US3707454A

US3707454A - Anode and base assembly for electrolytic cells

Info

Publication number: US3707454A
Application number: US157313A
Authority: US
Inventors: Richard E Loftfield; Henry W Laub
Original assignee: Diamond Shamrock Corp
Current assignee: Diamond Shamrock Chemicals Co; Eltech Systems Corp; Diamond Shamrock Corp
Priority date: 1968-09-27
Filing date: 1971-06-28
Publication date: 1972-12-26
Anticipated expiration: 1989-12-26
Also published as: DE1948803A1; BE739420A; CA959453A; FR2019046A1; LU59509A1; US3591483A; GB1227506A; DE1948803B2; NL138772B; NL6914670A

Abstract

AN ANODE AND CELL BASE ASSEMBLY IS PROVIDED WHICH FEATURES THE USE OF DEMENSIONALLY STABLE ANODES. IT IS CHARACTERIZED IN HAVING A CELL BASE WHICH SERVES AS A RIGID SUPPORT FOR THE ANODES, AS A CONDUCTOR FOR DISTRIBUTING CURRENT TO THE ANODES AND AS A RIGID SUPPORT FOR THE CELL CAN. FURTHERMORE A SHEET OF ELECTRICALLY NONDUCTIVE MATERIAL COVERS THE ENTIRE CELL BASE AND SERVES TO INSULATE THE CONTACT BETWEEN THE CELL CAN AND THE CELL BASE

AND ALSO PROVIDES A HYDRAULIC SEAL TO PREVENT LEAKAGE OF ELECTROLYTE.

Description

Doc. 26, 1972 LQF'TFIELD ET AL 3,707,454

ANODE AND BASE ASSEMBLY FOR ELECTROLYTIC CELLS Filed June 28, 1971 ,2 Sheets-Shoot '1 i i l l I l I I I 29 I V IIIIIIII V I "'-";IIIIIII'A"!4L'|IIIIIIIII RICHARD E. LOFTFIELD HENRY W LAUB ATTORNEY 26, 1972 n- ET AL 3,707,454

ANODE AND BASE ASSEMBLY FOR ELECTROLYTIC CELLS 2 Shanta-Shoat 2 Filed June 28, 1971 Fig. 4

E Fig. 5

31 I :P G

Fig. 6'

. INVENTORS RICHARD E. LOFTFIELD HENRY W LAUB ATTORNEY United States Patent O US. Cl. 204-242 5 Claims ABSTRACT OF THE DISCLOSURE An anode and cell base assembly is provided which features the use of dimensionally stable anodes. It is characterized in having a cell base which serves as a rigid support for the anodes, as a conductor for distributing current to the anodes and as a rigid support for the cell can. Furthermore a sheet of electrically nonductive material covers the entire cell base and serves to insulate the contact between the cell can and the cell base and also provides a hydraulic seal to prevent leakage of electrolyte.

REFERENCE TO A CO-PENDING APPLICATION This is a continuation-in-part of our co-pending U.S. Ser. No. 763,121 filed Sept. 27, 1968, now US. Patent No. 3,591,483.

BACKGROUND OF THE INVENTION Our Ser. No. 763,121 describes the combination of a metal base, an insulating sheet and dimensionally stable anodes for use in a diaphragm cell, the remaining components of which are essentially conventional. It has been found on further investigation that much of the teaching regarding use of such a combination in a diaphragm cell, applies as well to cells of the same general configuration, with regard to the cell can in which a diaphragm is not present, e.g., a chlorate or hypochlorite cell.

Many of the problems described in the previous application with regard to the diaphragm cell electrolysis of alkali metal halide solutions employing graphite anodes, have also plagued the producers of oxyhalogen compounds since the apparatus employed is often similar, only the diaphragm being absent.

STATEMENT OF THE INVENTION Therefore it is an object of the present invention to provide an anode and cell base assembly, useful with cell cans conventionally employed in the production of oxyhalogens by the electrolysis of alkali metal halide solutions.

This and further objects of the present invention will become apparent to those skilled in the art from the specification and claims which follow.

There has now been found, in a cell for the electrolysis of alkali metal halide solutions of the type comprising an anode and cell base assembly and employing a cell can, the improvement in the anode and cell base assembly which comprises:

(a) A conducting and supporting cell base means having holes disposed therein for the receipt of anode risers;

(b) A single sheet of at least one electrically non-conductive material covering the entire cell base, having holes disposed therein corresponding to the holes in the cell base and serving to provide compressible seals between the anodes and the cell base and between the cell can and the cell base and,

Patented Dec. 26, 1972 (c) Dimensionally stable anodes, said anodes comprising an electrically-conductive surface, a material supporting said conductive surface and an anode riser having a flange on the lower portion thereof and extending past said flange and through the cell base.

Such an assembly has extremely low resistance to the passage of current from bus bar to anode; may be assembled and disassembled rapidly and with good dimensional accuracy; may be operated at higher current densities, yields greater cell power, alkali metal halide conversion and current efiiciencies; allows fabrication of taller cells thereby conserving floor space, and Provides a relatively constant voltage over the entire life of the cell, all as opposed to cathodically similar electrolytic cells employing graphite anodes.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified end view of a typical anode and cell base assembly employing the improved construction and advantages of the present invention.

FIG. 2 is a simplified side view of a portion of a typical assembly according to the present invention.

FIG. 3 is a simplified view of a method of connecting an anode riser and cell base according to the invention and also shows the direct connection of a connecting condoctor to the aode riser used when the cell base is of a less conductive metal and does not serve as both a support and conducting means.

FIG. 4-6 represent anode configurations and designs which may be used according to the practice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It should be understood that the novelty of the instant invention does not reside in the design or configuration of the cell can. By cell can it is intended to refer to the portions of the cell other than the anode and cell base assembly, that is, the side walls, end walls and cover together with the cathode members which are attached to at least one of the walls or the cover and extend into the chamber defined by the walls and cover. Any of the cell cans currently in use are acceptable and may be adapted to the present invention provided that they may be deployed over the alternating array of anodes presented by the anode and cell base assembly of the invention. Typically, these cell cans employ electrically conductive side and end walls with cathode sheets, generally of iron or steel, traversing the chamber formed from sidewall to sidewall and in electrical connection therewith. It is understood that, in the absence of a diaphragm, there are no separate anolyte and catholyte compartments and therefore the products of electrolysis, e.g., chlorine and caustic, react within and/ or without the cell to produce the desired oxyhalogen compounds, e.g., sodium chlorate.

In essence the instant invention resides in (1) the cell base means, (2) the non-conducting sheet covering the cell base and (3) the dimensionally stalble anode and riser.

The conducting and supporting cel'l base means may be selected from one of two basic designs. In the first and preferred embodiment a unit construction will serve both as a supporting and electrical conducting means. In this embodiment the base will generally be constructed of a material selected from the group consisting of copper and aluminum, although steel and the like may be used in some instances, and will consist merely in a flat unit construction having disposed therein a number of holes through which the anode risers will extend. The outside electrical source (bus bar) will be connected directly to the cell base and current will fiow through the base to the anode risers. In a second embodiment the cell base means will be constructed of a somewhat less conductive material, such as iron or steel, which will serve mainly as a support for the cell. This less conductive material will again be in the form of a unit construction having holes disposed therein through which the anode risers will extend. However, in this instance a series of connecting conductors to which the individual anode risers may be connected, thereby providing direct distribution of the current to the anodes, completes the cell base means.

According to the simplified construction of the present invention there is provided over the entire surface of the cell base a thin, electrically nonconductive, sheet of material, preferably rubber. Titanium, which is generally nonconductive under conditions of cell operation may also be used if means for obtaining a compressible seal, such as O-rings and gaskets, are provided. This nonconductive sheet of material will also have holes disposed therein corresponding to the holes in the cell base for insertion therethrough of the anode risers. Generally, the holes will be slightly larger than the holes in the cell base in order to provide metal (riser) to metal (cell base) contact and afford good dimensional alignment. In the event that titanium constitutes the nonconductive layer, however, the hole need only be of the same dimension as the holes in the base. This nonconductive material is intended to serve as a seal to prevent the leakage of brine around the anode riser into the holes through which the anode risers extend. The nonconductive sheet of material also serves as a gasket to prevent leakage of brine between the cell base and the cell can and insulates the positively charged cell base from the negative cell can. In the instance where the nonconductive sheet is composed of rubber or a like material, the area which is in contact with the cell can may be provided with a ribbed surface which will act as a gasket to prevent leakage of brine from the cell. Alternately a ridge may be provided on the rubber surface which will compress somewhat under weight to provide a seal which is made more effective by the application of a small amount of chemically inert putty around the interior circumference of the cell. In the event that the nonconductive sheet is of a more rigid material such as titanium, it will be necessary to provide a gasket of rubber or the like material which will aid in preventing leakage of brine from the cell. Other designs will be obvious to those skilled in the art.

The dimensionally stable anodes which are useful in the practice of the present invention comprise an electrically-conductive surface, a material supporting said electrically-conductive surface and an anode riser in contact with the material which supports the electricallyconductive surface, said riser having a flange on the lower portion thereof and extending below said flange for such a distance as to project through the cell base. The electrically-conductive surface of the dimensionally stable anodes may be composed of any material which has a sufliciently low chlorine overvoltage and which is chemically inert to the electrolyte as well as resistant to the corrosive conditions of the cell. Typically this electricallyconductive surface will be composed of platinum group metals, alloys of platinum group metals, platinum group oxides, mixtures of platinum group oxides and alloys which are mixtures of platinum group metal oxides with platinum group metals. Also contemplated and especially preferred at this time are electrically-conductive surfaces which are mixtures of valve metal oxides with platinum group metals and platinum group metal oxides. For example, anode surfaces which are especially preferred at this time include platinum metal, platinum-palladium metal alloy platinum-iridium alloy, platinum oxide, ruthenium oxide, mixtures of platinum and ruthenium oxides, titanium oxide-ruthenium oxide alloys, titanium oxide-iridium-ruthenium oxide alloys, and the like. Again the invention is not dependent upon the particular nature of the electrically-conductive surface involved, it

being only important that it have an appropriately low chlorine overvoltage and good resistance to cell conditions.

The material which supports the electrically-conductive surface generally comprises a valve metal or an alloy thereof. By valve metal it is intended to refer to the filmforming metals such as titanium, tantalum, zirconium, niobium and the like. This material will preferably be in the form of a continuous sheet of metal but it may be perforated or foraminous in order to provide circulation of the anolyte. These valve metals have in common the property of being nonconductors themselves under the conditions of cell operation (an oxide of the valve metal quickly forms on the surface thereof thus preventing passage of current), but being able to conduct current when an electrically-conductive material is in contact with a portion of the surface thereof.

The material which supports the electrically-conductive surface is in contact with, generally by welding, the anode riser. This riser serves to dispose the anode in the proper manner within the cell and to convey electrical current to the anode surface. The riser is preferably constructed, at least on the outer portions thereof, of a valve metal such as titanium or tantalum. As an alternative to using a riser consisting of a solid valve metal, it is possible to use a copper, sodium or aluminum-cored riser having a layer of a valve metal on the outside. This is preferable both due to the lower cost of the copper, sodium or aluminum and because such metals are inherently better conductors of electricity than are the valve metals. This riser is designed to have a flange on the lower portion thereof which flange serves to contact the nonconductive sheet of material covering the cell base and provide a compressible seal therewith, thereby preventing leakage of the anolyte through the cell base. The riser then has a further extension which allows it to project through the cell base. This extension may be an integral portion of the riser or it may consist, for example, of an electrically-conductive metal stud, such as copper, which stud screws into the bottom of the anode riser and extends therefrom. In the case of the construction where the cell base is, for example, of aluminum and therefore serves as both the support and conductor, the extension of the anode riser is fastened at the bottom of the cell base by means of a nut, which nut serves to draw the flange on the anode riser into intimate contact with the sheet of nonconductive material thereby effecting a hydraulic seal. In the instance where the base is constructed of a less conductive material such as steel, a nut will also be provided which comes in contact with the bottom of the cell base and provides the force for forming the compressible seal, however, the riser will further extend through a connecting conductor and on the bottom of this conductor another nut will be provided for tightening the riser to said conductor and providing electrical contact.

Referring now to the drawings in which corresponding elements in the different figures have the same number, FIG. 1 is an end view of a typical anode and cell base assembly according to the present invention, the conventional cell can not shown. In this figure the cell base 1 is constructed of a material such as aluminum or copper and serves as both the supporting means for the cell and as the conductor. The power supply 7 is attached directly to this base, for example, by means of a nut 9 and bolt 11. The nonconductive sheet 3 covers essentially all of the cell base 1 and is constructed of an elastic material such as rubber. The

protrusions

5 and 6 on nonconductive sheet 3 perform separate functions. Protrusion 5 serves as a gasket on which the cell can rest. A small amount of putty 29 lines the inside of the protrusion to insure that no leakage occurs. Protrusion 6 serves as a deflector to prevent brine or water from getting between the non-conductive sheet 3 and the cell base 1. The anode 19 is connected, for example by welding, to the anode riser 13, which riser extends through the nonconductive sheet and cell base and is fastened on the bottom of the cell base by means of a nut 17. The riser is also provided with a flange 15 which upon tightening the nut 17, forms a hydraulic seal with the nonconductive sheet of material 3 thereby preventing leakage of anolyte through the cell base. While it is indicated in FIG. 1 that two anodes extend across the width of the cell, this number is not critical and may be changed as conditions warrant.

FIG. 2 is a partial side view along the length of an anode and cell base assembly. This figure shows essentially the same features as in FIG. 1, however, there is also indicated on the anode 19 the electrically conductive surface 21, greatly exaggerated for illustration, in fact being on the order of from 1 to 5 microns in thickness.

FIG. 3 is a cross-section of an anode and cell base assembly similar to that in FIGS. 1 and 2 with the difference that in this case the base 1 is constructed of a less conductive material. Therefore it is often desirable to use a series of connecting conductors 23 to supply the current to the individual anodes. Thus, the power supply 7 is connected to the conductors 23 by means of nut 9 and bolt 11 and nuts 27 serve to provide contact of the conductors 23 with the extension of the anode riser 13, which in this case is a copper stud 25. In this figure it is also shown that the holes in the nonconductive sheet 3 are somewhat larger than the holes in the cell base 1 thereby providing a certain amount of metal to metal contact between the anode riser 13 and the cell base 1. Not only is this desirable in that it provides an additional path for current flow in a construction such as in FIGS. 1 and 2, but it is also important to good anode alignment. The copper stud 25 is seated in the anode riser 13 by means of threads and provides an eflicient current conducting means without the necessity for intricate machining of the anode riser. This copper stud 25, however, is not required and the riser itself may extend through the cell base 1 to make contact with the current conducting means.

A cell embodying the present invention has a number of advantages as compared to the prior art cells of this type employing graphite anodes in the typical complicated and cumbersome base structure in which the anode blades are inserted in a copper grid which is then covered with a bonding layer of an electrically conductive material, such as molten lead, followed by a layer of asphalt, to prevent leakage, an finally by concrete. Beside the obvious advantages that will accure from the simplier construction of the present invention, a number of significant operating advantages are obtained. In the first place, a cell employing the instant anode and cell base assembly will exhibit a constant voltage over the total life of the cell, whereas cells of the prior art employing graphite anodes require a gradual increase in voltage in order to maintain a constant current density owing to the increase in anode-cathode gap occasioned by anode attrition. Furthermore, it is observed that, whereas the increase in voltage required to off-set the increased resistance going from the bus bar in a conventional cell to the graphite anodes is on the order of 200 milivolts, in a cell employing the anode and cell base assembly of the present invention, only an additional 25 to 100 millivolts will be required. Owing to its stability and the lessened resistance to passage of current through the assembly, it has been found that, whereas the prior art was limited to operation within the range of from 0.5-1.0 ampere per sq. inch, it is now possible to operate at good efficiency using current densities on the order of from 1-6 a.s.i. or higher. In other words, the production of the cell may be increased sixfold. Obviously then it is possible to obtain a much higher capacity using the same amount of floor space. Again owing to the lessened resistance of the anode and base assembly, a taller cell is possible, resulting in a capacity advantage. Because of the fact that the present invention does not employ materials which tend to deteriorate upon operation, such as asphalt or concrete, the purity of the products of electrolysis is significantly great- The configuration and design of the dimensionally stable anodes to be used in accordance with the practice of the present invention involve such a number of variables that in general it may be said that essentially all dimensionally stable anodes are operable. As is stated hereinabove, foraminous valve metals as well as valve metals in sheet form may be used to support the electrically-conductive surface. FIGS. 4-6 represent preferred embodiments of anode design and configuration according to the practice of the present invention. These figures are illustrative only, however, and variations in configuration and design which will occur to those skilled in the art are also useful. FIGS. 4-6 represent top views of the anodes 19 which are attached to the risers 13, typically by welding. In FIG. 4 it will be seen that the anode 19 is formed from a continuous sheet of valve metal which is bent at 33 in the form of a Z which serves to close the anode structure and provide structural support. FIG. 5 illustrates the use of two U-shaped valve metal members 31 which extend from the top to the bottom of the anode 19. The members 31 are attached to the anode 19, again by welding. FIG. 6 represents a similar anode employing only one member 31. It may also be desirable to provide the anodes with braces in order to prevent mechanical distortion of the surfaces of the anode. This may be accomplished in any number of ways, for example, by inserting three pairs of U-shaped braces (not shown) between the two anode faces with the base of the U attached to the anode riser.

Illustrative of the invention, a typical cell base is constructed from a continuous sheet of aluminum 84.9 inches by 43.0 inches and 1.5 inches thick. Into this cell base there are drilled 46 holes having a diameter of 0.77 inch into which are inserted 46 anodes comprising 23 rows. These anodes are constructed of platinum-coated titanium sheets mounted on copper-cored titanium risers and have a configuration corresponding to that shown in FIG. 6. The distance from the top of the anode to the cell base is 27.5 inches and the diameter of the riser is 1.25 inches (riser plus flange diameter, 2 inches). Into the bottom of the anode riser there is screwed, for a distance of 2 inches, a copper stud having a diameter of 0.75 inch and extending through the cell base and 2 inches beyond. The nonconductive material which covers the base consists of a continuous sheet of neoprene rubber having-46 holes therein corresponding to the holes in the cell as :but having a diameter of 1.25 inches. The sheet is fitted with ridges, one of which serves as a gasket and the other as a deflector to prevent seepage of liquids between the nonconductive sheet and the cell base.

While the invention has been described with reference to certain specific embodiments thereof, it is understood that it is not to be so limited since alterations and changes may be made therein which are within the full and intended scope of the appended claims.

We claim:

1. In an electrolytic cell for the electrolysis of alkali metal halide solutions of the type comprising an anode and cell base assembly and a cell can, the improvement in the anode and cell base assembly which comprises:

(a) a conducting and supporting cell base means having holes disposed therein for receipt of anode risers;

(b) an electrically nonconductive sheet covering the entire cell base, having holes disposed therein corresponding to the holes in the cell base and serving to provide a compressible seal between the anodes and the cell base and between the cell can and the cell base and,

(c) dimensionally stable anodes, said anodes comprising an electrically-conductive surface, a material sup porting said conductive surface and an anode riser having a flange on the lower portion thereof and extending past said flange and through the cell base.

2. A cell as in claim 1 wherein the cell base means comprises a unit construction of a highly conductive metal selected from the group consisting of copper and aluminum and provides both a mechanical supporting means and electrical conducting means.

3. A cell as in claim 1 wherein the cell base means comprises, in combination, a mechanically supporting unit construction of a less conductive metal which is iron or steel and a number of connecting conductors of a highly conductive metal to provide current to the individual anodes.

4. In an electrolytic cell for the electrolysis of alkali metal halide solutions of the type comprising an anode and cell base assembly and a cell can, the improvement in the anode and cell base assembly which comprises:

(a) a unit cell base construction of aluminum having holes disposed therein for the receipt of anode risers;

(b) a single sheet of rubber covering the entire cell base and having holes disposed therein corresponding to and slightly larger than the holes in the cell base and,

(c) in dimensionally stable anodes which comprise an electrically conductive surface, a valve metal supporting said surface and an anode riser having a flange on the lower portion thereof, said riser extending past said flange through the holes in the cell base cover and cell base and being in electrical contact with said cell base.

5. In an electrolytic cell for the electrolysis of alkali metal halide solutions of the type comprising an anode and cell base assembly and a cell can, the improvement in the anode and cell base assembly which comprises:

(a) an iron cell base of unit construction having holes disposed therein for the receipt of anode risers;

(b) a single sheet of rubber covering the cell base and having holes disposed therein corresponding to and slightly larger than the holes in the cell base;

(c) dimensionally stable anodes comprising an electrically-conductive surface, a valve metal supporting the conductive surface and an anode riser having a flange on the lower portion thereof, said riser extending past said flange through and beyond the cell base and,

(d) a series of connecting conductors in electrical contact with the extensions of the anode risers.

References Cited UNITED STATES PATENTS 3,385,779 5/ 1968 Nishiba et a1 204-275 X 3,497,446 2/ 1970 Clapper et a1. 204-242 3,558,465 1/ 1971 Colvin et a1. 204-242 X I OHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R.