US2194444A - Fused salt electrolysis cell - Google Patents

Description

March 19, 1940. R. E. HULSE Er AL FUSED SALT. ELECTROLYSIS CELL Filed July 6, 1937 2 Sheets-Sheet l 'ROBE LTRS VIR G11. HA AISLE@ BY HRMA/v (LLA UGHL/N IN RT E.

ATTORNEY.

March 19, 1940. R. E. HuLsE r-:r Al.

FUSED SALT ELECTROLYSIS CELL Filed July 6. 193'? 2 Sheets-Sheet 2 INVENTOR VIOBET HgLS lil estema Mu. 19, 1940 UNITED STATES gara Falls', and Herman G. Laughlin, Tonawanda, N. Y., assignors to E. I. du Pont de Wilmington Nemours Company, poration of Delaware Del., a oor- Appuesuon my s. 1931, ser-Isl No. 152,246

1o claim. (ol. :o4-10) This invention relates to an improvement in fused salt electrolysis cells, for example, cells used to electrolyze light metal halides to produce halogen and the corresponding metal.

In the operation of fused salt electrolysis cells,

in the electrolysis of substances which evolve gaseous products at one or both electrodes,.difll culty is ordinarily experienced because of more or less violent splashing of the molten salt electrolyt'e at the point where evolved gas leaves the electrolyte. In a large installation in which a high rate of production is obtained, the rapid evolution of gas causes a violent surface agitation of the electrolyte just below the point where the gas is collected. The resultant splashing of the electrolyte causes portions of the liquid to come into contact with the cooler upper surfaces of the gascollecting device or into the gas leadci! pipe. Most of the liquid so splashed up tends to solidify on such cooler surfaces and consequently it is necessary frequently to .open the collecting device or gas lead-off pipe and clean out the solidied electrolyte.- Sometimes this entails shutting down the electrolysis, which, is troublesome and expensive and even when it is not necessary to stop the electrolysis operation, opening the collecting device or pipes to clean out the frozen salt causes dilution of the gas with air, thereby resulting in amore impure gaseous product and escapeof the gas, which is wasteful and often hazardous to the operator.

An object of the. p'resent invention is to prevent the splashing of electrolyte in fused salt electrolysis cells in which gaseous products are obtained. A further object is to prevent the incnistation of gas collecting devices with -frozen electrolyte in fused salt electrolysis cells. Another object is to provide an improved apparatus for fused salt electrolysis for the production of gaseous products. Other objects of this invention will be apparent from the following description thereof.

'Ihe above objects may be attained in accordance with the present invention by providing in a fused salt electrolysis cell a means for rapidly circulating the electrolyte in the region where gaseous products are evolved so that, at the point where gas leaves the electrolyte, the ,latter flows in a relatively rapid stream. More speciilcally, we cause the liquid electrolyte to rise together with the gaseous electrolysis product towards the surface where the gas escapes from the liquid, cause a rapid liquid flow at that point in such manner asfto avoid splashing and then ilow substantially gas-free liquid downwardly from the point where the gas escapes. In the practice of our invention, we preferably achieve this effect by taking advantage of the "gas-lift" effect of the ascending gas liberated from an electrode which tends to cause an upward ilow of the electrolyte toward'the point where the gas is discharged from the cell. To utilize this gas-lift effect, we insert in the cell suitable bailles, a down-flow tube or tubes or equivalent means so that the electrolyte lying above the point of ygas formation is caused to rise by the gas-lift effect of the ascending gas bubbles and then, near the point where the gas is discharged from the'cell, the liquid is caused to ow downward, for example, through one or more suitable down-flow tubes, through a region where gas evolution does not occur.

To illustrate our invention we shall describe its adaptation to a well-known type of fused salt electrolysis cell, hereinafter referred to as the Downs cell, which is described and claimed in U. S. P. 1,501,756. 'I'he Downs cell as shown in the. aforesaid patent has a centrally located graphite anode surrounded by an annular steel cathode and is ordinarily used for the electrolysis of' fused alkali metal halides to produce alkali metal and halogen, gas, for example, to produce sodium and chlorine. Above the annular cathode is suspended a circular trough for collecting the metal liberated at the cathode while a coneshaped hood, surmounted by a cylindrical dome, is utilized to collect the gaseous product formed at the anode. In the normal operation of the Downs cell, the rapid evolution of halogen gas causes considerable splashing of the molten electrolyte in the dome at the top of the gas collector, which electrolyte tends to freeze on the relatively cooler walls of said dome. To prevent blocking the off-gas pipe leading from the dome, it is necessary to remove frozen salt from the dome at frequent intervals.

In adapting our invention to the Downs cell, we may insert therein a down-draft tube as illustrated by the drawings or equivalent means to cause rapid circulation of the electrolyte from the anode region towards the point of gas discharge and thence back down into the cell. Fig.

suitable refractory material, a centrally located` anode 2 made of graphite, an annular cathode surrounding said anode, a cylindrical diaphragm 4 made of wire gauze and suspended between the anode and cathode, inverted collecting trough I; suspended above the cathode to collect rising a1- kali metal, .and a conical gas collecting hood O surmounted by the gas collecting dome 1. 'I'he gas collecting hood 6 may be constructed of steel since it is entirely submerged in the fused salt and is thereby protected from the action of the halogen gas. Gas collecting dome 1 may be made of ,suitable ceramic material. to withstand the action of the halogen gas above the surface oi' the electrolyte. Lead-off pipe 8 is connected to the iop of dome 1 to carry of! the halogen gasl as produced. 'I'he alkali metal collector I is provided with a pipe 0 through which molten alkali metal rises and is led into the receiver Il. 'I'he cell is provided with a cover II in which there is an opening Il for feeding salt into the cell. 'Ihe cover II may be omitted, if desired. Suspended within the gas collecting hood 6 and extending into the dome 1 is a down-now pipe Il. The upper portion of pipe II is surmounted by graphite tube Il, near the upper end of which` is a plurality of vertical, radial slots 2| extending through the walls of the graphite tube and extending vertically from a point near the end of the tube down to a point near the main level of the electrolyte in the cell. Pipe Il is supported in this cell by means of collar I 5 which in turn is supported by means of a plurality of rods Il extending from the sides of the collar I5 and 'connected to the .inside walls of cone t.V Two nn-shaped members or lugs I1 are welded on opposite sides of pipe Il and the bottom ends of element I1 rest upon the upper rim of collar il. Collar Il as shown in cross-section in Iilg. '4 is provided with two diametrically opposed semicylindrical protuberances I8. 'lhe size relationship between hns I1 and protuberances I8 is so arranged that when the pipe I l is rotated on its axis so as to bring the fins I1 in augment with protuberances Il, the tins will slide into said protuberances, whereby the pipe I3 may be loweredinthecell. Atthetopoiiins I1 areprovided stops I9 which engage with the upper edges of protuberances I8 thereby limiting the downward movement of pipe I 3. In the normal operation of the device, pipe Il rests on collar I 5 in the elevated position. When desired. pipe I 3 may be lowered so as to bring the graphite tube Il below the level of the electrolyte in the cell.

In the operation of the device just described. the cell provided with the inserted pipe I3 and its attachments is operated in the usual manner. The halogen gas evolved at the anode rises upward in hood C on the outside of the pipe I3. little or no gas tending to enter the lower end of-the pipe Il. The rapid rise of the gas in hood 6 and into dome 1 causes the liquid to rise in dome 1 some distance above the main level of the bath in the cell. The liquid spills over into pipe I3 by way of the slots in graphite tube Il and descends back toward the electrolysis zone of the cell by way of pipe Il. 'I'he gas is separated from the liquid at the time that the liquid ilow changes from an upward to a downward direction. Part of the gas escapes in the space oucsie of tube u, wnue une reminderY is aaengaged from the liquid inside tube I4. The disengaged gas is led oi! through pipe t. At the point where the gas is disengaged from the liquid around the periphery of tube I4, there is Va. rapid. and chiefly horizontal flow of. liquid through slots 2l into interior of tube I4 and apparently because of the rapid. flow of liquor at that point, there is substantially no splashing of the liquid in the dome 1. Hence, the apparatus may be operated for long periods of time without the necessity of cleaning frozen salt from dome 1 or pipe I. The liquid passing through the slots in tube I4 descends by way of tube I8 into the interior of the cell.

In the above described device, in place of a slotted graphite tube I4 we may use other forms of graphite tubes at the top of pipe I3. For ex' ample. in place of the vertical slots we may use staggered horizontal slots, round holes or various other types oi' openings. It is also possibleto carry out our invention by using a plain, unperforated graphite tube at the top of pipe II, for example graphite tube 2l as shown in Figure 5. In the latter case, the top of the graphite tube is arranged to be a relatively short distance above the electrolyte levelin the cell so as to `permit the rising liquid in dome 1 to readily overilow the edges of tube 20. If desired, the edges of the upper edge of tube 2l may be provided with serrations or slots. We'prefer, however. to use the slotted tube as exemplified by tube Il of the drawings since this has proven to give the best results in comparison with other types which have kbeen tried.

Thetubes I4 and 2l, as illustrated, or their equivalents are preferably made of graphite when the invention is used in a cell for the production.

of a corrosive gas such as chlorine. The invention is not restricted to graphite tubes, however,

since metal tubes are satisfactory when the gas being collected, e. g. hydrogen, is non-corrosive to metal. Moreover, other materials, not readily Y corroded by the gas evolved may be utilized to from the top of the circulation tube or equivalent means.

Ihe arrangement described above for lowering the pipe I3 by allowing the ns I1 to slide through the channels formed by protuberances I8 in collar I5 is useful when for any reason the cell temperature istemporarily lowered to such point that the upper surface of the fused electrolyte tends to freeze. .For example if it becomes necessary to shut ofi the powerfrom the cell for 'a short time, salt is likely to congeal in the upper portion of pipe I3, for examplein slots 2|. This may be avoided by lowering the pipe I3 so that slots 2| are well below the electrolyte surface.V

To lower pipe Il, a hook or other suitable tool may be inserted through dome 1 or pipe thy-way of an opening provided for the purpose and, for example, by engaging the tool with stops I9, pipe Il may be rotated to allow ns I1 to slide through channels I8 in collar I5.

The invention is not restricted to the particular arrangement of supporting ns I1 and collar I5 as shown and described above. For example, the collar I5 may be formedl in two semi-cylindrical parts, with two spaces or slots between each part or maybe a. split ring with a single slot, through which corresponding ilns or lugs on pipe I3 may pass. The stops I9 are not necessarily attached to ns I1 but may bevattached directly to pipe I3. Various other modifications will be apparent to the skilled mechanic.

areas 3 Tothoeefsmiliarwithths' and nirfaoebeIu-psevldedwithradiallydisposed offusedsalt-eleotrolysisoells. will vertiicslslbtsleadingintosaideomiuit.

invention is not restricted and further that it is not restricted to the employment 'of the particular device described and illustrated herein. In 'its broader aspect, our invention comprises providing an internal circulation of electrolyte in such manner that there is a rapid flow of electrolyte at the point where gas is diseikaged from the liquid electrolyte, this ilow being suiliciently rapid to overcome the tendency of the gas bubbles leaving the liquid to cause splashing and spattering.

be apparent that our to the Downrtype cell Various modiiications may be employed-to provide the particular type of internal bath circulation contemplated in the herein described invention. The vparticular means used to provide rising gas bubbles into the'required types of cells. In

circulation will vary with different the preferred modicationof 1 the invention, a gas collecting hood is constructedbeneath the electrolyte surface to bring the a zone of restricted crosssection, thus causing. a rise of liquid in said sone and providing means for rapidly flowing the liquid away at the surface of the rising liquid, either back into the lower parts of the cell or outside of the cell, preferably in a downward direction.

We claim:

l. In a fused salt electrolytic cell, a gas collecting device which comprises a gas collecting hood at least partially submerged in the electrolyte and adapted to collect gas arising from an electrode, gas outlet means connected to said hood and a substantially vertically disposed conduit located within said hood and extending from a point which is above the surface ofthe electrolyte outside of said hood, downwardly to a depth substantially below said surface.

2. In a fused salt electrolytic cell, a gas collecting device which comprises a gas collecting hood at least partially submerged in the electrolyte and adapted to collect gas arising from an electrode, gas outlet means connected to -said hood, a substantially vertically disposed conduit located within said hood and extending downward from a point above the electrolyte surface to a substantial depth below said surface, a portion of said conduit which lies above said surface being provided with openings leading into said conduit.

3. In a fused salt electrolytic cell, a gas collecting device which comprises a gas collecting hood at least partially submerged in the electrolyte and adapted to collect gas arising from an electrode, gas outlet means connected to said hood, a substantially vertically disposed conduit located within said hood and extending downward from a point above the electrolyte surface to a substantial depth below saidA surface, a portion of said conduit which lies above said surface being provided with radially disposed vertical slots leading into said conduit.

4. In a fused salt electrolytic cell, a gas col-y lecting device which comprises a conical gas collecting hood submerged in the electrolyte and adapted to collect gas arising from an electrode, a cylindrical gas collecting dome surmounting said hood: gas outlet means connected to said dome, a substantially vertically disposed conduit located within said hood and dome and extending downward from a point above the electrolyte surface to a substantial depth below said surface, a portion of said conduit which lies above said dome, a vertical, cylindrical, open tube concentric with said hood and extending from a point near the electrode at which the gas is formed upward into said dome above the main electrolyte level in the cell, a portion of said tube which lies in the gas collecting dome being provided with a plurality of openings leading into the tube.

6.Inafusedsaltelectrolyticcell,a'gascol lecting device which comprises a conical gas collecting hood submerged in the electrolyte and adapted to collect gas arising from an electrode, a cylindrical gas collecting dome surmounting said hood, gas outlet means connected to said dome, a vertical. cylindrical, open tube concentric with said hood and extending from a point near the electrode at which the gas is formed upward into said dome above the main electrolyte level in the cell. a portion of said tube which liesinthegascollectingdomebeingprovided with a plurality of vertical, radially arranged lies in the gas collecting dome being provided with a plurality of vertical, radially arranged slots adapted to lead electrolyte into said tube.

said tube being supported. by means of lugs attached to the -tube which rest upon the upper edge of a ring shaped member through which said tube passes, said ring-shaped member being provided with channels through which said lugs may pass when the tube is rotated to bring the lugs and channels into alignment, so as to lower the tube through said ring-shaped member.

8. In a fused salt electrolytic cell, a gas collecting device which comprises a conical gas collecting hood submerged in the electrolyte and 'adapted to collect gas arising from an electrode,

a cylindrical gas collecting dome surmountins said hood, gas outlet means connected to said dome, a vertical, cylindrical, open ytube concentric with said hood and extending from a point near the electrode at which the gas is formed upward into said dome above the main electrolyte level in the cell, a portion of said tube which lies in the gas vcollecting dome being provided fwith a plurality of vertical, radially arranged slots adapted to lead electrolyte into the tube, said tube being supported by means of lugs attached to the tube which rest upon the upper edgeof a ring-shaped member through which said tube passes, lsaid ring-shaped member being provided with channels through which said lugs may pass when the tube is rotated to bring said lugs and channels into alignment, so asto lower the tube through said ring-shaped member and said tube being provided with means for stopping the descent of 'said tube at a. predetermined level. Y.

9. In a fused salt electrolytic cell, a gas collecting device which comprises a conical gas collecting hood submerged in the electrolyte and adapted to collect gas arising from an electrode, a cylindrical gas collecting dome surmounting said hood, gas outlet means connected to said dome, a vertical, cylindrical, open tube concentric with said hood and extending from a point near the electrode at which the gas is formed upward into said dome above the main electrolyte level in the cell, a portion of said tube which lies in said gas collecting dome being provided with a plurality of vertical, radially arranged slots adapted to lead electrolyte into the tube, said tube being supported by means of a pair of diametrically disposed, vertical fins, the lower ends of which fins rest upon the upper edge of a ringshaped member through which said tube passes, said ring-shaped member being provided with channels through which said ns may pass when the tube is rotated to bring the ns and channels stream:I

into alignment, so ast@ lower thetube through said ring-shaped member and the upper endsl 10. A cell for fused salt electrolysis having an i electrode adapted to cause gas formation located beneath the surface of the electrolyte, a'gas collecting chamber located above thepoint of gas formation and partially submerged in the electrolyte, a conduit for owing electrolyte, together with gas formed at said electrode, upwardly within said chamber to a point of gas disengagement located above the surface of that electrolyte which is outside said conduit and another conduit for vflowing electrolyte from said point of gas disengagement downwardly within the cell back to said electrode.

ROBERT EDWIN HULSE. VIRGIL L. HANSLEY. HERMAN G. LAUGHLIN.

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