US2893940A

US2893940A - Fused salt electrolytic cell

Info

Publication number: US2893940A
Application number: US641290A
Authority: US
Inventors: Frank E Smith
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1957-02-20
Filing date: 1957-02-20
Publication date: 1959-07-07
Anticipated expiration: 1976-07-07
Also published as: FR1189525A; GB818840A

Description

y 1959 F. E. SMITH FUSED SALT ELECTROLYTIC CELL 3 Sheets-Sheet 1 Filed Feb. 20, 1957 INVENTOR.

Fran k E. Sm 'nfl wry/QM AGENT July '7, 1959 F. E. SMITH FUSED SALT ELECTROLYTIC CELL 3 Sheets-Sheet 2 Filed Feb. 20, 1957 FIG-4.

INVENTOR.

E1. Smi+h Frank Jufly 7, 1959 F. E. SMITH 2,893,940

FUSED SALT ELECTROLYTIC CELL.

Filed Feb. 20, 1957 3 Sheets-Sheet 3 INVENTOR. FranK E. SmN-h BY 9 QM A,

AGENT ti ttes FUSED SALT ELECTROLYTIC CELL Application February 20, 1957, Serial No. 641,290

4 Claims. (Cl. 204-243) This invention relates to an improvement in the graphite anode assembly in a fused salt cell especially a cell useful for the electrolytic production of sodium.

The Downs type of cell (U.S.P. 1,501,756), which is basic to present commercial product of sodium, requires that the anode due to its central arrangement must make contact with the electric current through the bottom below the electrolyte in the cell. For eflicient production it is necessary to keep the distance between anode and cathode at preferably not to exceed about two inches. Since the area between the electrodes is quite extensive and since it is necessary to operate with a metal diaphragm which must not contact either of them it is apparent that the electrodes must be in good alignment and must remain so for a long time if the cell is to have a satisfactory operating life. This difiiculty of maintaining correct alignment is especially aggravated if the cell is operated with multiple anodes.

Since the electrolyte in the cell must be maintained above its fusion temperature, approximately at about 600 C., it will be evident that the parts of the cell will expand on heating to the operating temperatures. Therefore, since the metal and non-metal parts, especially graphite and steel or iron have dilferent expansion coefiicients, there is an undesirably great tendency for the anode and cathode to lose their alignment with respect to each other as the cell is heated from room temperature to operating temperature. This is especially aggravated by the fact that the base of the cell must support the anode in its vertical position and at proper spacing from the other elements of the cell. The steel expands to 7 times as much as graphite with a given rise in temperature and often the alignment shifts so far that the diaphragm cannot be properly centered in the cell between the electrodes without causing electric shorts or causing disproportion of the anolyte and catholyte zones or both with consequent poor production and generally shortened cell life.

It is accordingly an object of the present invention to provide an improved electrolytic cell for the production of sodium. Another object is an improved arrangement of cell parts, especially an arrangement whereby the anode will better retain its alignment with the cathode and the diaphragm. A further object is to provide for better contact of the anode with the electric current.

These and other objects are accomplished by fitting and anchoring the anode by direct and positive means into a graphite base block, preferably rectangular, so arranged that differential expansion of metal and graphite parts will not interfere with the internal alignment between the anode on the one hand and the cathode, diaphragm and product collector system on the other.

My invention is illustrated by the drawing in which:

Figure 1 shows an arrangement of the anode base together with the electrodes and collector system in cross section suitable for a multiple anode fused salt sodium cell.

2,893,940 Patented July 7, 1959 JCC Figure 2 shows a horizontal cross section of the anode base block at XX of Figure 1.

Figure 3 shows a horizontal cross section of the cell at YY of Figure 1.

Figure 4 shows in vertical cross section an alternate method for fastening the anode to the base block.

The vertical graphite anodes 1 are tapered conically at their base ends which fit accurately into corresponding conical cuts or sockets in base block 2 also made of graphite. The anodes are further anchored in fixed centered positions in the block by means of graphite pins 3. The graphite base block 2 is held securely in steel base box 4 whose flange 5 rests on insulators 6 which support the shell 7 of the cell as well as the base box. The steel base box 4 will conform to the shape of the graphite base block 2 so that the latter will be held so secure that it cannot shift therein. The insulators 6 may rest on supporting beams 9. Metal wings 8 welded to the base box 4 serve as contacts with the electric busbar not shown. A metal which will be liquid at operating temperatures of the cell, such as Woods metal, as disclosed in United States Patent 2,592,483, in the space 10 between the graphite base block 2 and the base box 4 provides elfective electrical conductivity therebetween. An insulating refractory block 11 cast in place from a refractory cement seals the bottom of the cell from zone 12 containing the fused salt bath.

The base block 2 is held tightly in steel base box 4 so that the block is held so rigid that the anode anchored therein will remain in proper alignment with the cathode during the life of the cell. The graphite base block assembly with the anode is further anchored in place by the insulating block 11 which is preferably cast in place after the anode and the cell block 2 have been properly aligned and fixed in place by the steel base box 4.

. The anodes 1 in the cell bath are surrounded by steel cathodes 13 which by means of leads 14 which pass through the side of the cell establish contact with electric busbars not shown. The cathode leads 14 are electrically insulated by ceramic bricks and ceramic cement at 15 and ceramic cell lining or bricks 16 insulate the cell wall from the electrolyte. Annular diaphragms 17 between the electrodes are suspended from the product collector system comprising the sodium collectors 18 and the chlorine collectors 19. The cathode leads are connected as by welding by stubs 26 to the circular cathodes 13. At points 25 where the cathodes contact each other they are preferably welded together for good electrical contact and rigidity.

In Figure 4 anode 21 is integrated with or attached to the base block 2 by means of threads 23 at the bottom end which in turns fits into a corresponding opening in the block also provided with suitable threads 24 to receive the threaded anode end in a secure and tight fit.

Preferably the base graphite block consists of a single piece of graphite, however, where multiple anodes are assembled in a single cell it is possible to use a rectangular base block for each anode but the blocks must then be fitted together to fit tightly into the base box and of an area sufficiently large to serve as a base for the entire group of anodes. The base block must be sufiiciently thick and of suflicient cross section to permit cutting the proper openings for integrally fitting and anchoring the bottom anode end therein and to have suflicient mechanical strength as well as contact area to conduct the necessary current of electricity. In general, the block vertical thickness related to the anode length should not be less than about 1 to 10. The ratio of block thickness to anode length is preferably 1 to 5 but may be as great as .1 to 2 but there is very little advantage in such short anodes. The base block may be rectangular, octagonal or evencylindrical but its horizontal cross section must be large enough to exceed the cylindrical cross section of the anode.

The cylindrical axis of the anode should be centered at a-right angle to the horizontal cross sectional area of the base block and the circular diameter of the anode should be smaller than the width of the square area of the block supporting the anode. Preferably the circular diameter of the anode should be at least about 5% shorter than the side of the corresponding square or cross section of whatever shape of the base block supporting said anode and between about 20% and 30% shorter is preferred.

Various methods for fastening the anode to the base block may be used. Figure 4 illustrates a threaded union. Another union can be effected by a slotted opening in the base block into which a corresponding peg of the anode base is fitted. Other methods may also be used but I have foundthat the truncated conical fit illustrated by Figure 1 is much to be preferred since it lends itself to accurate cutting and fitting.

In general, it will be advisable to secure the anode in the conical cut in the base block by graphite pins fitted so as to securely fasten the base block and the conical end of the anode.

There is considerable latitude in the angle of the conical fit between the anode base and the base block. An angle between about 3 and 15 from the vertical will be practical but it is preferred that the angle be between about 7 and 10.

My novel method of arranging the anode in a graphite block so as to secure permanent alignment of the anode with the cathode and the diaphragm is applicable to salt cells provided with a single centrally arranged anode or with cells provided with a plurality of cylindrical anodes.

I claim:

1. In a fused salt electrolytic cell the combination comprising a bottom entrant carbonaceous cylindrical anode, the lower end of said anode fastened integrally into a carbonaceous rectangular base block, said block having horizontal dimensions greater than the cylindrical diameter of said anode, the lower end of said anode being anchored directly within said block, said block providing a firm support adapted to hold said anode in vertical position, said block adapted to serve as an efiective electrical conductor between said anode and the source of electrical power for said cell.

2. In a fused salt electrolytic cell the combination comprising a rectangular graphite base adapted to make contact with a source of power for electrolysis, said base being electrically insulated from ground and from the cell, a vertical tapered conical cut into said base, an elongated cylindrical graphite anode with lower end adapted to fit in exactly centered vertical position in said conical cut and thereby establishing electrical contact with said base, said base having horizontal dimensions greater than the diameter of said anode.

3. In a fused salt electrolytic cell with submerged graphite anode making electrical contact at the bottom of the cell the combination comprising a horizontally disposed graphite base block making electrical contact with a metal support for said block and a cylindrical anode with the lower end of said anode fitted rigidly into said block at right angle thereto, said block having horizontal dimensions greater than the diameter of said anode.

4. In a fused salt electrolytic cell with submerged anode making electrical contact at the bottom of the cell the combination comprising a horizontally disposed graphite baseblock making electrical contact with a metal support surrounding the sides and bottom of said block and a cylindrical anode with bottom end fitted rigidly at right angle into said block, the ratio of the vertical dimension of said block to the length of said cylindrical anode being greater than about 1 to 10 and said base block has a horizontal dimension at least 5% greater than the cylindrical diameter of the anode.

References Cited in the file of this patent UNITED STATES PATENTS 1,501,756 Downs July 15, 1924 2,213,073 McNitt Aug. 27, 1940 2,407,691 Suchy et al Sept. 17, 1946 2,592,483 Smith et al. Apr. 8, 1952 2,648,631 Carlisle Aug. 11, 1953 2,773,825 Necombe Dec. 11, 1956 FOREIGN PATENTS "451,444 Italy Mar. 10, 1949

Claims

1. IN A FUSED SALT ELECTROLYTIC CELL THE COMBINATION COMPRISING A BOTTOM ENTRANT CARBONACEOUS CYLINDRICAL ANODE, THE LOWER END OF SAID ANODE FASTENED INTEGRALLY INTO A CARBONACEOUS RECTANGULAR BASE BLOCK, SAID BLOCK HAVING HORIZONTAL DIMENSIONS GREATER THAN THE CYLINDRICAL DIAMETER OF SAID ANODE, THE LOWER END OF SAID ANODE BEING ANCHORED DIRECTLY WITHIN SAID BLOCK, SAID BLOCK PROVIDING A FIRM SUPPORT ADAPTED TO HOLD SAID ANODE IN VERTICAL POSITION SAID BLOCK ADAPTED TO SERVE AS AN EFFECTIVE ELECTRICAL