US2865833A - Electrolytic cell - Google Patents

Description

Dec. 23, 1958 J. RENNER ETAL 2,865,833

ELECTROLYTIC cm.

Filed July 24, 1956 2 Sheets-Sheet 1 JOHN RENNER CHARLES H. vonTESMAR HERBERT B.WILLIAMS INVENTOR.

Dec. 23, 1958 J. RENNER ET AL 2,865,833

ELECTROLYTIC CELL Filed July 24, 1956 2 Sheets-Sheet 2 43 43 y 44 I a o 44 i B i B Ii [[1 43 43 [I j FIG. 2

JOHN RENNER CHARLES H.von TESMAR HERBERT B.WILLIAMS INVENTOR.

BY 4x10 ELECTROLYTIC CELL John Renner, Warners, N. Y., Charles H. Von Tesmar,

Ashtabula, Ohio, and Herbert Baldwin Williams, Rochester, N. Y., assignors to National Distillers and Chemical Corporation, New York, N. Y., a corporation of Virginia Application July 24, 1956, Serial No. 599,821

4 Claims. (Cl. 204-245) The present invention relates to electrolytic cells for fused salt electrolysis and, for example, to cells for electrolysis of a molten alkali metal salt to produce an alkali metal. More particularly, the invention relates to an improved electrolytic cell adapted for electrolysis of a molten salt electrolyte to produce an alkali metal as, for example,.for production of sodium from a molten salt electrolyte containing sodium chloride.

Those skilled in the art are aware of numerous disclosures pertaining to electrolytic cells of various types adapted for fused salt electrolysis of molten salts and, for illustrative purposes, a cell for such a purpose is disclosed in U. S. Patent No. 2,592,483. By use of such a cell, the chemical compound or compounds to be electrolyzed are maintained as a liquid bath in the cell in which an anode and cathode, or a plurality thereof, are disposed in suitable manner whereby the desired decomposition is eifected by electrolytic means. A specific illustration relates to decomposition of sodium chloride into sodium and chlorine by maintaining, in a vessel containing a suitable electrolytic cell, a molten bath containing sodium chloride at an elevated temperature (e. g., about 550 to 650 C.) with operation of the cell at a voltage of about 6 to about 7 volts, depending on amperage.

In cells normally used for such a purpose, the electrodes are separated by a narrow annular space as fused salts are relatively poor conductors,'particularly when compared with aqueous solutions of electrolytes, so as to avoid undue power consumption per pound of metal obtained. Moreover, in the production of 'a metal by electrolysis of a fused salt, it is generally necessary to use a mixture of a salt of the desired metal with one or more salts of another metal or metals in order to provide for the electrolysis an electrolyte having a suitable melting point. Thus, in the production of sodium by electrolysis of sodium chloride, a suitable substance such as calcium chloride is used in mixture with sodium chloride, the amount of thecalcium compound employed being con- [trolled so as to provide a mixture of suitable melting point and in which mixture the concentration of calcium is such that formation of an undesired separate phase of calcium is avoided or minimized during operation of the cell. For example, in a typical operation of a sodium cell, a suitable mixture for the electrolysis operation may consist of about 42 weight percent sodium chloride and 58 weight percent calcium chloride.

During operation of such cells and to keep the operating cell in balance, a considerable amount of heat energy must be dissipated continuously. For operation of conventional cells at relatively high amperages, such as up to about 38,000 amperes, the desired dissipation of heat can be effected by means such as cooling pipes and water jackets on the base of the cell and the cathode arms'to supplement the heat losses due to radiation and convection'and to provide some means of control over thecell temperature. However, when it is desired to operate-such cells at higher amperages, such as on the order f 40000 amperes or more, such means for dissipation of heat have proved inadequate and increasing the cooling capacity of such cooling means has not proved satisfactory for several reasons discussed more fully hereinafter.

In the operation of the electrolytic cells at relatively high amperages as well as at lower amperages, some cooling at the base of the cell is desirable, particularly so as to maintain the anode contacts at a relatively cool temperature. Similarly some cooling is required on. the cathode arms of the cell to maintain the cathode contacts at a relatively cool temperature, and to preserve the cathode neck seal. However, in instances wherein it is essential to dissipate more heat energy than is normally required for keeping the cell in thermal balance, i. e., at higher amperages than those for which the cell was originally designed, resort to more extensive cooling at the cell base has proved undesirable in that 1) the anode is subjected to thermal shock to the extent of cracking the anode, (2) undue freezing of the electrolyte at the bottom of the cell occurs which restricts circulation of the electrolyte and causes freezing of the gauze normally disposed between the narrowly spaced-apart electrodes with consequent restriction of flow through this electrolytic zone. It has also been found that the additional cooling required to control the cell at higher amperage operation, and to keep the cell in thermal balance cannot be supplied through the cathode arms since breakdownof the neck seal surrounding the cathode arm occurs which results in leakage of electrolyte from the cell. Such leakage of electrolyte causes a breakdown in the dielectric seal which lowers power eificiency of the cell, and also constitutes a physical hazard to personnel, necessitating pumpout of the cell. In addition, excessive cooling in this area causes undue freezing of the bath in the zone of the collector. This freezes the collector in place which causes considerable diflicultywhenever a diaphragmchange is required since the cell must then be heated up and heavily fiuxed with calcium chloride to melt out the bath and free the collector. Thisaddition of calcium chloride throws the bath composition out of balance, while the excessive heating disrupts the thermal balance, both of which result in a loss of power and production. Obviously, such difiiculties are more pro= nounced in the use at higher amperages of cells designed for lower amperage operation but are also encountered with cells designed for high amperage operation and in which the required amount of heat to be dissipated to maintain the cell in balance is effected by cooling means at the bottom portion of the cell. Hence, for the proper operation of cells, particularly those operated at relatively high amperages, there is a need to provide the cells with means to effect the desired dissipation of heat and maintain the cell in balance with minimization or elimination of difficulties as aforediscussed as well as other difliculties discussed hereinafter encountered by indiscriminate use of cooling means on portions of the cell other than at its base.

In accordance with this invention, there is provided an electrolytic cell adapted for fused salt electrolysis which contains means for base cooling of the cell as well as discriminantly disposed cooling means in the external portion of the vessel containing the cell and cell bath. Thus, in electrolytic cells adapted for fused salt electrolysis, such as forproduction of sodium from sodium chloride, the improved cell structure embodied herein comprises a vessel, innerlined with a refractory material, which con tains ,an electrolytic cell comprising an anode and cathode, means for cooling the bottom portion of said vessel and anode during operation of said cell, collector means for collecting products of the electrolysis of the fused bath during operation of said cell, and cooling means discrim- L inantly disposed with respect to the cathode, cell bottom portion and collecting means such that, when the cell is in operation, the cell operation may be carried out with minimization or elimination of difliculties such as aforediscussed. In particular, by use of a cell structure as embodied herein, the electrolytic operation can be carried out without freezing of the cell bath in the vicinity of the cell bottom which would restrict bathcirculation, freezing in the vicinity of the collecting means is prevented, thermal shock of the anode and potential leaking through refractory material in the vicinity of the cathode supports is obviated, and other advantages are obtained while at the same time maintaining the cell in balance. In a specific embodiment, the cell structure embodied herein comprises a cylindrically shaped vessel containing a centrally located vertical anode surrounded by an annular cathode supported by cathode arms suitably supported in side wall portions of the vessel, a base plate support for said anode and which base'plate has a socket to accommodate the bottom portion of the anode, means for cooling the bottom portion of the anode during operation of the cell, and cooling-means disposed on the external portion of the side walls of said vessel at an area thereof removed from the vessel bottom, the cathode arm supports and the collecting means.

In order to further describe the invention, reference is made to the accompanying drawings in which Figure 1 shows, partly in elevation and partly in vertical crosssection, one embodiment of the present invention. Figure 2 shows in elevation a lower portion of a vessel adapted to contain an electrolytic cell and suitable disposition of cooling elements on the external walls of the vessel; and Figure 3 is a plan view taken on line 13-43 of Figure 2, showing the embodiment of cooling means disposed on the external portion of the vessel.

In Figure 1, which shows the lower portion of a fused salt electrolysis cell, the cell is shown as of cylindrical shape having a centrally located graphite anode 1 surrounded by an annular steel cathode 2 which is supported by two cathode arms 3. The anode is supported by base plate 4 which is a circular steel plate horizontally disposed and has formed therein anode socket 5. The base plate 4 and anode socket 5 may be a single, integral casting or the socket and base plate may be separately formed and welded together. At its periphery, plate 4 is provided with an upstanding flange 10. Base plate 4 is supported by beams 25 and insulators 26 which insulate the base plate and anode from ground.

Anode 1 is centered in socket 5 and an annular refractory cement layer 12 surrounds the anode.

The side walls of the cells are formed by a cylindrical steel shell 11 which is open at both ends and is provided with two suitable openings to receive cathode arms 3. The diameter of shell 11 is less than the diameter of plate 4 so that when shell 11 is centered with the anode there is an annular space between the shell and flange 10. In constructing the cell, three or. four insulating refractory bricks 33 are placed on plate 4 to support the shell. Refractory insulating cement 12 is then placed in the annular space between shell 11 and the anode and in the annular space between shell 11 and the flange 10. The layer of refractory cement 12. is sufficiently thick to cover the top of the anode socket 5. After the refractory cement has set the shell 11 is lined with refractory brick 13 or other suitable refractory in conventional manner, and during this operation, cathode 2 is installed in the usual and conventional manner. In order to install the cathode with the arms 3 projecting through the sides of the cell, the shell 11 is formed in two halves which are fastened together by conventional means, e. g., flanges 18 and bolts 19 after the cathode has been set in place, thereby forming an upper half and a lower half of the cell. Cathode arms 3 are sealed by refractory insulating cement 20, held in place by flanges 21 or by other suitable means. The cell is completed by adding the remaining conventional elements such as those shown in the drawing as collector ring and dome support assembly 14, diaphragm 7 supported by the collector ring assembly, gas collecting dome 15 and riser pipe 16 which serves to lead molten alkali metal to the cell receiver, not shown. Anode bus bar 22 is fastened to the base of anode socket 5 by means of bolts 23; bus bars 24 are fastened to cathode arms 3 by means of bolts 30. For cooling the bottom portion of the anode and cell, suitable means such as water jacket 40 is provided, as shown, with conduit means 41 being adapted for introducing cooling means, such as water, into jacket 40 and conduit means 42 for withdrawal of cooling water from jacket 40. For cooling the cathode arm contacts, such cooling can be effected in conventional manner by introducing cooling water into a surface hollow section in the cast cathode arm through suitable conduit means for introduction of cooling water and withdrawal of efiiuent from the hollow section.

In such an embodiment, and in accordance with this invention, supplementary cooling means are provided in discriminate manner on the external portion of shell 11. For obtaining the advantages that result by practice of this invention, the cooling means are disposed in heatexchange relationship with shell 11 at a portion or portions thereof (a) not higher than the bottom portion of the collector means 14, (b) above the refractory 12 in the base of the cell and (c) removed from the area of the cathode arms 3 through shell 11. A suitable disposition of the supplementary cooling means is illustrated in the drawings wherein, in the lower half of shell 11 are disposed a plurality of cooling tubes 43 at a portion of the shell above refractory 12, below collector 14 and, as shown more clearly in Figure 2, removed from the openings in shell 11 that accommodate the cathode arms 3. The cooling tubes 43 are preferably welded to shell 11 and may be additionally supported by means such as stilfeners 44.

In Figure 2, there is shown in elevation, an embodiment of a lower portion of a cell, with shell 11, such as shown in Figure 1, with openings 45 to accommodate the cathode arms and cooling tubes 43 secured to the external portion of the vessel walls, the cooling tubes being shown supported by stitfeners 44. As shown, the cooling tubes are removed from the area of the openings for the cathode arms, are disposed above the bottom of the cell and, by being disposed in the lower half portion of the cell are below the collector means when the shell is the lower half of a cell such as in the embodiment of Figure 1. Figure 3, which is a plan view taken on line BB of Figure 2, also shows the particular disposition of the cooling tubes, particularly with respect to the openings for the cathode arms.

It has been found that by use of such discriminately disposed cooling means with respect to the collector means, cell bottom and cathode arms, to supplement controlled cooling of the bottom portion of the anode and cell bottoms, the following advantages have been obtained over and above indiscriminate cooling of the cell bath or by use of increased cooling at the cell bottom or cell cathode arm such as by cooling jacket 40, or cooling of the cathode arm socket.

. (1) The cooling of the anode and cell bottom, such as formerly provided by water jacket 40, only, can be controlled such that the anode may be cooled to a desired temperature without excessive cooling to the extent that the anode is subjected to thermal shock that cracks the anode.

(2) The bath in the bottom portion of the cell is not cooled to the extent that bath freeze-out occurs to result in gauze 7 freezing which restricts bath circulation in the narrow electrolytic zone between the anode and cathode.

(3) The bath in the area of the collector means is prevented from freezing in and around the collector which would prevent bath circulation and product removal via the collector.

(4) Thermal shock of the refractory in the vicinity of the cathode arm leads into the cell is minimized whereby bath and potential leakage in that area is prevented, such as would occur upon thermal shock of the refractory 20.

As will be apparent to those skilled in the art, the novel cell structure embodied herein contains provisions for both cooling the bottom portion (e. g., anode bottom) of the cell and supplementary cooling in discriminate manner whereby cells diificult to operate in balance and efficiency by means of bottom cooling alone or in conjunction with cathode arm cooling can be successfully operated. Thus, in operation of such cells, the cooling effected at the bottom portion is controlled to an extent suflicient to maintain the anode cool (e. g., 100 C.) but not to the point where, if all of the cooling were effected at the anode bottom, the anode would be subjected to thermal shock resulting in anode cracking which causes cell failure and necessitates pump-out of electrolyte with complete rebuilding of the cell. Supplementing such use of controlled base cooling, the cooling means, employed in discriminate disposition as aforedescribed, are also controlled as to cooling capacity in order to remove from the cell only that amount of heat which is required to maintain the cell in balance. This avoids the difliculties as aforediscussed which result from supplementary heat removal in indiscriminate manner from the cell.

Of extreme importance, over and above the difliculties that are encountered by use of cooling means solely in the bottom portion of the cell, and particularly such use in cells operating at high amperages (e. g., over 38,000 amperes), practice of this invention prevents the cell bath from leaking through the bottom refractory and corroding through the base plate to the water jacket which creates a hazard from fire and eruption of molten bath. Thermal shock breakdown of the refractory cement bottom seal is accelerated by the use of base cooling water jacket 40, since expansion and contraction of the refractory bottom causes a separation between the anode 1 and the refractory bottom 12. The resulting fissure or fissures permits the flow of highly corrosive electrolyte to the base plate. A similar breakdown of the refractory brick lining 33 has not been observed when sidewall cooling coils 43 are used.

Although, in the described embodiment, a single anode has been used for illustrative purposes, the invention may be practiced with cells containing a plurality of anodes set in a common cell base. Moreover, the horizontal cross-sectional shape of the cell may be rectangular, circular, or oval, as desired, using a base plate of corresponding shape. The distance between flange and shell 11 may be varied considerably, but that distance, in combination with the material selected as refractory seal to fill that space, must be such that flange 10 is electrically insulated from shell 11.

While there are above disclosed but a limited number 1 of embodiments of the invention herein presented, it is possible to produce still other embodiments without departing from the inventive concept herein disclosed, and it is desired therefore that only such limitations be imposed on the appended claims as are stated therein.

What is claimed is:

1. A fused salt electrolysis cell comprising a horizontally disposed metal base plate, an anode-receiving metal socket set in said plate and extending below the bottom side thereof, an anode set in said socket and extending upwardly into a zone of electrolysis, a metal cathode in said zone surrounding said anode, a refractory-lined metal shell having a smaller cross-section than that of said plate and surrounding said cathode, said cathode being supported in said zone by cathode supporting means extending through an opening in an intermediate portion of said metal shell, the lower edge of said shell being 6 spaced above the top of said plate, a refractory material covering said base plate and extending upward to completely surround and tightly embrace said anode at a height above said socket, base-cooling means adapted to cool the base of said cell and base portion of said anode While said cell is in operation, collector means disposed in an upper portion of said cell and adapted to collect products of electrolysis from a fused salt bath during operation of said cell, and supplementary cooling means adapted to contain a liquid heat-exchange medium disposed at an exterior portion of and in heatexchange relationship with said metal shell, said supplementary cooling means being disposed at a portion of said shell intermediate the cell bottom portion and cathode arm supports and adapted to maintain the cell in thermal balance such that cracking of the anode is minimized when the cell is operated at such high amperage that anode cracking is induced by use of said basecooling means for substantially providing the required cooling of said cell.

2. A fused salt electrolysis cell, as described in claim 1, wherein said supplementary cooling means comprises a plurality of cooling tubes in heat-exchange relationship with an exterior portion of said shell.

3. A fused salt electrolysis cell, comprising a circular, horizontally disposed metal base plate, an anode-receiving steel socket set in said plate and extending below the bottom side thereof, an anode set in said socket and extending upwardly into a zone of electrolysis, a metal cathode in said zone surrounding said anode, a cylindrical, refractory-lined metal shell having a diameter less than that of said plate and surrounding said cathode, said cathode being supported in said zone by a cathode supporting means extending through an opening in an intermediate portion of said metal shell and refractory sealed in said opening, the lower edge of said shell being spaced above the top of said plate, said plate having at its periphery an upstanding metal flange extending above the bottom of said shell, a refractory insulating seal in the annular space between said flange and the lower part of said shell, a refractory material covering said base plate and extending upward to completely surround and tightly embrace said anode at a height above said socket, base cooling means adapted to cool the base of said cell and bottom portion of said anode while said cell is in operation, collector means disposed in an upper portion of said cell and adapted to collect products of electrolysis from a fused salt bath during operation of said cell, supplementary cooling means adapted to contain a liquid heat-exchange medium disposed at an exterior portion of said shell in heat-exchange relationship therewith, said supplementary cooling means being disposed at a portion of said shell intermediate said cathode supporting means and the refractory in the base portion of the cell, said supplementary cooling means being adapted to maintain the cell in thermal balance such that cracking of the anode is minimized when the cell is operated at such high amperage that anode cracking is induced by use of said base-cooling means for substantially providing the required cooling of said cell and an electrical connection to said base plate.

4. A cell, as described in claim 3, wherein said supplementary cooling means comprises a plurality of cooling metal tubes secured in heat-exchange relationship to the metal shell.

References Cited in the file of this patent UNITED STATES PATENTS 663,719 Becker Dec. 11, 1900 1,913,145 Watt June 6, 1933 2,213,073 McNitt Aug. 27, 1940 2,592,483 Smith et a1. Apr. 18, 1952

Claims (1)

1. A FUSED SALT ELECTROLYSIS CELL COMPRISING A HORIZONTALLY DISPOSED METAL BASE PLATE, AN ANODE-RECEIVING METAL SOCKET SET IN SAID PLATE AND EXTENDING BELOW THE BOTTOM SIDE THEREOF, AN ANODE SET IN SAID SOCKET AND EXTENDING UPWARDLY INTO A ZONE OF ELECTROLYSIS, A METAL CATHODE IN SAID ZONE SURROUNDING SAID ANODE, A REFRACTORY-LINED METAL SHELL HAVING A SMALLER CROSS-SECTION THAN THAT OF SAID PLATE AND SURROUNDING SAID CATHODE, SAID CATHODE BEING SUOOORTED IN SAID ZONE BY CATHODE SUPPORTING MEANS EXTENDING THROUGH AN OPENING IN AN INTERMEDIATE PORTION OF SAID METAL SHELL, THE LOWER EDGE OF SAID SHELL BEING SPACED ABOVE THE TOP OF SAID PLATE, A REFRACTORY MATERIAL COVERING SAID BASE PLATE AND EXTENDING UPWARD TO COMPLETELY SURROUND AND TIGHTLY EMBRACE SAID ANODE AT A HEIGHT ABOVE SAID SOCKET, BASE-COOLING MEANS ADAPTED TO COOL THE BASE OF SAID CELL AND BASE PORTION OF SAID ANODE WHILE SAID CELL IS IN OPERATION, COLLECTOR MEANS DISPOSED IN AN UPPER PORTION OF SAID CELL AND ADAPTED TO COLLECT PRODUCTS OF ELECTROLYSIS FROM A FUSED SALT BATH DURING OPERATION OF SDASID CELL, AND SUPPLEMENTARY COOLING MEANS ADAPTED TO CONTAIN A LIQUID HEAT-EXCHANGE MEDIUM DISPOSED AT AN EXTERIOR PORTION OF AND IN HEATEXCHANGE RELATIONSHIPWITH SAID METAL SHELL, SAID SUPPLEMENTARY COOLING MEANS BEING DISPOSED AT A PORTION OF SAID SHELL INTERMEDIATE THE CELL BOTTOM PORTION AND CATHODE ARM SUPPORTS AND ADAPTED TO MAINTAIN THE CELL IN THERTMAL BALANCE SUCH THAT CRACKING OF THE ANODE IS MIMIMIZED WHEN THE CELL IS OPERATED AT SUCH HIGH AMPERAGE THAT ANODE CRACKING IS INDUCED BY USE OF SAID BASECOOLING MEANS FOR SUBSTANTIALLY PROVIDING THE REQUIRED COOLING OF SAID CELL.

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