US2879213A - Electrolytic method and apparatus - Google Patents

Description

March 24, 1959 F. A. HOWARD 2,879,213 ELECTROLYTIC METHOD AND APPARATUS Filed Oct. 22, 1956 Fig.5

INVENTOR. Frank ApHoward BY Fig.2

ATTORNEY U i S te P m i 2,879,213 ELECTROLYTIC METHOD AND APPARATUS Frank A. Howard, New York, N.Y. Application October 22, 1956, Serial No. 617,338 2 Claims. (Cl. 204-64) This invention relates to the production of metals involving the electrolysis of a fused salt bath. More particularly, it relates to a method and'to an apparatus for carrying out the electrolysis in a cell constructed and designed so that the electrolyte or the fused melt has virtually no free surface, that is, one in which the surface of bath as well as the cell surface exposed to any gaseous phase is negligible.

In recent years interest has revived in the recovery of the rare and refractory metals of groups IV-A and V-A of the periodic table by electrolytic procedures involving the use of molten inorganic salts at relatively high temperatures. Aluminum and other metals havefor many years been recovered inthis manner. The presence of a large free surface of the-electrolyte and acorresponding large cell surface "ex'posedkto vapors has created a number of problems in the operation of the electrolytic cell and various expedients have been proposed to overcome the undesirable phenomena associated with these conditions. Thus, in many instances, means are provided for minimizing the condensation of vapor on surfaces within the uppermost portions of the cell. In other instances costly gases, such as helium, constantly flow through the cell to create aninert atmosphere above the free surface and to purge the cell of any reaction products in vapor form as rapidly as they are formed in order to avoid corrosive or chemical attack on the materials of which the cell is constructed, as well as undesirable side reactions. Furthermore, at the high temperatures generally encountered in fused salt electrolyses, the escape of the more volatile constituents from the salt melt results in many instances in substantial changes in the composition of the melt and requires continuous adjustment to compensate for the changes in bath composition.

I have now discovered a simple an inexpensive manner whereby the disadvantages accompanying the prior art processes for winning metals by electrolysis of molten salt baths may be avoided and a uniformity and continuity of operation hitherto unobtainable are made possible. In brief, in accordance with my invention, the electrolysis is carried out in a cell designed to provide no free surface of electrolyte, the vapor disengaging area being minute and restricted to a passage through which excess electrolyte may be drawn off. As a result, no special means are required to heat the uppermost regions of the cell to a temperature sufficient to avoid condensation of vapors on the inner surfaces of a vapor space within the cell. Furthermore, the absence of any accumulation of condensed fume avoids the necessity of taking the cell out of production for purposes of removing such condensates from time to time. Still another benefit which is obtained lies in the fact that the possibility of side reactions is eliminated by doing away with a free space in which volatile products can collect and accumulate. My invention will be more fully understood by reference to the accompanying drawings, in which 2,879,213 Y. ete M 45 2 several ways of accomplishing the desired result are shown.

. In the drawings: Figure 1 is a diagrammatic representation of one cell construction according to my invention, seen in section; Figure 2 shows a somewhat modified cover arrangement;

Figure 3 illustrates a further modification in the cover; and

Figure 4 is a diagrammatic showing of one form of re- 7 moving gases from the system.

R eferring now to the figures, it will be seen that the cell in Figure 1 comprises a container 10 provided with inlet 12 to admit electrolyte into the cell near the bottom of the cell and with means 14 providing a passage through which electrolyte may be continuously or intermittently removed from the top of the cell. All volatile material which would tend to accumulate is trapped out in a small trap (not shown) in outlet passage 14 and is withdrawn through a vertical riser 16. One suitable trap construction is shown in Figure 4. The cell is provided with a cover 18.' Suitable heating means,not shown, are provided for maintaining the contents of the cell and the contents of all associated conduits and vessels at any desired elevated temperatures and such means, which are conventional in the art, form no part of the present invention. In the cell shown, the crucible 10 is provided with an anodic lining'24. One or more cathode rods 26 are suspended through the cover 18 and into the melt. Means for raising and lowering the cathode are schematically shown as a rack 20 and pinion 22. Means are provided for removing the cathode deposit without interrupting the continuity of operation of the cell. A gate valve 30 slides across the neck of the cell when cathode rod 26 is raised against a knife edge on the cover 18 whereby the deposit is severed from the rod 26 and permitted to slide down the valve plate 30 through chute 38 into a collection hopper 38' filled with a molten salt. A separately operated scraperhoe 34 may be used to push the deposit along plate 30 past a counterweighted door 36 separating the discharge chute from the cell. A conduit 40 delivers molten salt to the hopper 38' and carries off the molten salt and cathode deposit. Electrolyte leaving the cell passes from outlet 14 to .a regenerator (not shown), by means of a conduit into which the outlet 14 leads. The cathode deposit is shown in dotted lines as 42 and the knife means for severing it from the cathode supporting rod 26 is shown at 44. It may also be advantageous to provide a mechanical stirrer or agitator (not shown) to insure that any vapor formed on the surface of the anode 24 may be detached therefrom as it forms.

In Figure 2, a section at right angles to Figure 1, the inclination of cover 18 is greatly exaggerated for purposes of illustration, and the primed reference numerals correspond to the similar elements in Figure 1.

In Figure 3 there is diagrammatically shown a detail of a modified cathode withdrawal chamber which differs from that shown in Figure 1 principally in the shape of the cathode rod on which the cathode deposit is collected. As shown, the rod comprises an enlarged upper portion 26 and a smaller lower portion on which the deposit forms. The enlarged portion 26" substantially fills a cap 46" in the cover 18 so that no free vapor space exists in the cathode withdrawal chamber when the cathode is in its uppermost position. In this instance severing means 44" are retractable about cathode rod 26" and move into engagement with the deposit while the enlarged portion of the rod enters cap-shaped chamber,

cells arranged in the manner common in the refining of aluminum and served with a common supply of molten electrolyte to the inlet 12 and with a common electrolyte withdrawal header into which outlet 14 opens. Furthermore, the electrolyte may be either continuously or intermittently admitted to and evacuated from the cells. Each cell has a separate electrolyte drain in the bottom (not shown).

When operating with cells constructed as above de scribed, the electrolyses proceed in an orderly manner at voltages and current densities not materially different from those required heretofore in the art. However, the operation of the cell is more uniform and less subject to interruptions and to the harmful effect of side reactions. For instance, when carrying out the production of titanium by the electrolysis of a fused salt-containing fluoride as described in United States Patent 2,731,402, the corrosive reaction of alkali metal-fluorine compounds condensing in the inner surface of the electrolytic cell is entirely avoided by the practice of my invention and as a result, the bath composition is much more readily maintained uniform than was heretofore possible. Also the amount of inert gas such as argon introduced into the cell to maintain an inert atmosphere in contact with the liquid surface is greatly reduced and could .even be eliminated when the electrolysis is conducted with substantially no free surface of electrolyte in accordance with my invention.

Having now described my invention in accordance with the patent statutes, I claim:

1. In an electrolytic cell comprising: a container adapted to confine within its inner surfaces a molten salt bath; a

cover for said container, an anode and a cathode in elec trical contact with one another only through the electro lyte; means for passing an electrolyzing current between said anode and said cathode; inlet means for admitting electrolyte into said container and outlet means for voiding liquid from the most elevated portion of said cell,.

dand therefore for maintaining said container substantially completely filled with molten salt whereby no free vapor can accumulate within the confines of said covered container and a gas trap in the outlet means, positioned at least as elevated as the inner surface of the cover of said cell, said trap providing a vapor disengaging surface which is minute in area relative to the cross sectional area of the main body of electrolyte in said cell.

2. A method of electrolyzing a fused salt bath in the absence of a substantial volume of accumulated vapor in physical contact with the uppermost inner surfaces of the cell in which the fused salt is being electrolyzed; characterized by the following improvements: providing an electrolytic cell, vessel adapted to contain a fused salt electrolyte, having a cover for the uppermost portion of the vessel, and electrolyte inlet for admitting electrolyte into said vessel and an electrolyte outlet for discharging electrolyte from said uppermost region; maintaining a sufficient volume of molten salt in the electrolytic cell vessel to completely fill the cell vessel and the outlet, with molten salt; and sufficient to maintain the uppermost level of the molten salt in physical contact with the inner surface of the cover; and diminishing the surface area of electrolyte in contact with a free space into which gas may pass from said electrolyte, by providing as the vapor disengaging surface, an area located in the outlet passage and at least as elevated as the uppermost region in the cell, said area being minute as compared with the cross sectional area of the main body of electrolyte in said cell.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0. 2,879,213 Y March 24, 1959 Frank A. Howard It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 14, after "cell" strike out the comma; line 16, for 14 "and electrolyte" read and an electrolyte Signed and sealed this 7th day of July 1959.

(SEAL) Attest:

KARL H. AXLINE 7 ROBERT C. WATSON Commissioner of Patents Attesting Officer

Claims (2)

1. IN AN ELECTROYLTIC CELL COMPRISING: A CONTAINER ADAPTED TO CONFINE WITHIN ITS INNER SURFACES A MOLTEN SALT BATH; A COVER FOR SAID CONTAINER, AN ANODE AND A CATHODE IS ELECTRICAL CONTACT WITH ONE ANOTHER ONLY THROUGH THE ELECTROLYTE; MEANS FOR PASSING AN ELECTROLYZING CURRENT BETWEEN SAID ANODE AND SAID CATHODE; INLET MEANS FOR ADMITTING ELECTROLYTE INTO SAID CONTAINER AND OUTLET MEANS FOR VOIDING LIQUID FROM THE MOST ELEVATED PORTION OF SAID CELL, SAID INLET MEANS AND OUTLET MEANS TOGETHER CONSTITUTING MEANS FOR MAINTAINING THE VOLUME OF ELECTROLYTE IN SAID CELL SUFFICIENT FOR THE UPPER LEVEL OF LIQUID ELECTROYLTE TO BE IN PHYSICAL CONTACT WITH THE INNER SURFACE OF THE COVER AND THEREFOR FOR MAINTAINING SAID CONTAINER SUBSTANTIALLY COMPLETELY FILLED WITH MOLTEN SALT WHEREBY NO FREE VAPOR CAN ACCUMULATE WITHIN THE CONFINES OF SAID COVERED CONTAINER AND A GAS TRAP PROVIDING A VAPOR DISENGAGING SURFACE AT LEAST AS ELEVAED AS THE INNER SURFACE OF THE COVER OF SAID CELL, SAID TRAP PROVIDING A VAPOR DISENGAGING SURFACE WHICH MINUTE IN AREA RELATIVE TO THE CROSS SECTIONAL AREA OF THE MAIN BODY OF ELECTROYLTE IN SAID CELL

2. A METHOD OF ELECTROLYZING A FUSED SALT BATH IN THE ABSENCE OF A SUBSTANTIAL VOLUME OF ACCUMULATED VAPOR IN PHYSICAL CONTACT WITH THE UPPERMOST INNER SURFACES OF THE CELL IN WHICH THE FUSED SALT IS BEING ELECTROLYZED; CHARACTERIZED BY THE FOLLOWING IMPROVEMENTS: PROVIDING AN ELECTROYLTIC CELL, VESSEL ADAPTED TO CONTAIN A FUSED SALT ELECTROLYTE, HAVING A COVER FOR THE UPPERMOST PORTION OF THE VESSEL, AND ELECTROLYTE INLET FOR ADMITTING ELECTROLYTE INTO SAID VESSEL AND AN ELECTROLYTE OUTLET FOR DISCHARGING ELECTROLYTE FROM SAID UPPERMOST REGION; MAINTAINING A SUFFICIENT VOLUME OF MOLTEN SALT IN THE ELECTROLYTIC CELL VESSEL TO COMPLETELY FILL THE CELL VESSEL AND THE OUTLET, WITH MOLTEN SALT; AND SUFFICIENT TO MAINTAIN THE UPPERMOST LEVEL OF THE MOLTEN SALT IN PHYSICAL CONTACT WITH THE INNER SURFACE OF THE COVER; AND DIMINISHING THE SURFACE AREA OF ELECTROLYTE IN CONTACT WITH A FREE SPACE INTO WHICH GAS MAY PASS FROM SAID ELECTROLYTE, BY PROVIDING AS THE VAPR DISENGAGING SURFACE, AN AREA LOCATED IN THE OUTLET PASSAGE AND AT LEAST AS ELEVATED AS THE UPPERMOST REGION IN THE CELL, SAID AREA BEING MINUTE AS COMPARED WITH THE CROSS SECTIONAL AREA OF THE MAIN BODY OF ELECTROLYTE IN SAID CELL.

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