US2962433A - Fused salt electrolysis cell - Google Patents

Description

Nov. 29, 1960 J. DQMUELLQER' EI'AL FUSED SALT'ELECTROLYSIS- CELL Filed Dec. 23, 1958 Nov. 29, 1960 J. D. MUELLER ETAL 2,962,433

FUSED SALT ELECTROLYSIS CELL 2 Sheets-Sheet 2 Filed Dec. 23, 1958 FIG. 2

2,962,433 Patented Nov. 29, 1960 FUSED SALT ELECTROLYSIS CELL John D. Mueller and J. D. Russell, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware Filed Dec. 23, 1958, Ser. No. 782,540

2 Claims. (Cl. 204-247) This invention relates to an improved fused salt electrolysis cell. More particularly, it relates to an improved fused salt electrolysis cell having an improved type of electrode construction which provides increased current efliciency and other advantages.

Metallic sodium is generally obtained from the electrolysis of a composition of chloride salts including sodium chloride. The electrolysis has been long since carried out in cells of the Downs type (US. Patent 1,501,756). This cell is characterized by a centrally positioned bottom mounted vertically aligned graphite anode and a surrounding steel cathode of cylindrical shape having a slightly larger diameter than the said graphite anode. These electrodes, thus substantially concentrically mounted, define a narrow annular space within which electrolysis occurs. A cylindrical foraminous diaphragm is also usually concentrically positioned within the electrolysis zone, defined by said annular space, for the purpose of reducing the amount of recombination of the metallic sodium and chlorine after separation at the anode and cathode, respectively.

During recent years 'a new type of cell, basically similar to the Downs type, has emerged. This new cell employs a plurality of bottom mounted vertically aligned graphite anodes which extend upwardly into a cathode assembly having individual apertures or openings, the sides of which surround each of the said anodes in concentric fashion to form individual annular electrolysis zones. As in the original Downs cell, foraminous metal diaphragms are generally placed within each of the said annular electrolysis zones.

Both of these types of fused salt electrolysis cells have, in general, given good results. One disadvantage they possess, however, is that their current efficiency has been relatively low. Generally, the current efiiciency of the average multiple electrode cell of the Downs type ranges between about 83 to 86 percent. In commercial establishments improvement of current efiiciency is extremely important. Improvements on the order of only one percent can result in savings of many thousands of dollars in a fair size commercial establishment. The problems encountered in making any such improvements, however, are very numerous, difliicult and complex. Many approaches have been tried, most of them unsuccessful. But because of the importance of making those improvements, a great expenditure of money and effort has been spent in order to increase current efliciency. Various avenues have been investigated to determine how this could be done. For example, certain cell bath compositions have been experimented with so that current efiiciency may be increased in this manner. (See recently issued US. Patent 2,850,442.) One of the many factors which has been investigated extensively because of the serious adverse effects on current efliciency is that of calcium bridging. Precipitated calcium tends to form short circuits between the diaphragms and the cathodes, decreasing greatly the cell efliciency.

In view of this problem it is an object of this invention to provide an improved fused salt electrolysis cell for the production of metallic sodium, particularly an improved fused salt electrolysis cell wherein the current efliciency is greatly improved over other cells of this type. It is also an object of this invention to provide a cell wherein the durability of the diaphragms are greatly improved. Yet another object is to provide a cell wherein production of sodium and chlorine is increased. Other objects will appear hereinafter.

The apparatus of the invention will be fully understood from the description hereinafter and from the figures illustrating the preferred embodiment, wherein: Figure 1 is a sectional elevation view of an embodiment of the invention which is a multiple electrode fused salt electrolysis cell employing an embodiment of the invention, i.e. one having an eccentric anode-cathode type of construction. Figure 2 is a cross-sectional plan view taken along line 11 of Figure 1 showing the embodiment of Figure 1 in greater detail.

Broadly, the invention is a new and improved fused salt electrolysis cell of the multiple anode-cathode member type wherein the anodes, as well as the cathode members, conform to a symmetrical plan usually at about the center of the cell, but wherein the sum total effect is that the anodes and cathode members are offset from each other in eccentric fashion. Further, the eccentricity is such that between any given pair of anode-cathode members the distance between the centers of the openings within the cathode members is less than the distance between the corresponding anode centers. This will be more fully understood upon consideration of the following statements. Thus, there is provided a cell of the type wherein the cathode assembly has a plurality of cylindrical openings and a plurality of vertically aligned bottom mounted anodes having smaller cross-sectional diameters thanthe said cathode cylindrical openings, said anodes extending upwardly into the said cathode cylindrical openings but leaving spaces which are electrolysis zones having the cross-sectional configurations of eccentric annuli. Providing further, that in all embodiments the narrower sides of the said cross-sectional configurations are of greater radial distance from the cell center than the wider portions of the annular electrolysis zones.

Several embodiments are possible but in all cases the narrower side of'the eccentric annular shaped electrolysis zones will be generally or substantially away from the center of the cell. A preferred embodiment is one wherein the narrower sides of the eccentric annular shaped electrolysis zones are approximately percent of the dimensions of the sides having the greatest dimensions. Ranges of from about 85 to about percent are also generally satisfactory.

The principle of the invention and the embodiments thereof will be fully understood from the following detailed description.

Figure l is asectional elevation view of the cell according to its preferred embodiment. The plan disposition of the cell elements is more readily seen in Figure 2 which shows a cross-sectional plan view, taken along line 11 of Figure 1. Referring to Figure 1 and Figure 2 it is seen that the wall of the cell includes an exterior cell shell of steel plate 7, and a lining of refractory material 8. Centrally arranged, at the corners of a square in the cell are four cylindrical graphite anodes 9 9 9 9 A cathode assembly 15 includes four generally cylindrical portions 16 16 16 and 16 surrounding the individual anodes 9 and forming therewith the eccentric annular electrolysis zones 17 17 17 17 into which the diaphragms (represented in Fig. 1 by broken lines) are extended. The cylindrical portions 16 16 16 16 of the cathode assembly 15 are joined together by tangential connections and by webs. Electrodes 26 26 extend from the cathode assembly 15 and project through the openings 30 30 of the cell wall. The said openings are filled with a castable refractory material 31 31 The current is fed to the anodes 9 by the anode bus bars 2 2 through electrical connections not shown. A dome and collector assembly is mounted centrally above the anode-cathode electrodes and includes a chlorine dome 3 in the form of an inverted generally conical member and a sodium collecting conduit 1?. The chlorine dome terminates in a chlorine discharge line 5 the purpose of which is to transfer the gaseous chlorine to subsequent operations. The sodium collecting conduit 19 meets and is connected to a riser pipe 6.

The following working example is illustrative of a preferred mode of operating the invention.

In operation, the cell contains, up to a level approxi mately intermediate the full vertical elevation of the chlorine dome 3, fused electrolyte chlorides which are referred to as a bath. This molten bath includes not only sodium chloride but appreciable quantities of cal cium chloride. The sodium and chlorine are released in the eccentric annular spaces between the anodes 9 and cathode members 16 and rise on opposite sides of the diaphragm. The sodium collects within the sodium collecting conduit 19 and the chlorine gas is evolved through the chlorine dome 3 and discharge line 5.

Operation was continued in this manner for a period of 100 days. At the beginning of this period the cell operated at a current efiiciency of 93 percent and at the end of this time at a current efliciency of 87 percent. The overall average current efficiency, or mean current efficiency, was 90 percent. This compares with an average current efliciency of generally about 86 percent for the ordinary cell having concentric anode-cathode members. Also an average greater overall production of metallic sodium, and chlorine, was produced. Production was greatly increased as contrasted with the production obtained in ordinary cells having concentric anode-cathode members. It was also found that the operational life, or durability, of the diaphragms was considerably increased. Thus, the new and improved cell according to the present invention provides definite advantages over fused salt electrolysis cells built with concentric anode-cathode members.

Having thus described the invention and its best mode of operation, it will be realized that some variation of the specific design of the cell is permissible, subject to the limitation that the electrolysis zones formed between the anode-cathode members have the cross-sectional configurations of eccentric annuli wherein the narrower sides of the said configurations are at substantially greater distances from the center of the cell than other portions of the said annuli. Of course it will be realized that a cell can be constructed wherein the cathode cylindrical openings or apertures can be offset in preference to the anodes and the same result, as taught in the foregoing specification, obtained. Generally, the dimensions of the narrower side of the eccentric annuli should be approximately 90 percent of the widest sides of the said electrol ysis zones or eccentric annuli.

Having fully described the apparatus what is claimed is:

1. An improved cell of the multiple electrode type for the electrolysis of fused salts, said cell comprising a unitary cathode structure having a plurality of cylindrical apertures, said apertures having centers substantially equidistant from. the center of the cell and also conforming to a symmetrical plan about a line which is substantially through the center of the cell and which bisects a line through the centers of a pair of the cylindrical apertures, and a corresponding number of vertically aligned, bottom mounted anodes having smaller cross sectional diameters than the said cathode cylindrical apertures and projecting upwardly into the said cathode cylindrical apertures and thereby forming annular electrolysis zones, the anode centers being positioned on a symmetrical plan which corresponds to and parallels but is larger than the cathode plan, said electrolysis zones defining eccentric annuli, the wider and narrower portions thereof being located substantially radially from the center of the cell, and the wider portions of the said eccentric annuli being located closer to the center of the cathode structure plan than the narrower portions and the dimensions of the narrower sides of the electrolysis zones being from about to about 95 percent of the dimensions of the wider sides of the said electrolysis zones.

2. The apparatus of claim 1 wherein the dimensions of the narrower portions of the electrolysis zones are about percent of the dimensions of the wider portions of the electrolysis zones.

References Cited in the file of this patent UNITED STATES PATENTS 2,648,631 Carlisle Aug. 11, 1953 2,887,448 Bergy et a1. May 19, 1959 2,893,940 Smith July 7, 1959

Claims (1)

1. AN IMPROVED CELL OF THE MULTIPLE ELECTRODE TYPE FOR THE ELECTROLYSIS OF FUSED SALTS, SAID CELL COMPRISING A UNITARY CATHODE STRUCTURE HAVING A PLURALITY OF CYLINDRICAL APERTURES, SAID APERTURES HAVING CENTERS SUBSTANTIALLY EQUIDISTANT FROM THE CENTER OF THE CELL AND ALSO CONFORMING TO A SYMMETRICAL PLAN ABOUT A LINE WHICH IS SUBSTANTIALLY THROUGH THE CENTER OF THE CELL AND WHICH BISECTS A LINE THROUGH THE CENTERS OF A PAIR OF THE CYLINDRICAL APERTURES, AND A CORRESPONDING NUMBER OF VERTICALLY ALIGNED, BOTTOM MOUNTED ANODES HAVING SMALLER CROSS SECTIONAL DIAMETERS THAN THE SAID CATHODE CYLINDRICAL APERTURES AND PROJECTING UPWARDLY INTO THE SAID CATHODE CYLINDRICAL APERTURES AND THEREBY FORMING ANNULAR ELECTROLYSIS ZONES, THE ANODE CENTERS BEING POSITIONED ON A SYMMETRICAL PLAN WHICH CORRESPONDS TO AND PARALLELS BUT IS LARGER THAN THE CATHODE PLAN, SAID ELECTROLYSIS ZONES DEFINING ECCENTRIC ANNULI, THE WIDER AND NARROWER PORTIONS THEREOF BEING LOCATED SUBSTANTIALLY RADIALLY FROM THE CENTER OF THE CELL, AND THE WIDER PORTIONS OF THE SAID ACCENTRIC ANNULI BEING LOCATED CLOSER TO THE CENTER OF THE CATHODE STRUCTURE PLAN THAN THE NARROWER PORTIONS AND THE DIMENSIONS OF THE NARROWER SIDES OF THE ELECTROLYSIS ZONES BEING FROM ABOUT 85 TO ABOUT 95 PERCENT OF THE DIMENSIONS OF THE WIDER SIDES OF THE SAID ELECTROLYSIS ZONES.

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