United States Patent (19) WI NNNM

United States Patent (19) (11) 4,089,770 Lemke 45) May 16, 1978 54 ELECTROLYTIC CELL (56) References Cited U.S. PATENT DOCUMENTS 75 Inventor: Charles H. Lemke, Newark, Del. 2,041,821 6/1946 Gardiner . ... 204/247 3,607,684 9/1971 Kuhn ...... 204/68 X 73 Assignee: E. I. Du Pont de Nemours and 3,962,064 6/1976 Brut et al. 204/68 X Company, Wilmington, Del. Primary Examiner-John H. Mack Assistant Examiner-D. R. Valentine 21 Appl. No.: 814,432 57 ABSTRACT An electrolytic cell for the electrochemical separation of selected metals from electrodissociatable compounds 22 Filed: Jul. 11, 1977 thereof in the molten state utilizing as electrode separa tor a plurality of solid electrolyte tubes which, under 51) Int, C. ........................... C25C3/08; C25C3/02 the influence of an electrical potential, are permeable to 52 U.S. Cl. ...................................... 204/247; 204/68; the flow of selected cations, but impermeable to fluids 204/237; 204/245 and the flow of anions and other cations. 58) Field of Search ................................ 204/245-247, 204/237, 68,243-244 24 Claims, 2 Drawing Figures 33 K WI SaaaaaaavNNNM NSSR V YYYYYYYYas 7OO 2 'Z2 YZZ U.S. Patent May 16, 1978 Sheet 2 of 2 4,089,770 zzzzzzzzzzzzzzzzz-z-z-z-z-z-z-z-z-z-z-z-z-z-z, | N ?)==============================K–?) ========================| ANS 4,089,770 1. 2 tion, the heat produced by the operation of a battery of ELECTROLYTC CELL such electrolytic cells coupled with the necessity of conducting the operation in a closed building present BACKGROUND OF THE INVENTION problems of heat discomfort for operating personnel The invention is directed to an improved electrolytic 5 despite the use of extensive ventilation facilities. The cell for the separation of metals from electrodissociata waste heatrequiring such extensive ventilation is gener ble compounds in the molten state. It is particularly ated by the passage of direct current through the cells useful for the separation of alkali metals. and represents a large energy loss in addition to the The metals most frequently made by electrolysis of energy required for the operation of the ventilation electrodissociatable compounds in the molten state are 10 system. the alkali metals, particularly sodium and lithium. Therefore, from the standpoints of energy consump A considerable proportion of the elemental alkali tion, product quality and the comfort of operating per metals which are manufactured for commerce is pro sonnel, it is immensely desirable to have an electrolytic duced by the electrolysis of molten halogen salts of the process and cell which is operable at substantially lower metals, especially low melting mixtures of such salts 15 temperatures at the same or higher efficiencies. with other salts which are inert. For example, sodium A most promising route by which these disadvan metal can be produced by electrolysis of a molten bi tages of the prior art can be overcome is to employ an nary mixture comprising calcium chloride and sodium electrolytic process in which a solid electrolyte mate chloride or a ternary mixture such as sodium chloride, rial, which, under the influence of an electrical poten calcium chloride and barium chloride. On the other 20 tial, is permeable to the flow of selected cations, but hand, lithium metal is produced by electrolysis of a impermeable to the flow of other species, i.e., fluids, molten binary mixture comprising potassium chloride anions and other cations, to separate the anode and and lithium chloride. cathode compartments of the cell. A basic method for The type of electrolytic cell most widely used for the carrying out the electrowinning of alkali metals in this above-described operations is the Downs cell, which is 25 described in U.S. Pat. No. 1,501,756 to J. C. Downs. manner is disclosed in U.S. Pat. Nos. 3,404,036 and The Downs-type electrolytic cell basically is comprised 3,488,271 to Kummer et all in which a flat plate of so of a refractory-lined steel shell for holding the molten dium beta alumina is used as the solid electrolyte mate salt electrolyte, a submerged cylindrical graphite anode rial. A similar method is disclosed in U.S. Pat. No. surrounded by a cylindrical steel cathode and a perfo 30 3,607,684 to Kuhn in which sheets of beta alumina are rated steel diaphragm positioned in the annular space used as a diaphragm to separate the anode and cathode between the electrodes to separate the anode and cath compartments of the electrolytic cell. ode products. To collect product halogen gas from the Though the cells of the prior art, which have em anode, the cell is provided with collector means such as ployed solid electrolyte material as a separator between an inverted cone which fits over the anode below the 35 the cathode and anode, are effective in carrying out the surface of the molten bath. Halogen gas (usually chlo electrolytic separation of metals from molten salts rine) passes upwardly through the cone and, via appro thereof, such cells have remained largely undeveloped priate manifold components, from the cell. Similarly, and lack the configuration necessary to obtain efficient the cathode is also provided with collector means such continuous operation on a commerical basis. In particu as an inverted inclined trough which fits over the cath lar, the cells of the prior art have not been of such de ode below the surface of the molten bath. Molten alkali sign as to provide for safe continuous cell operation in metal rises from the cathode toward the surface of the the event of breakage of the fragile solid electrolyte molten bath, is collected along the inclined surface of material, nor do such prior art cells permit efficient use the trough and is passed to a vertical riser/cooler in of electrical energy and factory floor space by provid which the molten metal is partially cooled before it is 45 ing an acceptable ratio of solid electrolyte surface area passed to a product receiver. to cell volume. Despite the current technical and economic superior ity of the Downs cell for making alkali metals, particu BRIEF DESCRIPTION OF THE INVENTON larly sodium and lithium, the cell nevertheless has sev In view of the shortcomings of the electrolytic cells eral disadvantages which are becoming even more 50 in the prior art, the invention is directed to a cell for the highly significant as additional emphasis is placed on electrochemical separation of selected metals from elec energy conservation and the quality of working envi trodissociatable compounds thereof in the molten state ronment for operating personnel. comprising For example, in the manufacture of sodium, it is nec (a) an enclosed shell having top, bottom and side essary to use a molten salt bath temperature of about 55 members; 500-600 C in order to maintain the electrolyte compo (b) a molten metal collection zone comprising nents in the molten state. At this temperature (high with (1) an upper horizontal fluid-tight partition positioned respect to the melting point of sodium) significant below the top of the cell, the partition having a amounts of electrolyte salts and alkaline earth metals plurality of open risers extending above the upper dissolve in the product sodium and tend to plug the cell 60 surface of the partition, the riser tubes being in fluid riser/cooler. Thus, for reasons of product purity as well communication with as safety of operating personnel, the riser/coolers of (2) a plurality of corresponding solid electrolyte tubes Downs cells are equipped with an agitation device of suspended from the upper partition, the tubes being “tickler' by which the salts and extraneous metals joined to the upper partition in fluid-tight relation which are precipitated therein can be prevented from 65 ship at the upper end and closed at the lower end, plugging the riser pipe. Such devices are well known in and the art and are described inter alia in U.S. Pat. Nos. (3) outlet means for removing molten metal in the 2,770,364, 2,770,592, 3,037,927 and 3,463,721. In addi collection zone from the cell; and - 4,089,770 3 4. (c) an electrolyte circulation zone beneath the upper materials useful as reaction zone separators (solid elec horizontal partition comprising trolyte) are the following: (1) a plurality of positive pole assemblies, each con 1. Standard beta-type alumina which exhibits the nected with positive current collector means, posi above-discussed crystalline structure O-11Ala series of tioned concentrically to the outer longitudinal sur 5 layers of aluminum oxide held apart by layers of linear face of each of the solid electrolyte tubes, Al-O bond chains with sodium occupying sites between (2) outlet means for removing gas from the electro the aforementioned layers and columns. Beta-type alu lyte circulation zone near the top thereof, and mina is formed from compositions comprising at least (3) inlet means for feeding electrolyte feed materials about 80% by weight, preferably at least about 85% by into the circulation zone. O weight of aluminum oxide and between about 5 and In a preferred aspect of the invention, each of the about 15 weight percent, preferably between about 8 solid electrolyte tubes contains inert solid material by and about 11 weight percent, of sodium oxide. There which the amount of molten metal in the tubes during are two well known crystalline forms of beta-type cell operation is reduced. alumina, both of which demonstrate the generic beta 15 type alumina crystalline structure discussed herein DETAILED DESCRIPTION OF THE before and both of which can easily be identified by INVENTION their own characteristic X-ray diffraction pattern.

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