US3497446A

US3497446A - Electrolytic cell with anodes secured to its cover

Info

Publication number: US3497446A
Application number: US368766A
Authority: US
Inventors: Thomas W Clapper; Ralph E Behrens
Original assignee: American Potash and Chemical Corp
Current assignee: American Potash and Chemical Corp
Priority date: 1964-05-20
Filing date: 1964-05-20
Publication date: 1970-02-24
Anticipated expiration: 1987-02-24

Description

Feb. 24, 1970 I w, CLAPPER ET AL 3,497,446

ELECTROLYTIC CELL WITH ANODES SECURED TO IT'S COVER Filed May 20, 1964 2 Sheets-Sheet 2 Tue/was w. GLAD/3E2 RALPH 5.. BEN/ZEUS INVENTORS BY Lee/5w ATTORNEY.

United States Patent 3,497,446 ELECTROLYTIC CELL WITH ANODES SECURED TO ITS COVER Thomas W. Clapper, Whittier, and Ralph E. Behrens, Monterey Park, Califi, assignors, by mesne assignments, to American Potash & Chemical Corporation, a corporation of Delaware Filed May 20, 1964, Ser. No. 368,766 Int. Cl. B01k 3/ 00; 02% 5/70 US. Cl. 204-242 5 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell having an electrically insulating cover and a plurailty of graphite anodes secured to the cover and extending into the cell. Each of the anodes is provided with an electrical connector secured internally thereof and terminating within the anode, the connectors being secured to the anodes by a electrically conductive metal alloy which has a negative coefiicient of expansion. Electrically conductive means are secured to each connector to electrically interconnect the anodes.

The present invention relates to electrolytic cells and has particular reference to improved electrolytic cells provided with novel internal contact graphite anodes.

The electrolytic cells of this invention are adapted particularly for the electrochemical conversion of aqueous sodium chloride to sodium chlorate as described in J. C. Schumachers US Patent No. 2,511,516. The cell will be described in connection with that process although it will be understood, of course, that its use is not so lim ited. Thus, for example, it also may be used in the manufacture of alkaline metal hypochlorites, chlorine and caustic.

It has been determined that, employing the cell of this invention, the said electrochemical process can be carried out in a continuous manner, with high efliciency, minimum danger from explosions and with certainty of control of the conditions of electrolysis within the cell for optimum production of sodium chlorate.

For a more complete understanding of the invention reference is made to the following description taken in conjunction with the accompanying drawing which illustrates, diagrammatically, in:

FIGURE 1, a top view of a part of an electrolytic cell in accordance with this invention, and in FIGURE 2, a cross-sectional view of the cell taken along the line 22 of FIG. 1.

Broadly, the electrolytic chlorate cell of this invention comprises a rectangular trough-like steel tank, the walls of which serve as electrolytic cathodes. The steel tank is adapted to contain the electrolyte which is circulated lengthwise through the cell.

The steel tank is provided with a relatively thick electrically insulating cover comprised of, for example, polyvinyl chloride. The cover is provided with a plurality of longitudinal slots through which vertically disposed graphite anodes extend into the cavity of the tank and downwardly into the electrolyte. The graphite anodes are electrically inner-connected by means of unique internal contact, electrically conductive metal studs. The cover may comprise molded, extruded, laminated or the like plastic material. In addition to polyvinyl chloride, other materials which may be used include glass-reinforced polyesters, epoxies, natural rubber and the like.

Referring to the drawings, the electrolytic cell of this invention comprises a steel tank of welded construction and of elongated trough-like structure to provide space for a plurality of parallel rows of electrodes. The

upper edges of the cell walls are provided with flanges 12 which provide support and mounting means for an electrically insulating cover 14 comprised, for example, of polyvinyl chloride. A resilient gasket 16, of rubber, cell putty or the like, is disposed between flanges 12 and cover 14. A plurality of mounting screws 18 serve to removably secure cover 14 to the flanges 12 of the tank 10. A plurality of metal ribs 15 extend longitudinally of the tank 10 at the top thereof to provide additional support for cover 14.

Cover 14 is provided with a plurality of longitudinal slots through which a plurality of vertically disposed graphite anodes 20 pass. The anodes are constructed of dense graphite or graphitized carbon plates and are maintained in position with respect to cover 14 and tank 10 by means of a plurality of pins 22 which pass through suitably drilled holes in the upper ends of the andoes. Pins 22 may be made of polyvinyl chloride, glass, wood or the like material, the only requirements being that the material be non-conductive, strong enough to support the anodes and resistant to corrosive attack by the electrolyte. It will be understood, of course, that other nonconductive support members in the form of blocks, wedges, plates or the like may be used in place of cylindrical pins 22.

Unique internal electrical contact between groups of graphite anodes is effected utilizing a system including a plurality of electrically conductive metal studs or connectors 24, made of copper aluminum, silicon bronze or the like, suitably disposed in operative association with the anodes. More specifically, as illustrated on the drawing, holes are drilled into the end of each anode 20. An electrical connecting stud 24 is placed in each hole and irremovably cemented in place by a suitable metal alloy 26. There are a number of alloy compositions which have been found to be suitable. It has been determined that, in addition to being electrically conductive, the alloy should be relatively low melting, e.g., 50-300 C., for ease of handling and must have a negative coefiicient of expansion meaning, of course, that it expands on cooling. This latter feature is absolutely essential to the invention to insure a tight contact. It also has been determined that particularly desirable results are obtained using an alloy containing, for example, bismuth, antimony, indium or the like. An example of a satisfactory alloy is one containing about 53% bismuth, 32% lead 31 1a 15% tin. This particular composition alloy melts at To avoid corrosion at the graphite-alloy interface, a quantity of a sealant composition 28 is packed above the solidified alloy to completely fill the space between the connector 24 and the graphite anode. The sealant effectively prevents any gaseous or liquid corrosive attack at said graphite-alloy interface. Moreover, quantities of such sealant also are applied about the anode-cover joints at 28 to provide a tight seal of tank 10.

Electrical connection between studs 24 is effected through anode bus bar 30 secured to studs 24 by means of locking nuts 32. As illustrated on the drawing a plurality of anodes is connected to a suitable power source or succeeding electrolytic cell (neither shown) by means of an electrical bus lead 34.

Banks of steel cooling water tubes or pipes 36 are provided and disposed longitudinally between pairs of rows of graphite anodes 20. These tubes provide means for maintaining and controlling uniform temperatures throughout the space in which the electrolysis reactions take place. The tubes, as well as the walls of tank 10, constitute cathodes in the electrolytic cell of this invention. Electrical connection for the cathodes conveniently is made by a cathode bus bar 38 welded to the tank flange 12 along one side of the cell with suitably spaced connector bolts 39 provided therein. An electrical bus lead 34' connects the cathode bus bar 38 to the anode bus bar 30 of the next cell in line.

A settling space, not shown, is provided below the anodes and the cooling tubes for the accumulation of sediment resulting primarily from the disintegration of the graphite anodes. The space between the electrolyte surface and the bottom of cover plate 14 quickly fills with gases evolved during the electrochemical process. When the cell is used for the electrolysis of sodium chloride to form sodium chlorate or in other similar reactions, the gases evolved generally comprise hydrogen, oxygen, chlorine and sometimes carbon dioxide. Escape of these gases readily can occur through outlet pipe 42 provided in tank 10' at one end of the cell.

Electrolyte is introduced into the cell through inlet pipe 40 located in one end of cover 14. Excess electrolyte overflows and is removed from the cell through hole 42, located in the end wall at the opposite end of the cell.

The cell of this invention is adapted particularly for use in a continuous, recirculating process such as in US. Patent 2,511,516 in which the electrolyte enters at one end of the cell, passes in contact along a relatively long row of a plurality of electrodes where the electrolytic chemical transformation takes place and subsequently exits as eflluent from the opposite end of the cell. Once removed from the cell, the effluent may be chemically treated, or additions of other chemicals may be made, or portions of the product may be removed, or it may be recirculated in and out of other cells in order to again contact the electrodes and be subjected to further electrolysis.

The cell of this invention has certain important advantages over prior art structures. Thus, because of the unique cover construction coupled with the novel means for mounting and supporting the graphite anodes in association therewith, it now is possible to obtain much more complete graphite utilization than was possible heretofore. The present cell design permits lower operating costs because its use results in a marked reduction in graphite consumption, lower maintenance costs, less labor requirements and lower power consumption per ton of chlorate produced.

Moreover, the unique internal graphite anode electrical contact structure in this cell permits continued low voltage operation for the life of the graphite. Prior art cells, not having this feature, exhibited contact deterioration relatively early in their life as evidenced by continuously increasing cell voltage readings.

The unique cover construction and associated internal contact anodes of the cell of this invention also provides an important means for reducing anode stub losses. The stub of an anode is that portion which extends above the level of the electrolyte in the tank. Since the stub portion of the anode always is lost, it is important for economic cell operation that it be as short as possible. In certain prior art cells, almost four inches of the anode extends above the top of the electrolyte because of the electrical contact and cell mounting means there employed. In the cell of the present invention, this stub has been reduced to less than two inches.

If desired, the stub length can be reduced even further in accordance with a modified form of this invention. Thus, instead of pinning and sealing or cementing the anodes in the slots in the cover, it is only necessary to provide suitable openings or drill holes in the cover, pass studs 24 therethrough and screw the same into threaded holes provided in the ends of the anodes. This modification provides an anode-cover butt joint on the lower surface of the cover and materially reduces stub losses even further.

While the present invention has been described with respect to what is considered to be its preferred embodiment, it will be understood, of course, that certain changes, substitutions, and modifications may be made therein without departing from its true scope.

What is claimed is:

1. An electrolytic cell consisting essentially of an electrically conductive tank adapted to contain an electrolyte and provided with an electrically insulating cover, a plurality of graphite anodes secured to said cover and extending into the electrolyte in said tank, each of said anodes having an electrical connector secured internally thereof and terminating within said anodes, said connectors being secured to said anodes by an electrically conductive metal alloy which expands on cooling, and electrically conductive means secured to said connectors to electrically interconnect said anodes.

2. An electrolytic cell as defined in claim 1 in which the end of each anode remote from the electrolyte is provided with a hole extending into and terminating within said anode, with at least one of said electrical connectors extending into said hole in each anode and being secured therein by said metal alloy.

3. An electrolytic cell as defined in claim 1 in which said metal alloy has a melting point within the range of from about 50 to about 300 C.

4. An electrolytic cell as defined in claim 1 in which a sealant is provided at the graphite anode-metal alloy interface, to prevent corrosion at said interface.

5. An electrolytic cell as defined in claim 1 in which said cover is provided with a pluralit of openings therein with said anodes extending through said openings into said cell, the end of each anode remote from the electrolyte extending above said cover, with each of said ends having a hole terminating within the anode and said electrical connectors extending thereinto and being secured therein by said metal alloy.

References Cited UNITED STATES PATENTS 3,023,393 2/1962 Oliver 204279 XR 667,498 2/1901 Chapman 204286 674,933 5/1901 Mauran 204288 728,274 5/1903 Moore 204-286 3,244,610 4/1966 Brown et al. 204279 JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner US. Cl. X.R. 204286, 297