly claim as my invention:--

1. In an electrolytic apparatus for producing a metal lighter than the electrolyte, the combination of a vessel to contain a molten salt bath constituting the electrolyte, one or more anodes depending in such bath, a louver type cathode with inclined surfaces sloping upwardly away from the ano'de and means to collect molten metal rising through the bathfrom said cathode.

2. In an electrolytic apparatus for producing a metal lighter than the electrolyte, the combina-' tion of a' vessel to contain a molten salt bath constituting the electrolyte, one or more anodes depending in such bath, a louver type cathode with inclined surfaces sloping away from the anodes; an inverted trough-like structure submerged below the level of the bath and adapted to intercept molten metal rising through the bath from said cathode,'and a metal collecting wellcommunicatingwith said inverted trough.

3.'In an electrolytic apparatus for producing a metal lighter than the electrolyte, the combination of a vessel to contain a molten salt bath constituting the electrolyte, one or more anodes depending in such bath, a lofuver type cathode o'pposed to and downwardly converging toward the anode, said cathode having inclined surfaces sloping away from the anode; an inverted troughlike structure submerged below the level of the bath and adapted to intercept molten metal rising through the bath from said cathode, and a cumscribing each anode individually .and having inclined surfaces sloping upwardly away from the anode; an inverted trough-like structure substituting the electrolyte, a plurality of anodes depending in such bath, a downwardly converging louver type cathode circumscribing each anode individually and having inclined surfaces sloping upwardly away from the anode; an inverted trough-like structure submerged below the level of the bath and adapted to intercept molten metal rising through the bath from said cathode, and a metal collecting well communicating with said inverted trough.

6. In an apparatus for electrolyzing a fused salt bath to produce a metal lighter than the electrolyte, a cathode in the form of a louver composed of generally horizontal members spaced one above the other the broad surfaces of which are inclined upwardly and outwardly with respect to the enclosing walls of the apparatus, each member being set back slightly from a vertical line with the leading edge of the next lower member. n

7. Inan apparatus for electrolyzing a fused salt bath to produce a metal lighter than the electrolyte, a cathode in the form of a louver composed of a continuous spirally wound flat bar, the fiat face of which is inclined upwardly and outwardly from the center.

8. In an apparatus for electrolyzing a fused salt bath to produce a metal lighter than the electrolyte, a cathode in the form of a flat barwound in a downwardly tapering spiral to form an inverted truncated cone, the flat face of the bar being inclined upwardly and outwardly from the center.

9. In an apparatus for electrolyzing a fused bath containing magnesium chloride to produce magnesium, the combination of one 'or more vertical anodes of graphitized carbon depending in such bath and a cathode opposed thereto in spaced relation, said cathode being in the form of a louver composed of horizontal bars of iron or steel spaced one above the other, the broad surfaces of which bars are inclined upwardly away from the anode.

being in the form of a louver composed of iron or steel bars spaced one above the other, the broad surfaces of which bars are inclined upwardly away from the anode.

11. In an apparatus for electrolyzing a,fused bath containing magnesium chloride to produce magnesium, the combination of oneor more vertical anodes of graphitized carbon depending in such bath and a cathode individually circumscribing each anode, such cathode being in the form of a louver composed of a continuous spirally wound iron or, steel bar, the flat face of which is inclined upwardly away from the anode.

LOUIS E. WARD.

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