US2315443A - Electrolytic cell for fused baths - Google Patents

Description

Match 30, 1943. R. J. McNlT-r f l :ELECTROLYTIC CELL FOR FUSED BTHS Filed Nov. 18,V 1959V 2 Sheets-Sheet l www, ATTO RN EYS March 30, 1943. R. J. MGNITT,

ELECTROLYTIC CELL OR FUSED BA'I'HSv Filed Nov.v 1a, 1959r 2 sheets-sheet 2 e Patented Mar. 30, 1943 UNITED STATES PATENT QF'FlC-EA,

' ELEcrRoLYrrc cau. FOR FUsEn Barns Robert J. McNitt, Perth Amboy, N. J. Appiication November 1s, iaaajseral No. 305,212 1o claims. (o1. 2011-247) This invention relates to the electrolysisY of fused bathsand in particular to the production of light metals by the electrolysis of fused mixed baths, wherein the compound of the metal sought is fused with oneV `or more fiuxing substances to Alower the melting point. of the bath. In such electrolytic operationsV to which Vthis invention pertains, a' cathode stream of electrolyte circulates in the bath, flowing upward into the zone 'of .electrolytic action and downward past a surface of the cathode which lies4 outside of the zone of electrolytic action. This invention has for an object the provision of an `improved-method of, and apparatus for, effecting an improvedk circulation of the cathode stream of electrolyte.-

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f lytic cell;

I In the electrolysis of fused mixed baths'v it is important that there shall ble adequate circulation of the electrolyte to insure that in all parts of the zone of electrolytic action, the various constituents of the electrolyte shall always be present in suitable proportions.

In small cells satisfactory circulation of the electrolyte is maintained by convection currents therein. Heat liberated by the flow of electric current between the electrodes, raises the temperature and lowers the`density of the electrolyte in the zone of electrolytc action. In other parts ofthe cell, heat departs from the bath causing a fallin temperature and a rise in density. Due Vto this difference in density circulation of the bath occurs, upward at the active cathode surface, and downward in other parts of' the cell.`

This circulation has been found inadequate in I cells having cathodes of extensive area set close to the anode surface, as is desirable for maximum economy, and it is the aim of my invention to remove this limitation.

This invention aims to improve the circulation of the cathode stream of electrolyteV by repressing the flow of heat from the zone ofelec- Vtrolytic action into the downward streamf of electrolyte thereby increasing its rapidity of flow. To this end `I repress the-flow of heat by Vmeans of a thermal barrier imposed between the downward stream and the zone of electro.-

lytic action. Y I y The thermal barrier may consist of one or more solid walls or partitions together with one or more liquid or gaseous films or bodiessuch, for

example, as a partition having liquid or gaseous of the upward and downward stream. r`The thertween the bodyof the cathode, and the downward stream, or it may be in both positions. Y

As an example, I shalldescribe my invention as applied to a cell for the electrolytic production of sodiumfrom a fused bath consisting of sodium chloride,with one or more fluxing agents.

The accompanying drawings illustrate more or less 'diagrammatically apparatus embodying the invention, in which;

Fig. 1 is a vertical section through an electro- VFig. 2 is a horizontal section taken at line 2 2 of Fig. 1;

Fig. 3 is a fragmentaryvertical sectional view of a cathode'andv thermal barrier, and

Figs. 4, 5, 6 7 and 8 are fragmentary vertical sectional views of modified Aforms yof thermal barriers.k

As illustrated in thedrawings, the cell I comprises a steel shell oricontaining vessel 3 lined withlla refractory 4. 'A cylindrical graphite anode 5 having an activey surface A passes up through the bottom of the shell and isconcenf tric therewith. An annular steel cathode 6 Yhaving an active surface B and a .lessactiveer inactive surface C is mounted raround the anode and supported by two arms 1 which pass tlir/ough the cell wall and serve to conduct the Vfelectric .current from the cathode to the outside of thev cell. A cylindrical perforated diaphragm 8 is hung concentric with-the active cathode'and anode surfaces and is supported by a steel coillector `9 which is in turn suspended from beams (not shown) which rest on the top of theshell `3. The collector 9 serves to collect anddeliver fr om the cell the products of electrolysis, namely,

Vchlorine gas by way of the dome III and duct II and liquid sodium by wayof hood I2 and duct I3. Around the outside of the cathode 6, I place `a thermal barrier comprising a'composite partition I4 having a steel' vessel` I 5, filled :with a films adjacent thereto, or arpartition forming a passage containing a liquid maintained at tem- `in turn rests on the ltop of the cathode' 6;

Y thermal insulating material, such as diatomaceous earth',.and a steel skirt I6 .closed at the top suspended from asteelY angle ring Il, which The steel vessel I5 is inserted inside: the skirt -and is thereby enclosed ron` the sides and top.

yVessel I5 is closed at the bottom and on all sides, but is open at the top, while skirt I6 is closed against entrance of the molten bath at the top and on all sides, but is open at the `bottom.

In the type of cell shown, I prefer to make the thermal insulating .barrier I4 in two sections suspended from the angle ring I'I which may be lowered into position aftery the fused bath has been .prepared around the electrodes. Steel wings I8 serve to guide these sections to their proper positions, and also torclose the spaces between the-ends of the steel skirts-l6 and the cathode arms'fl. Y

The lcathode stream of electrolyte comprises an upward stream I9 and a downward stream 20. 'Ihe upward stream I9 passes between the factive., surface B of the cathode and thecliaphragm 8 in what has been referred to herein as the zone of electrolytic action, andthe downward stream 20 passes between the barriers I4 and the refractory lining 4. While there is electrolytic action between the surface A of the anode and the diaphragm, the zone of electro- -lytic action to which reference is made herein is between the active surface B of the cathode 6 and the diaphragm 8.

'I'he thermal partition I 4 taken alone, will effectively check the flow. the heat from the upward cathode stream of electrolyte I9 in the zone of electrolytic action, through the cathode body and into the downward stream .20 thusreduclng the counter .currents in the latter and, by permitting a greater difference in temperature and specific gravity between the rising andrfalling streams of electrolyte, result in a more effective circulation of replenished bath past the active cathode surface. I may, however, providea more enicient thermal barrier by spacing the thermal insulating partition I4 a short distance away from the cathode 6, thus forming passages 2| which are connected with the zone of electrolytic action by a lplurality of small openings 22 through the cathode. The relatively -cool replenished lelectrolyte entering these passages at the bottom 23, becomes lessdense as it absorbs heat throughthe cathode body 6, and rising in the passage flows through openings 22 into the zone of electrolytic action, taking the place of the electrolyte which has Ibeen decomposed by the electric current, and restoring to the electrolyte in the zone of electrolytic action most of the heat 'The thermal partition I4 includes a number of gaseous and liquid films which impede the flow of heat. Each of the vertical surfaces of the steel skirt I6, and the exterior surfaces of the yessel I5 have liquid films of electrolyte in contact therewith, and the interior vertical surfaces of the vessel I5 have gaseous films in contact therewith. In certain types of cells requiring a very substantial repression of the flow of heat, the thermal partition I4 as arranged in Fig. 1 is particularly desirable. In cells requiring a lower'repression of the iiow of heat into the downward stream, I may dispense. 'with one or more of the thermal insulating media comprising the complete partition I4. For example, I may emlploy vessels I5 in the barrier, with or Without the diatomaceous earth, and I may use the skirts I6 alone,.omitting the vessels I5 as shown in Fig. 4. f

Under certain operating conditions, the simple and effective thermal barrier illustrated in Fig. 3 may be used. This thermal barrier consists of asingle wall or partition of sheet steel 24 spaced from the outersurface of the cathode 6 forming the passage 2|. wall 24, two liquid films a'djacent thereto, and the stream of electrolyte in the passage 2|. In this operation, the rising stream of relatively cool electrolyte in passage 2 I, together with the liquid films and metal, afford ample repression of the flow of heat from the upward cathode stream I9v mit limited circulation of the stream of cool bath which escapes therefrom through the body of the r cathode. Moreover, the streams of cool bath flowing'up through passages 2| maintain a lower temperature at the surfaces of insulating Aparti-- tion I4 which are adjacent to the cathode than would be possible if the streams were not flowing through passages 2 I.

I prefer to space the openings 22 more closely together in the upper part of the cathode body and to make the bottom of the openings inclined at an angle greater than 35 degrees with the horizontal to avoid the accumulation of sedimentary matter therein.

By means of the combinationof the thermal insulating partition I4 and the auxiliary stream of electrolyte rising in passage 2I and feeding through openings 22 in the cathode into the zone of electrolytic action, I form an effective thermal barrier repressing the flow of heat from the rising stream of electrolyte in the zone of electrolyticV action, through the body of the cathode and into in-this passage. But this -method is much less (advantageous than the method 'in which the stream of bath in passage 2| flows through openings 22 in the cathode body. v

There are .advantages in combining the thermal insulating 'partition I4 of Fig. 1 with the form of construction illustrated in Fig. 3' to form ra thermal barrier of greater effectiveness.

'In other constructions, I may dispense with the passage 2| and the openings 22 and merely fasten a refractory thermal insulator to thefinactive side C of the cathode as shown in Fig. 5 in which the iron strap 30 secures the insulation 3| to the cathode. I may also insert .thermal insulation 33 in chambers provided in the body of the cathode as shown in Fig. 6. On the other hand, a passage 34, answering the same purpose as passage 2 I, may be provided in the body of the cathode with openings 35 similar to openings 22 leading to the zone of electrolytic action, and a thermal insulating partition 36 may be inserted between this passage and the downward stream 20 as shown in Fig. 7, if the conditions should be severe.

The thermal barriers illustrated in the draw ings extend throughout the length of the 4cathode and in most operations this is the preferred form of barrier. It is understood, however, thatv the barriers need not, for all purposes, extend the full length of the cathode, and the invention includes barriers that are relatively short as compared to the cathode. The upper portion ofthe thermal barrier has a pronounced effect upon the transfer of heatand I may accordingly use relatively short barriers, for example, a barrier 31 whichis less than half the length ofthe cathode as shown in Fig. 8.

'Ihis barrier includes the metal I claimil l. In/a cell for Ythe electrolysis of fused 'mixed baths -having a cathodaananode anda diaphragm between the anode`a11d the cathode,the active surfaces of the cathode and the anode being varrangedvin upright positionsproviding a narrow upright space therebetweenpan upright v space along the inactive side of the; cathode connecting bothl abovel and belov'vftlie cathode with the narrow upright space, said cell being arranged to be sooperated that a vstream of electro-f lyte circulates inal loop'upward in theupright narrow space between the active sidel of the cathode and the diaphragm and downward in the upright space along the inactive side of the cathode, the improvement which comprises a thermal barrier including a partition arranged between the inactive side of the cathode and the downward stream of electrolyte extending substantially the length of the cathode and so spaced therefrom that a part of the stream of electrolyte flows into the space between the thermal bare rier and the cathode, and a plurality of openings in the cathode through which the stream of elec. trolyte in the space between the thermal barrier and the cathode flows into thev upright narrow space between the active surface of thercathode and the diaphragm. Y

2. A cell for the electrolysis of fused mixed baths which comprises a receptacle for the bath, an upright anode, an upright cathode having a plurality of spaced openings therethrough, an

upright diaphragm spacedV between the active surfaces of the anode and the cathode, an upright partition extending along the inactive surface of the cathoderfrom the top toward` the bottom thereof, an 'upright space betweenthe cathode and the partition, a member closingthe space at the upper parts of the cathode and theA partition, `a passageway through which the hot cathode stream ofA electrolyte flowing upward between the cathode and diaphragm flows over the top of the cathode and partition and' downward along the partition, and passage means permitting a part of the downward'stream to pass .into the space between the cathode and the partition and through the openings and another part the topofthe metal plate and the cathode, and

a plurallty'o'f Vholes in the said means permitting the passage therethrough ofv a stream of electroandthe inactive .surface of the cathode.

5;*A-cell', for the electrolysis of fused lmixed baths which comprises an upright anode, an up- ,lytejrisin'g in'jthe space betweenthe metal plate right cathode, an upright 4diaphragm' spaced between the active surfaces ofthe anode and the` cathode, an upright thermal barrier mounted near the inactiveside of the cathode proportioned and arranged'to extend over substantially the entire inactive sideof the cathode, an upright walljspaced from the thermalrbarrier forming a passageway between the wall a'nd the thermal barrier for the downward flow of electolyte, "said thermal barrier comprising'a plurality of spaced upright metal plates, and a thermal -l insulating medium between atleast two of the plates, whereby the flow of heat from the cathode finto the electrolyte the passageway is suppressed.

6. A cell for the electrolysis of fused mixed baths-which comprises an upright anode, an upright cathode, an lupright diaphragm spaced be- 'near the inactive side of the cathode, said thermal barrier comprising a plurality of spaced upright thereof topass upward between the cathode and the diaphragm.

3. A cell for the electrolysis of fused mixedbaths which comprises an upright anode, an upright cathode, an upright diaphragm spaced betweenvthe active surfaces of the anode and the cathode, a plurality of spaced openings in the cathode, a wall spaced from and extending along the inactive surface of the cathode, and an upright thermal barrier comprising a metal plate right passage along the' inactive side of the cathode, and another passage between the thermal barrier and the wall. I

4., A cell for the electrolysis of fused mixed baths which comprises an upright anode, an upright cathode, anupright diaphragm spaced between the active surfaces of the anode and the cathode, an upright wall extending along and spaced fromy the inactive surface ofthe cathode forming a passageway through which electrolyte flows downward, an upright thermal barrier Ain the Vsaid passageway comprising a metal plateextending from'the top of the cathode towards the bottom and spaced 'from the inactive surface of the cathode, 'means closing the space between l of the cathode and Abetween the upward and `spaced between the wall and the inactive surface i of the cathode extending throughout the greater part of the length of the cathode forming an upmetal plates, a space between at least two of the plates for confining a gas, and another thermal insulating medium enclosed between two of the plates, whereby the flow of heat from the cathode into the electrolyte in the passageway is suppressed.

r7. 1n a'ceu for. the electrolysis of fused baths l having an anode, ja cathode and a diaphragm arranged in upright positions and so spaced from .'eacrh other as to form a narrow passageway be- J`tween the diaphragm and the active surface of the cathode and another passageway along the inactive surface of the cathodeand opening means connecting the said passageways both above and below the cathode, whereby the same stream of electrolyte may VflowV upward in/the narrow passageway and downward inthe other passageway, the improvement which comprises aV thermal barrier mounted near the inactive side downward streams which 1s constructed and arranged to repress the flow of heat from the electrolyte on thev active side of the cathode through the cathode to the electrolyte along the inactive side of the cathode.

8. In the electrolytic cell according to claim 7, said thermal vbarrie'r comprising a plurality of insulating media including solid and fluid materials.

9. In a cell for the electrolysis of fused baths having a cathode, an anode and a diaphragm ar-v ranged in 'upright positions and so spaced from each other as to form a narrow passageway beween the diaphragm andthe active surface of the cathode and another passageway valong the inactive surface of the cathode and opening means vconnecting the said passagewaysy both above and below the cathode. whereby the same streamof electrolyte may 'now upward in the narrow passageway and downward in the other passageway, the improvement which comprises a lmetal partition placed along and spaced from the inactive surface ofthe cathode and between the upward and downward streams to provide apassage in which molten electrolyte may enter, `said partition and molten electrolyte in the passage comprising a thermal barrier which represses the flow o f heat through the cathode.

10. In a. cell for the electrolysis of fused salt vbaths having an upright cathode, an upright anode and an upright diaphragm between the anode and the cathode, the active surface of the cathode and the diaphragm being arranged in upright positions providing a narrow upright space therebetween, an upright wall laterally spaced fromY the cathode forming an upright space along the inactive side of the cathode con- A"necting both above and below the cathode with iyte-in the upright space along the inactive surface.

'ROBERT J. MCNI'I'I.

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