US3591483A - Diaphragm-type electrolytic cells - Google Patents

Abstract

A DIAPHRAGM-TYPE ELECTROLYTIC CELL IS PROVIDED WHICH IS ESPECIALLY SUITED TO THE USE OF DIMENSIONALLY STABLE ANODES. THE CELL IS CHARACTERIZED IN HAVING A METAL 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 NON-CONDUCTIVE 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

y 6, 1971 R. E. LOFTFIELD ETAL 3,591,483

DIAPHRAGM-TYPE ELECTROLYTIC CELLS 2 Sheets-Sheet 1 Filed Sept. 27. 1968 INVENTORS RICHARD E. LOFTFIELD HENRY W. LAUB July 6, 1971 R. E. LOFTFIELD ET AL 3,591,433

DIAPHRAGM-TYPE ELECTROLYTIC CELLS Filed Sept. 27, 1968 2 Sheets-Sheet INVENTORS RICHARD E. LOFTFIELD HENRY W. LAUB BY lam ATTORNEY a G E 515 United States Patent 3,591,483 DIAPHRAGM-TYPE ELECTROLYTIC CELLS Richard E. Loftfield, Chardon, and Henry W. Laub, Painesville, Ohio, assignors to Diamond Shamrock Corporation, Cleveland, Ohio Filed Sept. 27, 1968, Ser. No. 763,121 Int. Cl. C22d 1/02 U.S. Cl. 204-252 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Diaphragm-type cells for the electrolysis of aqueous alkali metal halide brines generally employ a foraminous or perforated metallic cathode and a fluid-permeable diaphragm overlaying the cathode thereby permitting hydraulic flow of electrolyte from the anode chamber through the diaphragm and cathode into the cathode chamber. Such cells first made their appearance in the early part of the twentieth century. The fluid permeable diaphragm, by separating the anode and cathode chainbers, avoids the disturbing effects of convection currents and gas evolution, and generally inhibits migration of hydroxyl ions towards the anode. Those diaphragm-type cells most widely used today are of the circulating electrolyte type, wherein the diaphragms and cathodes may be arranged horizontally or vertically, but in most instances, at least in the United States, the arrangement is vertical. Such cells are in wide-spread use in the industry for the production of chlorine and caustic soda from sodium chloride brines and, through the use of various sophisticated modifications, considerable efficiency has been obtained from the cells which have been operated at current densities approaching one ampere per square inch. However, despite their wide-spread acceptance, these cells nevertheless have certain drawbacks and disadvantages which limit the further modification and improvement thereof.

Most of these limitations may be attributed to the fact that the majority of cells in operation to-date employ graphie as the anode material. Generally these anodes take the form of flat, vertically-disposed blades which have their lower ends embedded in the cell bottom or base. A typical means of implanting these anode blades in the cell base is described in US. Pat. 2,987,463 and consists in inserting the anode blades into the slots formed by a plurality of conductive metal grids, usually copper grids. In order to improve electrical contact, it is then the standard procedure to apply a bonding layer of an electrically conductive material such as molten lead, which layer serves both to increase electrical conductivity and rigidly set the anode blades in the conductive grid. Over this electrically-conductive bonding layer there is then applied an electrically insulating coating, for example asphalt, which prevents access of the corrosive anolyte to the metal. In turn, a layer of concrete is applied over this asphalt layer to complete the base construction. Obviously, there are a number of disadvantages to such a cumbersome technique. For instance, a portion of the effective Patented July 6, 1971 ICE anode surface, which portion generally approaches 20 percent, is lost to use since it is covered by the various base materials. Another disadvantage is found in the fact that, upon use, the concrete layer will deteriorate and particles thereof will tend to plug the diaphragm, thereby significantly reducing the effective surface area thereof and necessitating an increase in voltage if a constant current density is to be maintained. A further significant disadvantage of this construction lies in the fact that a substantial resistance to the passage of current results from the fact that the current must pass from the outside conductor through the copper base, the conductive bonding layer and finally into the graphite anode itself, each point of contact adding to the total resistance. An additional and obvious disadvantage is that the anodes themselves gradually deteriorate and after a certain period of time must be replaced. This replacement operation involves considerable effort and expense since the remaining portions of the anode blades must be manually removed from the cell base before new anodes can be embedded.

Other disadvantages and limitations arise from the nature of the anode material itself. Thus, graphite is not completely stable to the corrosive action of the brine, especially at the elevated temperatures involved in operation at high current densities. For this reason graphite anodes will deteriorate, contaminating the cell gases with carbon dioxide and organic compounds. The cell liquor is also contaminated with organic compounds, some of which contribute a blue color to the caustic when concentrated to 50 percent. These compounds also contribute fluorescent properties to the caustic which are objectionable to many caustic users. Furthermore, while graphite is an effective conductor of electricity, it nevertheless has a resistance which is high, relative to some of the materials recently available. For example, its resistance may be up to 500 times as great as that of copper. This imposes a severe limitation upon the current density at which the cell may be operated. In the past it has been necessary to operate at current densities of no greater than about one ampere per square inch since the internal resistance of the cell is such that increasing the current results in elevating the temperature of the brine to the point where boiling occurs. Also, the resistance of the graphite is such that the height of the anodes, and therefore the cell, has been limited to about 30 inches.

A further disadvantage arises from the fact that the cell liquor and chlorine gas become contaminated with chlorinated organics resulting from chlorination of the graphite, the graphite impregnants, asphalt or other materials used to seal and insulate the cell base.

Recently the chlorine-caustic industry has seen the development of dimensionally stable anodes. These anodes, as their name implies, have the advantageous property of conducting current at relatively low chlorine overvoltages while themselves exhibiting great resistance to the corrosive conditions present in chlorine-caustic cells. While dimensionally stable anodes have to-date been used mostly in mercury-type cells, the properties of these anodes would also afiord significant advantages if used in diaphragm-type cells.

STATEMENT OF THE INVENTION Therefore it is a principal object of this invention to provide a diaphragm-type electrolytic cell especially suited to the use of dimensionally stable anodes.

It is a further object of the present invention to provide a diaphragm-type electrolytic cell capable of operation at increased efficiencies and higher current densities.

It is a still further object of the present invention to provide a diaphragm cell base suited to use with dimensionally stable anodes, which base is efiicient and simple in construction.

Another object of the invention is to provide various anode designs and configurations suitable for use with the improved cell bases in diaphragm-type electrolytic cells.

These and other objects of the present invention will become apparent to those skilled in the art from the description and claims which follow.

It has now been found that these and other objects and advantages may be obtained in an electrolytic cell of the type having a cell base, a cell can, anodes and diaphragmcoated cathodes for use in the electrolysis of alkali metal halide solutions if said cell is characterized in that it 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,

(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 a cell has an 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, sodium chloride conversion and current efliciencies, allows fabrication of taller cells thereby conserving fioor space and provides a relatively constant voltage over the entire life of the cell, all as opposed to conventional diaphragm-type cells employing graphite anodes.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified end view of a typical diaphragmtype electrolytic cell applying the improved construction and advantages of the present invention with the cell can and cathodes removed for clarity.

FIG. 2 is a simplified side view of a portion of a typical diaphragm-type electrolytic cell according to the present invention again with cell can and cathodes not shown.

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 the connecting conductor to the anode riser used when the cell base is of a less conductive metal and does not serve as both a support and conducting means.

FIGS. 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 and construction of the diaphragm, the cathode or the cell can. Any of the constructions currently in use are acceptable and may be adapted to the present invention. For the purposes of illustration and in order that the present invention may be more readily understood, reference will be made to the type of construction embodied in US. Pat. 2,987,463 wherein the cathodes are in the form of parallel hollow fingers projecting horizontally from the two opposite sides of the cell can and are adapted to alternate with the anodes. The diaphragm in this type of operation is deposited upon the perforated or foraminous cathode material itself. The cell can consists of an inner and outer wall of electrically conductive material thereby forming a peripheral chamber for the collection of catholyte solution and cathode gas. Welds are used to electrically join the cathode tubes with the cell can on at least one side.

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

The conducting and supporting cell 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 be constructed of a material selected from the group consisting of copper and aluminum 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 flow 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 non-conductive, sheet of material, preferably rubber. Titanium, which is generally non-conductive 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 non-conductive 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 non-conductive layer, however, the hole need only be of the same dimension as the holes in the base. This non-conductive 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 non-conductive 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 non-conductive 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 the weight of the cell can 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 non-conductive 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 electrically-conductive 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 sulficiently 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 over-voltage 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 film-forming 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 non-conductors 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 lesser 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 non-conductive 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 non-conductive 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 cell according to the present invention with the conventional cathodes and cell can removed. In this figure the cell base 1 is constructed of a material such as aluminum or copper and hence serves as both the supporting means for the cell and 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 this non-conductive 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 non-conductive 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 non-conductive 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 a cell, again with the conventional cathodes and cellcan removed. 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 a cell base and anode assembly similar to that in FIGS. 1 and 2 with the differerence that in this case the cell base 1 is constructed of a less conductive material. Therefore it is necessary 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 non-conductive sheet 3 are somewhat larger than the holes in the cell base 1 thereby providing a certain mount 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.

As is outlined hereinabove a diaphragm-type cell embodying the present invention has a number of advantages as compared to the prior art cells of this type employing only graphite anodes in the complicated and cumbersome base structure previously described. Besides the obvious advantages that will accrue from the simpler construction of the present invention, a number of significant operating advantages are obtained. In the first place it will be found that, operating according to the practice of the present invention, a diaphragm-type cell embodying dimensionally stable anodes will exhibit a relatively constant voltage over the total life of the cell, whereas with a cell employing graphite anodes it will be found that a gradual increase in voltage will be necessitated to maintain a constant current density owing to decomposition of the anodes and plugging of the diaphragm. Thus, while the variation in voltage over a period of 270 days using a cell according to the present invention will be on the order of 0.1 to 0.2 volt, a graphite anode cell over a like period of time might be expected to require an increase in voltage of about 0.70

volt. Furthermore, it can be observed that, whereas the increase in voltage required to offset the increased resistance going from the bus bar in a conventional diaphragm-type cell to the graphite anodes is on the order of 200 millivolts, using a cell according to the present invention which employs dimensionally stable anodes and the improved cell base, only an additional 75 to 100 millivolts Will be required. Owing to the stability of the cells of the present invention and the lessened resistance to the passage of current through the various connections and the dimensionally stable anodes, it has been found that, whereas the prior art was limited to operation :within the range of from 0.51 ampere per square inch, it is now possible to operate cells at good efiiciency using current densities on the order of from 1-2 amperes per square inch or higher. In other words, the production of a cell may be doubled. Obviously then it is possible to obtain a much higher capacity using the same amount of floor space. Likewise, owing to the reduced resistance to current passage of the dimensionally stable anodes and the improved electrical connections taught by the present invention, it is also possible to increase the height of the anodes, that is the distance from the cell base to the top operating surface of the anode, by a factor on the order of 50 percent. Whereas graphite anodes were previously limited in total height to approximately 30 inches, it is now possible to construct a cell which employs anodes having a height of 45 inches, thereby again effecting a considerable increase in capacity per unit of available fioor space. Because of the fact that the present invention does not employ materials which tend to deteriorate upon operation of the cell, such as asphalt or concrete, it will be found that the diaphragms will have a longer useful life since they do not become clogged with particles of material which are released by the corrosive effect of the chlorine gas and anolyte liquor on the materials used in cell construction. For this reason the frequency of diaphragm renewal is greatly diminished. A further and significant advantage of operation according to the present invention is that the purity of both the chlorine and caustic produced in this cell is considerably superior to that of the prior art wvherein graphic anodes were used. Regarding chlorine purity, in the gases from the prior art cells it was found that carbon dioxide and chlorinated organics were present owing to the decomposition of the anodes, the binders used therein and the organic sealants used in the cell base. According to the practice of the present invention, however, it is found that chlorine purity can be considerably increased, e.g., from 98.5 percent to 99+ percent in a typical operation and that anode efiiciency in general may be improved as much as 1.0 percent, which, in a plant producing 87,500 tons per year of chlorine is equivalent to an additional 875 tons per year of chlorine.

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. While it is stated hereinabove that foraminous or perforated valve metals as well as valve metals in sheet form may be used to support the electrically-conductive surface, it should be remarked that, owing to the fact that upon start-up of the cell small quantities of asbestos will be dispersed in the electrolyte, it is desirable that the sheet form be used whenever possible since this asbestos tends to adhere to the foraminous form and thereby block portions of 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 provides 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.

In order that those skilled in the art may more readily understand the present invention, the following specific example is afforded.

EXAMPLE A cell is constructed having a cell can and cathodes such as described in U.S. Pat. 2,987,463 and containing 22 cathode tubes and two half cathodes. A 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 the 46 anodes which comprise the 23 rows of anodes. 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 non-conductive material which covers the base consists of a continuous sheet of neoprene rubber having 46 holes therein corresponding to the holes in the cell base but having a diameter of 1.25 inches. The sheet is fitted with ridges, one of which serves as a gasket to receive the cell can, and the other as a deflector to prevent seepage of liquids between the non-conductive sheet and the cell base. \After assembly, the cell is fed with a brine solution containing approximately 320 grams per liter of sodium chloride, having a pH of 3.5 and a temperature of about F. Table I below sets forth the performance data on this cell operated at a constant cell load of 40,000 amperes and compares this data with that obtained on a typical conventional diaphragm cell employing graphite anodes and also operated at a cell load of 40,000 amperes.

Table II shows the data obtained on the same cells operated at an identical cell voltage of 4.17.

TABLE II Present Prior Characteristic invention art Cell voltage 4.17 4. 17 Cell load, amperes 63, 900 40, 000 Chlorine production, tons/day 2. l3 1. 33 Caustic production, tons/day. 2. 40 1. 50

From these tables it may be readily seen that the practice of the present invention results in significant improvements in cell operation and provides considerable economies of operation.

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.

What is claimed is:

1. An electrolytic cell of the type having a cell base, a cell can, anodes and diaphragm-coated cathodes for use in the electrolysis of alkali metal halide solutions and characterized in that it comprises:

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

(b) An electrically non-conductive 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 supporting said conductive surface and an anode riser having a flan-ge 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 an 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. An electrolytic cell of the type having a cell base, a cell can, anodes and diaphragm-coated cathodes for use in the electrolysis of alkali metal halide solutions, and characterized in that: I

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

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

(c) the anodes are 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, 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. An electrolytic cell of the type comprising a cell base,

a cell can, anodes and diaphragm-coated cathodes for use in the electrolysis of alkali metal halide solutions and characterized in that it comprises in combination: an iron cell base of unit construction having holes disposed therein for the receipt of anode risers; 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; 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, the riser extending past said flange through and beyond the cell base and, a series of connecting conductors in electrical contact with the extensions of the anode risers.

References Cited UNITED STATES PATENTS 2,994,658 8/1961 Preiser et a1. 204-286 3,022,244 2/1962 Le Blane et a1 204-290F 3,298,946 1/1967 Forbes 204278 3,385,779 5/1968 Nishiba et al 204-275 TA-HSUNG TUNG, Primary Examiner US. Cl. X.R.

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