US3527688A

US3527688A - Electrolytic cells

Info

Publication number: US3527688A
Application number: US605247A
Authority: US
Inventors: Umberto Giacopelli
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1965-12-29
Filing date: 1966-12-28
Publication date: 1970-09-08
Anticipated expiration: 1987-09-08
Also published as: DE1592031A1; GB1136808A; NL6615628A; FR1510025A

Description

United States Patent 3,527,688 ELECTROLYTIC CELLS Umberto Giacopelli, Rosiguano-Solvay, Italy, assignor to Solvay & Cie, Brussels, Belgium, a corporation of Belgium Filed Dec. 28, 1966, Ser. No. 605,247 Claims priority, application Belgium, Dec. 29, 1965, 22,216, Patent 674,452 Int. Cl. Btllk 2/08, 3/00, 3/04 US. Cl. 204-242 3 Claims ABSTRACT OF THE DISCLOSURE The anodes of electrolytic cells, particularly diaphragm cells for the electrolysis of aqueous alkaline halide solutions, are fixed in troughs by means of alloys having low melting points, rather than being sealed in a layer of lead in accordance with the prior art. The current feed bars are arranged in longitudinal alignment and in electrical contact with the troughs. One trough or a plurality of troughs is assembled with each current feed bar and the troughs of each of these assemblies are enclosed in a mass of lead or polyester resin. Each of these assemblies is accommodated in a respective recess provided in a wall of the cell. The spaces between the assemblies may be filled with cement or a synthetic resin or asbestos cords to lend structural integrity to the entire anode assembly of the cell. This construction may finally be covered with conventional protective layers of cement and asphalt or a polyester resin resistant to attack by moist halogen and alkaline halide brine, or with a single protective layer of such a polyester resin.

This invention relates to a new construction for sealing or fixing electrodes in an electrolytic cell and for distributing current to the electrodes.

The construction of the present invention may be employed with respect to the fixing of electrodes in any wall of any cell. The invention, however, is particularly adapted for the fixing of anodes in the base or bottom wall of a diaphragm cell for the electrolysis of aqueous solutions of alkaline halides. This type of cell is well known and is generally used for the electrolysis of alkaline chlorides to produce chlorine and alkali, particularly the electrolysis of aqueous sodium chloride solutions to produce chlorine and sodium hydroxide. In the conventional cells of this type, the plateshaped anodes are fixed vertically in the base of the cell by means of a layer of lead in which the current feed bars, the length of which extend perpendicular to the faces of the anodes, are embedded. The lead serves both to hold the anodes in position and to conduct current from the feed bars to the anodes. The layer of lead is covered with a layer of cement and a layer of asphalt.

This construction for distributing current to the anodes and for fixing the anodes in the base of the cell has a number of serious shortcomings. Major shortcomings are the following:

(1) At the temperature of electrolysis, the asphalt layer softens, which can result in its displacement.

(2) Halogenic organic compounds which contaminate the cell can be formed by reaction of the asphalt with the halogen formed at the anodes.

(3) The replacement of any anode or row of anodes which may deteriorate in the course of electrolysis requires not only the complete disintegration of the protecting layers but also the fusion of the entire mass of lead enclosing the feed bars and the lower portions of the anodes. Due to the high cost of such replacement, it is not economically practical to do this until the end of the life cycle of the cell.

(4) The lead cast into the base of the cell contracts upon solidification. Because this mass of lead is very substantial, this contraction is correspondingly substantial and, accordingly, contact between the lead and the anodes is quite imperfect. Accordingly, there is substantial electrical resistance between the lead and the anodes whereby between the lead and the anodes there is a substantial current drop. Furthermore, since the amount of lead employed is so substantial, the substitution for the lead of an alloy which expands upon cooling, for example, a lead-bismuth alloy, would be prohibitively costly.

(5) An oxide film tends to form at the interface of the lead and the anodes and at the interface of the lead and the current feeders. This film increases the electrical resistance between the lead and the anodes and between the lead and the current feeders thus causing a substantial drop in current.

By the practice of the present invention, the foregoing problems are obviated. The present invention is particularly adapted for the arranging of anodes and current feeders on the base (bottom wall) or the cover (top wall) of a diaphragm cell for the electrolysis of aqueous solutions of sodium chloride.

According to the invention, the anodes are positioned in one or more elongated channel-shaped members, generally having a U or similar cross-section; these members may most conveniently be described as elongated troughs. With each one or more of the troughs a current feeder bar is placed in electrical contact. Preferably, the current feeder bar is attached to the troughs such as by brazing or welding. The current feeder bars are arranged in longitudinal alignment with the troughs (i.e., the lengthwise dimension of the bars is parallel to the lengthwise dimension of the troughs). The anodes are generally plates. In each of the troughs the plates are arranged in a row with one of the ends of each inside the trough. Inside each trough there is provided an alloy having a melting point preferably under 250 C. and occupying the space in the trough not occupied by the plates, the alloy thereby fixing and sealing the plates in the trough. Each trough or set of troughs attached to a feeder bar, which together with the anodes mounted in the trough or troughs comprises an anode assembly, is enclosed in a mass of lead or synthetic resin. The term enclosed" is not intended necessarily to denote entirely enclosed since the upper edges of the troughs generally are exposed until the protective layer or layers are provided.

The wall of the cell in which one or more of the anode assemblies are to be mounted is provided with a corresponding one or more recesses shaped to accommodate the final anode assemblies, i.e., the anode assemblies the troughs of which are enclosed in the above mentioned masses. All of the anode assemblies are thus arranged mutually parallel in the wall of the cell. For convenience of installation, the masses are generally made of such size that when the anode assemblies are installed in the cell wall the masses are laterally spaced from one another. In such case, it is preferred to fill the spaces between the masses with cement or polyester resin or asbestos cords in order to lend greater structural integrity to the construction. Asbestos cords act as a resilient joint which allows expansion of the anode assemblies. Finally, over the entire exposed surfaces of the construction, but for the outwardly extending unembedded portions of the anode plates, there may be provided conventional protective layers of cement and asphalt or, preferably, in place of both layers or the latter, a protective layer of a polyester resin.

When the cell is a diaphragm cell for the electrolysis of aqueous solutions of alkaline halide, particularly sodium chloride, the anodes generally are of graphite, preferably with the ends thereof which are in contact with the 3 sealing alloy plated with copper and with tin to assure the best adhesion between the anodes and the sealing alloy. However, of course, other anodes may be used, such as of platinum-plated titanium. The current feeders are made of a good electrical conductor, such as copper and the like. The troughs are also made of a good conductor, such as copper, aluminum, iron and the like. A purpose of the trough is to limit the amount of sealing alloy required and to restrict the distances which the alloy must bridge; accordingly, the alloy may be one which contracts upon solidification, such as conventional alloys of lead and tin. Because of the small quantity of alloys involved and the small bridging distances, the contraction is not sufiicient to significantly decrease the contact between the alloy and the trough and the alloy and anodes whereby there is no significant increase in resistance and, correspondingly, no significant current drop. Furthermore, the small quantity of alloy involved makes economically practical the use of alloys which expand upon solidification, which alloys are relatively expensive. The employment of alloys which expand upon solidification assures maximum contact between the trough and the alloy and between the alloy and the anodes. Expanding alloys are well known and an exemplary expanding alloy suitable for use in the present invention is that described in Belgian Pat. No. 647,406 constituted of 44.5% lead and 55.5% bismuth, by weight, and having a melting point of 124 C. Examples of other alloys suitable for use in the present invention are the following alloys which contract upon solidification, 50% Pb-50% Sn, melting point 225 C., and 33% Pb-67% Sn, melting point 180 C., and the following alloy which does not undergo any perceptible volume change upon solidification, 60% Pb40% Bi, melting point approximately 180 C., all proportions being by weight. As the synthetic resin substitute for the lead, as the polyester resin between the anode assemblies and as the polyester resin protective layer there may be employed, for example, a bisphenol resin in styrene solution, known as Atlac A38205. Of course, on the other hand, these resins may be different from one another.

The construction of the present invention greatly reduces the cost of replacing a single anode, plurality of anodes, an entire row of anodes or all of the anodes of the cell. Specifically, it is necessary only to melt the alloy portions holding the anodes in question in place. This contrasts sharply with the prior art, in which it was necessary in all instances to melt a large quantity of lead covering the entire wall of the cell on which the anodes were mounted.

The sealing alloy is selected to have a melting point between 110 C. and preferably under 250 C. Thus, the temperatures to which the alloys need be heated to expeditiously melt them to remove anodes are much lower than the temperature of about 450 C. conventionally employed to melt lead expeditiously to remove anodes therefrom. It is preferred to heat the alloy to a temperature of about 20 C. above its melting point for the removal of anodes. In the construction of the present invention, the alloy or the portion of the alloy which is to be melted may preferably be melted by means of the Joule effect. This melting may be conducted, for example, by electrically connecting one pole of the electromotive force source to the feeder bar and the other pole directly to the anode to be replaced or, after removing the protective layer or layers, to the alloy itself through a highly electrically conductive sounding rod.

Another advantage of the present invention is that it is not necessary to use any lead at all, provided that the troughs are attached to the feeder bar, preferably by brazing, so that current may flow directly from the feeder bar to the troughs. Thus, as pointed out above, a resin may be substituted for the lead. The reason that this substiution may be made is that, unlike in the prior art, the use of lead in this embodiment is not necessary for the conducting of electricity. It is preferred that the resin have a relatively high softening point, in particular a softening point above the temperature to which the alloy is to be heated for replacement of anodes. Accordingly, when, instead of lead, a resin is used, the sealing alloy must be selected to have a melting point under 250 C. When lead is used, the alloy may have a melting point as high as 300 C.

In accordance with conventional construction, between the faces of the anodes are interposed cathodes. Since each feeder bar is in longitudinal alignment with the troughs to which it is connected and, therefore, the lengthwise dimensions of the feeder bars are parallel to the faces of the anodes, any shifting of the anodes caused by successive elongating and contracting of the bars as they are heated by the flow of current during operation of the cell and allowed to cool during non-operation of the cell, has no elfect on the spacing between the anodes and the cathodes. This is another advantage of the present invention.

The invention will now be further described by reference to the drawings, in which:

FIG. 1 is a plan view of a group of anode assemblies according to the present invention-mounted in a cell;

FIG. 2 is a plan view of a single one of the anode assemblies of FIG. 1;

FIG. 3 is a vertical section of the anode assembly of FIG. 2. taken through section line 3-3;

FIG. 4 is a vertical section of the anode assembly of FIG. 2 taken through section line 44;

FIG. 5 is a partial transverse section of a cell showing some of the anode assemblies of FIG. 1 mounted in the base (bottom wall) of the cell.

Individual anode assemblies (FIGS. 2, 3 and 4) are constructed outside the cell. A copper current feeder bar 1 is attached to the outside of the bottoms of two copper troughs 2 by means of brazing. A temporary mold (not shown) is constructed about this preliminary assembly to permit subsequent casting operations. A mass of lead 5 is provided around the troughs by means of casting. In each of the troughs 2 a plurality of anodes 3 is positioned upright with their bottom ends resting on the inside of the bottom of the trough. An alloy having a melting point below 250 C. is cast into the troughs and, upon cooling, the resulting solidified alloy 4 in the troughs fixes and seals the anodes 3 in the troughs.

A plurality of the foregoing assemblies (FIGS. 1 and 5) constitutes the anodic portion of an electrolytic cell for the electrolysis of aqueous solutions of sodium chloride. The shell of the cell is of concrete and the bottom wall (base) 6 thereof is provided with recesses shaped to accommodate the assemblies. The cell casing and the individual assemblies are dimensioned so that when the assemblies are installed in the base of the cell there are lateral spaces between the assemblies. Cement or a polyester resin 7 is cast into the lateral spaces and, upon solidification, lends rigidity and structural integrity to the construction. Finally, over the construction there is provided by casting a protective layer or layers 8, which, in accordance with conventional construction, may be a layer of cement in combination with a layer of asphalt or a layer of any conventional polyester resin which is resistant to moist chlorine and to hot sodium chloride brine or may be a single protective layer of such a polyester resin.

While the invention has been described by reference to a particular embodiment thereof, it is to be understood that this embodiment is described merely as an example and it is intended that all variations within the spirit of the invention be included within the scope of the appended claims.

What I claim and desire to secure by Letters Patent is:

1. An anode assembly for the electrolysis of alkali metal halide solutions, comprising, highly electrically conductive current feeder bars, a plurality of vertical graphite plates arranged in spaced parallel rows and mechanically and conductively affixed to respective feeder bars, said graphite plates having metal covered bases, an alloy mechanically and electrically connecting the graphite plates to said feeder bars, said alloy melting under 250 C., said anode assembly comprising a plurality of separate anode units electrically independent, laterally spaced and arranged mutually parallel in the bottom of an electrolytic cell, each unit comprising one of said feed bars, at least one highly electrically conductive channel bar mechanically and condnctively aflixed thereto, arranged parallel to the length thereof and adapted to closely include said metal coated bases of said graphite plates, said low-temperature melting alloy defining a solder-type bond between said plates and said channel bars.

2. An anode assembly according to claim 1, in which said feeder bar and said channel at least one bar of each anode unit are enclosed in a mass of easily softened synthetic resin, having a high softening point, forming a compact aggregate.

3. An anode assembly according to claim 2, in which said bottom has recesses and each aggregate is accommodated in a recess in the bottom of the electrolytic cell.

References Cited UNITED STATES PATENTS 2,370,087 2/1945 Stuart 204-266 2,987,463 6/1961 Baker et al. 204-266 3,342,717 9/1967 Leduc 204-266 XR 3,390,072 6/1968 Wiseman 204-266 3,410,784 11/1968 Maunsell et al. 204-290 XR 3,425,929 2/1969 Emery et al. 204-266 ROBERT K. MIHALEK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 204-289, 294