US2913387A

US2913387A - Electrolysis cell

Info

Publication number: US2913387A
Application number: US668417A
Authority: US
Inventors: Herbert B Williams; Tesmar Charles H Von; Renner John
Original assignee: National Distillers and Chemical Corp
Current assignee: Millennium Petrochemicals Inc
Priority date: 1957-06-27
Filing date: 1957-06-27
Publication date: 1959-11-17
Anticipated expiration: 1976-11-17

Description

1959 H. B. WILLIAMS EI'AL 2,913,387-

ELECTROLYSIS cw.

Filed June 27, 1957 2 sheets-sheet 1 CATHODE CATHODE L R R L O A m m E Lm L L F E E G D I cAsm 6 l4 ANODE HERBERT B.WILLIAMS CHARLES H.v0n TESMAR JOHN RENNER INVENTOR. BY Zimwce XDM-MA ATTORN EY FIG.|

REFRACTORY CASING l5 SLOT 6 DIAPHAGM H. a. WILLIAMS L 2,913,387

Nov. 17, 1959 ELECTROLYSIS cm. k

2 Sheets-Sheet 2 Filed June 27, 1957 GATHODE HERBERT B.WILL|AMS CHARLES H.von TES JOHN RENNE INVENTOR. BY i wwq 210% ATTORNEY United States Patent ELECTROLYSIS CELL Herbert B. Williams, Rochester, N.Y., Charles H. von Tesmar, Ashtabula, Ohio, and John Renner, Warners, N.Y., assignors to National Distillers and (Zhernical Corporation, New York, N.Y., a corporation of Virginia Application June 27, 1957, Serial No. 668,417

'5 Claims. (Cl. 204247) This invention relates to new and improved electrolytic cells for fused salts. More particularly, the invention concerns an improvement in cathode construction for electrolysis cells, whereby the cathode is provided with at least one slot adapted to permit transfer, passage, and removal from the cell of the molten metal cathodic products substantially out of contact with reactive gaseous anodic products.

This application is a continuation-in-part of Serial No. 504,144, filed April 27, 1955, now abandoned.

When metals are produced by electrolysis of fused salts, the cells are designed such that there is a relatively short distance between the cathode and the anode. This critical distance is necessitated, to a large extent, by the fact that fused salts and mixtures of fused salts are relatively poor conductors of electric current as compared with, for example, aqueous solutions of electrolytes. Even under the most advantageous conditions, however, the current efiiciency is not entirely satisfactory. For instance, in a typical electrolytic cell wherein fused sodium chloride undergoes decomposition to produce metallic sodium, the average current efliciency obtained is about 80%. This efficiency can be substantially increased and other advantages realized by preventing the recombination of the cathodic products with the anodic products. In the electrolysis of fused sodium chloride, for example, a number of serious difliculties are caused by the chemical recombination of sodium and chlorine.

The ordinary electrolytic cell is constructed with a metallic diaphragm, usually made of metal gauze or mesh, and positioned between the electrodes. This diaphragm is intended to prevent recombination. However, its use requires that both the molten cathodic product, sodium, and the gaseous anodic product, chlorine, travel upwardly along the entire vertical length of the electrodes before these products pass out of the electrolytic zone. During this passage the electrolysis products are separated only by the diaphragm and, thus, there is considerable opportunity for recombination. In electrolytic cells of ordinary design, there is also a continual accumulation of metallic sodium and calcium on the cathode. This accumulated metal causes short circuits across the diaphragm and periodic replacements of the gauze diaphragm are necessary.

It is an object of the present invention to provide an electrolytic cell structure for the production of sodium and chlorine from fused sodium chloride in which current efiiciency is substantially improved. It is another object of the invention to provide a cell structure in which, after initial decomposition, chemical recombination of elemental sodium and chlorine is substantially avoided by rapid removal of the metallic sodium from the zone in which decomposition is effected. It is a further object of the invention to reduce operating temperatures of such an electrolytic cell. This is also eifected by reducing the amount of recombination.

According to this invention, an improved design for electrolytic cells for producingsodium and chlorine from til 2,913,387 Patented Nov. 17, 1959 proved design is embodied in a cathode having at least one circumferential slot at a critical location in the electrolysis zone, coupled with a deflector shield for retaining and guiding liquid cathodic product out of and away from the electrolysis zone.

The cell used can be any one of the conventional type used in the electrolysis of alkali metal salts and mixtures thereof with alkaline earth metal salts for the production of alkali metals, having an anode and cathode or plurality thereof. In accordance with the invention, the cathode is provided with at least one slotted portion. It is possible to provide a cathode with about three slotted. portions, but the use of a single slotted portion is a. particularly preferred feature of this invention. It hasbeen found, for example, that the cathode structure is considerably weakened when too many slotted portions are employed, whereas the use of only a single slotted portion obviates this structural weakness. This arrangement offers the further advantage of maintaining a relatively large, uninterrupted vertical cathode surface in uniformly close proximity to the anode which permits operation of the cell at a lower voltage. In addition, as the number of slots are increased the economic advantage is lessened due to the high cost of fabricating such an intricate structure. By carefully locating the single slotted portion on the cathode, sufficient amounts of the molten cathodic product are effectively removed from contact with the gaseous anodic products to avoid much of the recombination difficulties encountered in the prior art electrolysis cells. Thus, it has been found that when the cathode is provided with a slotted portion located about one third of the distance up from the lower end of the cathode, the cell voltage remains relatively constant over long periods of operation, while the total production of sodium from the cell is increased by amounts up to one percent. Diaphragm changes are also required much less frequently, and in actual operation the effective life of the diaphragm was doubled. When more than one slotted portion is employed, it is preferred that at least two of the slotted portions be located in the lower half of the cathode. Though it is preferred exception of contact with vertical stiffening or supporting bars, the slotted portions need not necessarily be continuously circumferential in a single plane. When more than one slotted portion is employed, they may be arranged as discontinuous, slotted portions which are vertically spaced, coaxial, and parallel to each other.

It is of particular importance in the construction of the slot itself that the slotted portion slopes upwardly and away from the anode. It has been determined in actual tests that the molten metallic sodium will thus flow upwardly through the slotted portion and to the outside of the cathode away from the anode. The slope should preferably be adjusted to the optimum angle for maximum cathode product removal which has been determined to be approximately about 50 to 60 from the horizontal.

It is a further feature of this invention that the top inner surface of the slotted portion is constructed to facilitate channeling of the sodium into the slotted opening. This result is most conveniently accomplished by having a protruding portion, such as a protruding lip, at the top or upper edge of the opening. For instance, a projection of approximately 1 1" to /2" in size functions quite satisfactorily in directing and channeling molten sodium into the slot and to the outside of the cathode. A similar effect can be accomplished by offsetting the upper or top slot edge in relation to the lower slot edge. For example, the upper portion of the cathode might possess slot.

Another very important and additional novel feature of the invention is the use of a metal deflector shield which causes the cathode product to flow up the cathode of the cathode to the collector without dilfusing through the bath, burning on the top of the cell or recombining with the anodic product. The deflector means are positioned between the cathode and the inner wall of the electrolysis cell in close proximity to the outside periphery of the cathode, so as to confine the sodium and direct it upwardly into the collector, suspended above. The defiector means may, for example, be attached to the arm which holds the cathode in position in the cell. Though the deflector means may extend the length of the cathode, it is only necessary that the deflector means extend to a point just below the lowest slot in the cathode to ensure the upward channeling of the cathodic product flowing through the slot.

The collecting means useful for the purposes of this invention may be any of the conventional types. It is preferred, however, that the collecting means be located annularly around the gaseous anodic product collecting dome and that it extend over the cathode assembly, including the deflector means. When a diaphragm is employed, it may conveniently be attached directly to the inner wall of the collecting means and suspended about mid-way in the annular space between the anode and the cathode. The diaphragm may be of the perforated, cylindrical steel type.

Numerous advantages result when the improved electrolysis cell of this invention is utilized. These advan tages are achieved principally because the construction substantially prevents direct contact between the molten cathode product and the gaseous anode product. More specifically, the inventive electrolytic cell effectively prevents contact between molten sodium and gaseous chlorine in the electrolysis of fused sodiumchloride. Thus, the principal advantage is the avoidance of chemical recombination between the anode and cathode products by removing rapidly, and as formed, a substantial portion of the cathode product from the area where recombination is most likely to occur. This materially increases the cfiiciency of the cell and also has the beneficial eilect of decreasing D e cell temperature which normally is increased by the heat of the recombination reaction.

Upward passage of a large portion of the cathode product along the outside of the cathode between the metal deflector and cathode, and its rapid removal from the cell also reduces the amount of products which diffuse through the diaphragm between the electrodes. period of usefulness of the diaphragm itself is, consequently, extended since there is less accumulation of materials between the cathode and the diaphragm thereby reducing the number or" short circuits. This is particularly true for electrolytic cells wherein fused mixtures of sodium and calcium salts are used as the electrolyte. At the temperatures used in'the process some calcium metal is obtained as a by-product, and a portion of the calcium would ordinarily deposit on the metal diaphragm and form bridges which cause current losses and short circuits. Such short circuits substantially reduce the power efllciency of the cell and cause localized overheating of portions of the diaphragm, materially shortening its useful life.

One method and type of apparatus for carrying out the invention is illustrated by the appended drawings. Figure l is a diagrammatic vertical sectional view of an electrolysis cell containing the cathode assembly of this invention. Figure 2 is a horizontal cross sectional view taken on the plane y-y of Figure 1, while Figure 3 is an enlarged view of a small section of the cathode and deflector assembly and shows the slotted portion in greater detail.

Referring now to Fig. 1, there is shown a cylindrical electrolysis cell having an iron or steel cylindrical cell wall lined with refractory material 13, a cylindrical graphite anode 5 projecting upwardly through ceramic The.

4 casing 14 from the bottom of the cell, and a steel cylindrical cathode 3 positioned vertically coaxial with anode 5 and spaced apart therefrom. Cathode 3 has two diametrically opposed steel arms 4, which project outside of the cell, through ceramic insulating casing 15, to serve as electrode terminals. The cell is also provided with a perforated cylindrical steel diaphragm 8 attached to collector 9 and suspended in the annular space between anode 5 and cathode 3. The annular collector ring 9 serves to support diaphragm 8 and to collect molten metal which rises in the fused electrolyte from cathode 3. Outlet pipe 12 serves to carry the molten metal accumulated in collector ring 9 away from the cell, while gas dome 11 serves to carry away the gaseous anodic product formed by electrolysis. Deflector shield 1 is a solid, continuous metallic casing surrounding the cathode assembly, its principal function being to prevent dispersion throughout the cell of globules of molten metal by guiding the molten metal upwardly into collector 9 and out of the cell. The metal deflector l is supported by cathode arms 4 and is positioned in the annular space between refractory material l3 and cathode 3. Anode 5 and cathode arms 4 are insulated from direct contact with cell wall 10 by refractory

ceramic casings

14 and 15, respectively.

Cathode 3 is provided with a slotted portion 6, which is a circumferential opening located in the lower third of cathode 3. The slot is sloped upwardly and away from the anode 5. The upper edge of slotted portion 6 is provided with a protruding lip 7, extending around the entire inner wall of cathode 3. In Figure 2 the protruding lip 7 is shown in relationship with other members of the electrolysis cell of this invention, while in Figure 3 the slotted portion and the protruding lip are shown in greater detail in relationship to cathode 3 and deflector 1. In a typical operation of the cell shown in Fig. 1, a mixture of about 42 weight percent sodium chloride and 58 weight percent calcium chloride is placed in the brick lined cell provided with the above described upwardly projecting anode 5, slotted cathode 3, deflector shield 1 and a steel gauze diaphragm 8. Current is applied to the electrodes with an average voltage of about 6 to 7 volts depending on the amperage, which in turn is variable depending on the production level desired. The temperature is approximately 600 C. which maintains the fused salt mixture in a molten state. As the sodium chloride is electrolyzed, the chlorine collects at the anode and is passed upwardly and out of the cell via gas dome 11. The principal portion of the molten sodium formed during electrolysis collects on the lower part of cathode 3 on the inner side adjacent to anode 5. As the molten sodium starts to move upwardly, its flow is interrupted by protruding lip 7, which channels substantially all of the molten sodium formed below the slotted portion through slot 6 to the outside of cathode 3. The molten sodium is then directed upwardly through the annular space formed by metal deflector 1 and the outside of cathode 3 into collector ring 9 and out of the cell via outlet pipe 12. Experience has shown that the greater portion of the electrolysis products are formed in the lower third of the electrolytic zone, since a greater proportion of the current flows through the lower resistance path. Thus, a considerable amount of the molten sodium formed during electrolysis is passed out of the cell substantially out of contact with the chlorine gas thereby preventing the anodic and cathodic products from recombining.

While the principles of the invention have been described above with respect to one particular form of electrolysis cell, it will be understood that equivalent forms of apparatus are also contemplated. Thus, cells embodying the slotted cathode may be constructed with a plurality of anodes each individually circumscribed by the inventive cathode assembly. It will be appreciated that the use of such cells will call for modifications which l be within th p r e o hose k d n thread- One variance might involve the use of only one deflector shield surrounding the bank of anodes and cathodes. Such an arrangement would utilize in part the outside walls of the adjacent cathodes as means for directing a portion of the flow of the molten cathodic product, after its passage through the slots, upwardly into the collector and out of contact with the gaseous anodic products. It will be understood, therefore, that other modifications and variations may be employed within the scope of the invention described above and the following claims.

What is claimed is:

1. A cell adapted for electrolysis of fused salts having a cylindrical vertical side Wall, at least one vertically disposed anode extending upwardly from the bottom of said cell, a cylindrical, concentric cathode spaced apart from and surrounding said anode, collecting means positioned above said cathode and adapted to collect cathodic product, said cathode being provided with from one to three vertically spaced, coaxial, parallel and substantially circumferential slots, each of said slots sloping upwardly away from said anode and having a protruding portion at the upward edge of said slots on the inner wall of said cathode, said protruding portion being adapted to channel cathodic product from below said slots through said slots and out of contact with anodic product, the remainder of said cathode being continuous, vertically disposed deflector means disposed between said cathode and inner Wall of said cell, said deflector means being spaced apart from said cathode and said inner wall and adapted to channel cathodic product exiting from said slots upwardly and into said collecting means.

2. A cell according to claim 1 wherein said cathode is provided with one slot, said slot being located in the lower portion of said cathode.

3. A cell according to claim 2 wherein said slot is located about one-third from the bottom of said cathode.

4. A cell according to claim 1 having a vertically disposed diaphragm between said cathode and said anode, said diaphragm being spaced apart from said cathode and said anode.

5. A cell according to claim 1 wherein said slots are sloped at an angle from about to from the horizontal.

References Cited in the file of this patent UNITED STATES PATENTS 1,921,376 Ward Aug. 8, 1933 1,921,377 Ward Aug. 8, 1933 2,592,483 Smith et a1. Apr. 8, 1952

Claims

1. A CELL ADAPTED FOR ELECTROLYSIS OF FUSED SALTS HAVING A CYLINDRICAL VERTICAL SIDE WALL, AT LEAST ONE VERTICALLY DISPOSED ANODE EXTENDING UPWARDLY FROM THE BOTTOM OF SAID CELL, A CYLINDRICAL, CONCENTRIC CATHODE SPACED APART FROM THE SURROUNDDING SAID ANODE, COLLECTING MEANS POSITIONED ABOVE SAID CATHODE AND ADAPTED TO COLLECT CATHODIC PRODUCT, SAID CATHODE BEING PROVIDED WITH FROM ONE TO THREE VERTICALLY SPACED, COAXIAL, PARALLEL AND SUBSTANTIALLY CIRCUMFERENTIAL SLOTS, EACH OF SAID SLOTS SLOPING UPWARDLY AWAY FROM SAID ANODE AND HAVING A PROTUDING PORTION AT THE UPWARD EDGE OF SAID SLOTS ON THE INNER WALL OF SAID CATHODE, SAID PROTUDING PORTION BEIN ADAPTED TO CHANNEL CATHODIC PRODUCT FROM BELOW SAID SLOTS THROUGH SAID SLOTS AND OUT TO CONTACT WITH ANODIC PRODUCT, THE REMAINDER OF SAID CATHODE BEING CONTINUOUS, VERTICALLY DISPOSED DEFLECTOR MEANS DISPOSED BETWEEN SAID CATHODE AND INNER WALL OF SAID CELL, SAID DEFLECTOR MEANS BEING SPACED APART FROM SAID CATHODE AND SAID INNER WALL AND ADAPTED TO CHANNEL CHTHODIC PRODUCT EXITING FROM SAID SLOTS UPWARDLY AND INTO SAID COLLECTING MEANS.