US951228A - Method of decomposing salts. - Google Patents

Description

J. WHITING. METHOD 0F DECOMPOSING SALTS. APPLICATION FILED DBO. 1e, 1908.

y95 1 ,228. n Patented Mar. 8, 1910.

lleve/for J. WHITIN G. METHOD OP DEGOMPOSING SALTS.

4APPLICATION FILED DBO.16, 1908.

Patented Mar. 8, 1910.

3 SHEETS-SHEET Z..

fra/6705021- J. WHITING. METHOD 0F DECOMPOSING SALTS. APPLICATION FILED 1320.16, 190B.

Patented Mar. 8, 1910.

3 SHEETS-SHEET 3.

UNITED scares. PATENT JASPER WRITING, 0F BOSTON, MASSACHUSETTS, ASSIGNOR TO PANY, 0F BOSTON, MASSACHUSETTS, CORPORATION carica .0F MAINE.

METHOD OF DECOMPOSING SALTS.

Specification of Letters Patent. Application filed December 16, 190,8; Serial No.

Patented Mar. 8, 1910. 467,846.

To all rwhom t may concern:

Be it known that I, JAsPER'WHITING, a citizen of the United States, residing at Boston, in the county of Suffolk and State of Massachusetts, have invented certain new and useful Improvements in Methods .of Decomposing Salts, of which the following is a specification.

This invention relates to the electrolytic decomposition of salts by methods involving the employment as cathode of a body of liquid metal or alloy. In Amethods of this character it has been usual maintain a substantially continuous circulation of the cathode, but this practice has proven objectionable by reason of the tendency of the .electrolytically separated metal, as sodium, to become oxidized and to renter into solution in the decomposing compartment. For example, in the production of caustic soda by electrolysis of aqueous solutions of sodium chlorid in presence of a mercury cathode, the sodium amalgam tends to collect at the cathode and its removal to the oxidizi compartment is only incompletely effected by the flow of the underlying body of mercury; the sodium of the amalgam is therefore subject to oxidationby the electrolyte undergoing decom osition, resulting in a reduced efiiciency oP operation.

In my prior patent'No. 877,537, .granted January 28, 1908', I .have described a method of electrolyzing salts wherein .a cathode of liquid metal or alloy is maintained in a quiescent state during the period of electrodeposition therein of an alkali .or .otherA metal, the cathode .being periodically conveyed from the decomposlng compartment to a suitable oxidizing compartment, and re-A turned to said decomposing compartment, the How of the electric current bein preferably maintained without'interruptlon by the provision of a plurali-ty of bodies of the f' cathode metal adapted to .be conveyed in succession to the oxidizing compartment or compartments. As described in saidV patent, the contents of the decomposing and oxidizing compartments are .in .balanced relation, and the metal or alloy which is discharged heretofore to surface .of the mercury lbody of cement, concrete or ment is conveyed to a pump or equivalent ydevice by means of which it is elevated and discharged into the oxidizing compartment,

the denuded metal flowing thence by gravity to the decomposing compartment where its content .of alkali metal is restored.

According to the present invention the liquid metal is also maintained in a state of rest during the charging period or period duri which the sodium .or other metal is deposited therein, but is at appropriate intervals transferred by gravity .to a region of oxidation, the denuded or purified metal being thereafter returned to lthe decomposing compartment.` In the preferred embodiment of the invention the alloy or amalgam from the decomposing compartment is permitted to flow through the oxidizing compartment in contact with carbon surfaces and anxoxidizingV electrolyte. By .this procedure several important .advantages are secured as hereinafterset forth.

For a full understanding ofthe invention the same will be described by reference to the production of caustic soda by .the electrolytic decomposition of an aqueous solution .of sodium chlorid in the presence .of .a cathode of mercury.

A preferred form trated in,`

Figure l is a longitudinal section on line l-1 of Fig. 3; Fig. 2 is aside elevation of the apparatus; Fig. 3 is a plan view Vof the same; Fig. 4 is a transverse vertical section on the broken line 4 4 lof Fig. 3; and Fig. 5 is a vertical sectional view .of a preferred form of elevating .device .or pump for the mercury.

Referring to the drawings 1 represents a other suitable material, in .which Vare formed one or more' decomposing .compartments 2 and an oxi- 'zing--compartment 3. As illustrated, I preferably .provide a plurality of mechanically separated bodies of mercury contained in shallow basins 4, shown as 'five .in number, formed in the bottom Aof the decom osing compartment 2.: Ait .will lbe un'derstoo` :how-

of apparatus is illus- 1n the accompa-nymg drawnig where- AT111: WRITING oo lvr- Y ever that a single body of mercury or any desired number of bodies may be provided in the decomposingcompartment These basins may be lined with glass, slate or 'earthenware 5 and are separated from each other by low partitions 6 set in the cement base and extending above thqe normal surface of the mercury cathode, the arrangement providing a common body of electrolyte above the several separated bodies of mercury. 7 is a similar partition disposed transversely of the basins 4 and near one end thereof in such manner as to provide an equalizing channel 8 from which the mercury may flow to the several basins, this equalizin channel being sup lied with mercury rom a distributing con uit 9 which receives the denuded metal from the oxidizing compartment.

Above each basin is disposed an anode or anodes 10, which may be vertically slotted as indicated at 11 to permit the escape of chlorin. These anodes are usually of graphite and are carried at one end by a ledge 12 inte al with the cell body, and at the other by t e partition 7 The anodes preferably extend over the mercury in the equalizing channel as shown in suchy manner as to conf this arrangement permittingthe stitute the mercury therein ,a part of the active cathode, whereby the capacity of the cell is increased to a corresponding extent. The several anodes are electrlcally connected in circuit through graphite leads 13 extending upwardly through the cover 14 of the decomposing compartment.` The cover 14 is removable together with'the anodes,

ready opening of the cell for inspection, cleaning orY the repair or replacement of parts.

Centrally disposed in the bottom of each basin 4 is a longitudinal slot or channel 15, the mercury in which is in electrical contactwith suitable conductors 16 which are embedded in the body 1 and are connected to the cathode bus bars 17; The slots 15 ineline downwardly tothe discharge end of the cell, and communicate at their lower ends with conduits 18 through which the amalgam may be discharged .into the oxidizing compartment 3. t the bottom of. each slot are shown a llurality ofwells 15a adapted to retain smaliivolumes of mercury protect the metallic conducting plates16 and to establish electrical contact between them and the overlying anaal-- Gam. Each slot terminates at its lower end 1nI a pocket 15b, the construction being such as to permit the mercury to be discharged from the cell or compartment with substantial completenes Each conduit 18 is prov1ded at its discharge end with a weighted valve 19 normally closing the same but 4adapted to be opened at desired intervals eral channels, the denuded -tact with the water or loxidizing the members 33 being disposed to permit a at 36 in by the movement of.levers 20, actuated by cams 21, carried by a rotary shaft 22. The valves 19 are guided to their seats by downward projections 19a. As illustrated, they are suspended by chains 19h, and an adjusting screw 19c is provided by means of which the lift of the valve may be varied as desired. It will be understood however that the invention is not restricted to the particular means illustrated for operating the valves at the desired or predetermined intervals. When the valves 19 are opened the mercury or amalgam in the respective basins of the decomposing compartment liows by gravity upon the inclined surfaces 23 (Figs. 3 and 4) and thence through channels 24 to the oxidizing compartment 3.

In the particular form of apparatus illustrated, the oxidizing compartment comprises a series of wide shallow disposed at successively lower levels and separated by partitions 28 so arranged that the amalgam is directed in a tortuous path as indicated by the arrows through the s evinally to the sump 29 (Fig. 5). It is then elevatedv by a rotary disk pump 30and returned by conduit 31 (Figs: 2, 3) to the distributing conduit 9, passing thence to the equalizing channel 8 and the proper basin of the decomposing com artment.

As indicated in Figs. land 3 the bottom of each of the channels 25, 26, 27 of the oxidizing compartment is constituted by a carbon or graphite slab 32, having integral members 33 .projecting upwardly into conelectrolyte,

ready iow of the amalgam while providing a maximum contact therewith. The oxidizing compartment is supplied with water, the caustic soda solution escaping through an outliow 34..

AIt is important that the denuded mercury should be freed from 'adhering or mechanically conveyed caustic soda solution before rentering the decomposing compartment.

In the present construction this may be ac-,

complished by the provision of traps or seals of any ordinary type in the conduits 31 and 9. Thus I have illustrated in Fig. 2 a trap or seal 35 arranged in connection with the discharge line of the pump .30 and serving to retain the supernatant liquid While permitting the iow of the mercury. A similar arrangement comprising a partition extending below the surface of the mercury in distributing conduit 9 is indicated readily be washed and thereby thoroughly freed from alkaline constituents by the introduction of water into the conduit 31 at a point intermediate these seals, as at 37 Fig. 3. 1f desired the mercury may` channels 25,26, 27

mercury flowing (Figs. 2, 3), this water overflowing at 38 into the oxidizing compartment 3 and serving as a source of supply therefor.

For elevating the denuded mercury from the sump 29 to the conduit 31 leading to the decomposing compartment, I have illustrated a rotary disk pump 30 provided with peripheral inlet apertures 39 leading to internal pockets 40 (Fig. 5), from which the mercury is discharged laterally through conduits 41 as thepockets are brought successively'into proper relation to a trough 42, leading to the conduit- 31. As shown, the pump 30 is mounted on a shaft 43 carrying a sprocket 44, driven by a chain 45 from a sprocket 46 on a shaft 47 having a clutch connection 48 with a power shaft. This apparatus for elevating the mercury is found to operatevwithout such agitation of the metal as would result in its subdivision into globules With consequent danger of loss,

and is claimed in my co-pending application, Ser. N o. 467,848, filed December 16, 1908.

I prefer to provide in connection with the cell an intermittently operating device for supplying the electrolyte to the decomposing compartment, this device being automatic in character and permitting the electrolyte to flow into the several basins of the decomposing compartment only while the mercury or amalgam is `absent therefrom or substantially so, that is to say, while the electrodeposition of sodium is not in progress, thereby avoiding all tendency to disturb the surface layer of amalgam and to reoxidize the deposited alkali metal. As herein illustrated this feed device comprises a plurality of receptacles 49 disposed -in the cover of the cell above the respective basins 4, and interconnected by open channels 50. From the bottom of each receptacle 49 a tube 51 extends downwardly below the normal surface of the mercury in the basins 4 in such manner as to be sealed thereby. Electrolyte is supplied to one of the receptacles 49l and conveyed by the equalizing channels 50 to each of the others, any `excess being permitted to return to the circulating system, or if desired to How continuously into the decomposing compartment as through conduit 52.

ySo long as the several basins 4 contain sufficient mercury to seal the lower ends of the discharge tubes 51, the electrolyte is prevented from flowing therethrough, but when the mercury is discharged from any basin into the oxidizing compartment this seal is broken and a quantity of electrolyte corresponding approx1mately to the 'capacity of the receptacle 49 ows into the decomposing compartment. f By this arrangement the fresh electrolyte is introduced at the bottom of the cell beneath the. body of partially spent andconsequently lighter elecalkali metal. -The electrolyte may however .n

beco'ntinuously fed to the decomposing compartment under any conditions which will not so agitate or disturb thebody of electrolyte as to cause undue rcoxidation of the alkali metal. The above described means for introducing electrolyte is claimed in my copending application, Ser. No. 467,847, tiled December 16, 1908.

In the operation of the apparatus described the mercury in the several basins 4 beneath a common body of electrolyte in the decomposing compartment 2 remains in a quiescent state during the charging period, that is to say the period during which the sodium is being electrically deposited, and is therefore under the most favorable conditions as regards efficiency of operation. At the conclusion of the electrodepositing or charging period, 'when the mercury has received the desired quantity of sodium, the valve 19 controlling the outflow of one of the basins is raised by the corresponding cam 21, and the entire body of amalgam in this basin, with the exception of such small quantity as is required to maintain a seal in the conduit 18 between the decomposing and oxidizing compartments, flows rapidly by gravity but without serious agitation to the oxidizin compartment 3, tra-verses the same and is t ereby denuded of its alkali metal. The pure mercury is then conveyed by pump 30 to the conduit 31 and thence through conduit 9 and equalizing channel 8 to the decomposing compartment, flowing as will be understood into an empty or discharged basin, in preference to one containing -mercury. By the slow rotation of the shaft 22 the next cam 21l will after an appropriate interval be brought into position to raise the valve 19 of the basin next in series, the operation continuing in such manner that the mercury in the several basins 4 is discharged in rotation and at proper intervals, denuded of its alkali meta-l, and returned to the decomposing compartment. As'the amalgam is dlscharged from each basin a bodyof fresh electrolyte is introduced through the tube 51 beneath the body of partially spent electrolyte therein, thereby maintaining the required degree of saturation of the electrolyte. lVhile the liquid cathode is maintained during the charging period in a state of rest, it will be observed that during the oxidizing period it is causedto flow in contact 'with carbon surfaces and an oxidizin electrolyte, thereby providing the most e4 .fective conditions for completely denuding it of its content of alkali metal.

The herein described method possesses several important advantages over that described in my prior patent, No. 877,537, above referred to, these advantages following chiefly from the mode of o erationl which permits the amalgam to flow y gravity from the decomposin to the oxidizing compartment instead of eing elevated to the oxidizing compartment and being permitted to flow by gravity therefrom to the decomposing compartment. Amon s uch advantages are the following :-(1) uring the charging eriod the mercury and superposed electro yte in the decomposing coinpartment is mechanically separated from that in the oxidizing compartment instead of being in balanced Jrelation therewith, whereby it is not subject tofluctuatibn in level or variation in quantity due to the changes in the relative' density of the electrolytes or in the pressure of the evolved gases: therefore more nearly constant current conditions may be maintained and the general operation of the cell improved. (2) There is less liability to the conveyance of caustic soda or other alkaline constituents from the oxidizing to the decom osing compartments,.the flow of the denud) to the decomposing compartment being tortuous, involving passage through a pumpor elevating device and providing opportunities for further purifying operations to be performed upon it. (3) The arrangement permits the equalizing channel for the mercury to be placed within the decomposing compartment, thereby renderin the mercury in this channel available for use as a part of the cathode and correspondingly increasing the cell capacity. (4) The method provides for the pumping of pure mercury instead of amalgam, this being advantageous as avoiding all tendenc to the formation of incrustations outside ol the oxidizing chamber. (5) The construction is such'as to permit the mercury to be discharged with sub,

stantial completeness from the decomposing cell or compartment.l (6) The cell is more compact, more economical as regards the use of mercury, and of simpler and less expensive construction.

' I claim:

1. The method of decomposing salts which consists in passing an electric current through an electrolyte to a quiescent body of liquidmetal as cathode, transferring said body by gravity to a region of oxidation, and returning ed mercury t the denuded metal to the' lregion of electrolytic decomposition.

2. The method of decomposing salts which consists in passin an electric current through an electro yte to a plurality of quiescent bodies of liquid metal as cathode, transferring said bodies successively by gravity to a region of oxidation, and sup-- plying denuded metal to the region of electrolytic decomposition. n

3. The method of decomposing salts which consists in assing an electric current through an e ectrolyte to a quiescent body ofliquid metal as cathode, transferring said body by gravity to a region of oxidation, imparting motion to said body during the oxidation, and suppl ing denuded'metal to the region of electrofytic decomposition.

4. Tllie method of decomposing salts which consists in passing an electric current through an electrolyte to a plurality of quiescent bodies of liquid metal as'cathode,

transferring said bodies successively byA gravity to a common region of oxidation and supplying denuded metal to the region of electrolytic decomposition.

5. The method of decomposingsalts which consists in passing an electric current through an electrolyte to a quiescent body of liquid metal as cathode, transferring said body by gravity to a region of oxidation,

maintaining in said regionv of oxidation a y continuous flow of liquid metal or alloy, and supplying denuded metal to the region of electrolytic decomposition.

6. The method of decomposing salts which consists in passing an electric current through Aan electrolyte toa quiescent body of liquid metal as cathode, transferring said body by gravity to a region of oxidation,

elevating the denuded metal and returning it to the re ion of electrolytic decomposition.

7. The e ectrolytic method of decomposing alkali metalv salts which consists in alternately charging a body of liquid metal with an alkali metal and freeing it therefrom, maintaining the .liquid metal at rest during the charging period and causing it to flow in contact with a carbon surface and an electrolyte while freeing it from the alkali A metal.

8. The cyclical electrolytic method of decomposing alkali metal salts which 'consists in alternately and repeatedly charging a body of liquid metal with an alkali metal and freeing it therefrom, maintaining 4the liquid metal at rest durin the charging period and causing it to ow in contact with a carbon surface and an electrolyte while freeing it from the alkali metal.

9. The method of electrolyzing salts with a liquid metal cathode which consists in providing decomposing and oxidizin compartments containing inde endent bo ies of iquid metal, passing an e ectric current to u plurality of quiescent bodies of liquid metal in the decomposing compartment, transferring said bodies successively by gravity to the oxidizing compartment, and supplying denuded metal to the decomposing compartment.

10. The method of electrolyzing salts with a liquid metal cathode which consists in pro viding decomposing and oxidizing compartments containing electrically indepen'dent bodies of liquid metal7 passing an electric current to the body of metal in the decomposing compartment, transferring said body by gravity to the oxidizing compartment, permitting it to flow therethrough in contact With a carbon surface and an oxidizing electrolyte, and returning the denuded metal t0 the decomposing compartment.

In testimony whereof, Iy affix my signature in presence of tWo Witnesses.

JASPER WHITING. Witnesses:

' JOHN G. PALFREY, BERTHA S. CHASE.

Images