US3583898A

US3583898A - Anode assembly for electrolytic cell

Info

Publication number: US3583898A
Application number: US788212A
Authority: US
Inventors: Umberto Giacopelli
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1968-01-03
Filing date: 1968-12-31
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08
Also published as: BE708888A; DE1813117A1; NL6900025A; FR1599572A; CH495779A

Abstract

AN ELECTROLYTIC CELL FOR ELECTROLYSIS OF AQUEOUS SOLUTIONS OF HALIDES OF ALKALINE METALS HAS AN ANODE-CARRYING BASE WITH A SHELL OF A CHEMICALLY INERT MATERIAL. CURRENT CONDUCTING BARS LIE IN PARALLEL CAVITIES IN THE BASE AND GRAPHITE ANODES HAVE THEIR LOWER EDGES RESTING ON THE BARS IN A LAYER OF LOW MELTING POINT ALLOY. SYNTHETIC RESIN SET IN PLACE IN THE CAVITIES OVER THE ALLOY ASSURES A SEAL. ADJACENT CAVITIES OVER THE ALLOY ASSURES A SEAL. ADJACENT CAVITIES ARE ELECTRICALLY CONNECTED IN PAIRS TO PERMIT MELTING OF THE ALLOY AND SETTING OF THE SYNTHETIC RESIN SEAL BY A HEATING CURRENT PASSED THE TWO CAVITIES OF A PAIR.

Description

June 8, 1971 u. GIACOPELLI ANODE ASSEMBLY FOR ELECTROLYTIC CELL Filed Dec. 31, 1968' 4 Sheets-Sheet 1 Jig-.

June 8, 1971 u. GIACOPELLI 3,583,898

ANODE ASSEMBLY FOR ELECTROLYTIC CELL Filed Dec. 31, 1968 4 Sheets-Sheet 2 JII All

U. GIACOPELLI ANODE ASSEMBLY FOR ELECTROLYTIC CELL June 8, 1971 4 Sheets-Sheet 3 Filed Dec. 31, 1968 June 8, 1971 u. GIACOPELLI 3,583,393

' ANODE ASSEMBLY FOR ELECTROLYTIC CELL Filed Dec. 31, 1968 4 Sheets-Sheet w M m- 15 r 22 25 19 i 1 a 1 l E 27 l a 18 I a) 1 17 \& zz'gnrj m -5 B 9 United States Patent Int. Cl. zzd 1/02 U.S. Cl. 204-286 18 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell for electrolysis of aqueous solutions of halides of alkaline metals has an anode-carrying base with a shell of a chemically inert material. Current conducting bars lie in parallel cavities in the base and graphite anodes have their lower edges resting on the bars in a layer of low melting point alloy. Synthetic resin set in place in the cavities over the alloy assures a seal. Adjacent cavities are electrically connected in pairs to permit melting of the alloy and setting of the synthetic resin seal by a heating current passed between the two cavities of a pair.

The invention relates to a new structure of the anodecarrying base for electrolytic cells of the type having a series of parallel electrodes designed in particular for the electrolysis of aqueous solutions of halides of alkaline metals and provided with means for feeding electric current, sealing means for the electrodes and protection against corrosion.

In conventional cells of this type, the anodic plates, which are generally graphite, are fixed vertically in a base of reinforced concrete by means of a layer of lead assuring electric contact and coated with a layer of cement and/or a layer of asphalt sometimes itself covered with a layer of cement. The current conducting bars are embedded in the layer of lead perpendicularly to the anodic plates.

This mode of feeding the electric current and of sealing the anodes involves serious inconveniences of which the principal ones are as follows:

At the temperature of electrolysis, the asphalt layer is subject to a certain softening which can result in its displacement.

If the asphalt is in contact with the electrolyte, it can, by reaction with the halogen formed on the anodes, produce halogenated organic compounds which can contaminate the halogen or form muds which seal the diaphragm.

It is impossible to replace a particular anode (or row of anodes) which has become broken or has deteriorated in the course of the electrolysis. In effect, the replacement of the anodes requires not only complete destruction of the protective layers but even the melting of the Whole mass of lead which receives the current conductors and the bases of all of the anodes. For obvious economic reasons, such operations can be carried out only at the end of the life cycle of the cell.

The large mass of lead cast in the base of the cell retracts on solidification. This results in an imperfect contact between the lead and anode which is responsible for an important ohmic drop. The substitution for the lead of an alloy which expands on solidification, or at least does not contract as much, such as certain lead-bismuth alloys would represent a considerable investment which would necessarily be reflected in the cost of production.

When the lead is cast, there is produced at the interface between the lead and the anode or between the lead and the current conductors an oxide film which increases the electrical resistance of the assemblies.

ice

If the cement is in contact with the electrolyte, it inevitably transfers calcium or magnesium ions which sooner or later seal the diaphragm.

A perfect seal between the concrete base and the partitions of the cell, usually of iron, being extremely difficult to realize, there occurs a seepage of the brine which causes fissures in the concrete and dangerously corrodes its metallic reinforcement.

[[n view of their weight, the concrete bases are delicate to manipulate so that this can be done only by machine.

These inconveniences have been partially remedied by the invention described in my copending patent application Ser. No. 605,247 filed Dec. 28, 1966'. Nevertheless, the replacement of the anodes still requires the destruction of the protective coating. Moreover, the melting of the alloy by the Joule effect is prohibited since the copper sections constitute a preferential path for the passage of the current.

The present invention makes it possible to overcome all of these inconveniences. It relates to an anodic assembly for electrolytic cells comprising an anode-carrying base provided with parallel cavities extending substantially throughout the cell and each including a current conducting 'bar extending through a side of the base, the bottoms of a row of vertical anodic plates resting on the bar and a bedding or sealing alloy having a low melting point, characterized in that at least the part of the base which is in direct contact with the electrolyte in the course of the electrolysis is formed of an insulating and chemically inert material while in each cavity the sealing alloy is protected from attack by the electrolyte and the products of electrolysis by a synthetic resin which is cast on the said alloy and is set in situ by the effect of heat to form an easily removable elastic joint which assures at the top of each cavity a fluid tight seal between the anodic plates and the insulating and inert material of the base.

The invention will be more fully understood from the following description and from the illustrations shown by way of example in the drawings in which:

FIGS. 1 to 5 are schematic cross sections illustrating different embodiments of an anode-carrying base in accordance with the invention;

FIG. 6 is a top plan view of one particular embodiment of a complete anodic assembly;

FIGS. 7 and 8 are respectively a cross section and a longitudinal section of a cell equipped with such anodic assembly, and;

FIGS. 9 and 10 are schematic partial sections showing electrical connection of adjacent cavities.

In FIGS. 1, 2, 4 and 5, only the shell 1 of the anodecarrying base is formed of an insulating and chemically inert material capable, for example, of resisting wet chlorine and chlorine-containing brine up to C. as, for example, a polyester resin reinforced with glass fibers.

In FIG. 3 the same inert material constitutes not only the shell of the base but also its internal structure 2 of honeycomb type with cells or cavities which assures a rigidification of the assembly without internal stresses. If desired, the rigidity of the structure can be still further improved by introducing into the cells a foam of synthetic resin 3 which is expanded and solidified in situ. The cellular structure has the advantage of permitting a circulation of air in the base itself, under the shell and around and under the parallel cavities, which assures the cooling of the base of the anodes during electrolysis.

In FIGS. 1, 2, 4 and 5, on the contrary, the rigidification of the assembly is assured by means of reinforced concrete. The shell itself, after being turned upside down, serves as the form, the mortar 4 being cast therein after putting in place the metallic reinforcements 5 and (in FIG. 2) element 6 formed of plastic material, for ex ample expanded PVC, intended to lighten the base.

Adherence between the concrete 4 and the shell 1 is assured by anchoring projections 7 which extend inwardly from the inner surface of the shell and into the concrete 4.

In 'FIGS. 1, 2 and 3 the parallel cavities 8, which are seen in cross section, are formed by recesses in the shell of insulating and inert material which thus forms partitions between the cavities. In FIG. 5 only the upper portions of the cavities 8 are formed by the inert shell, while their lower parts are formed of refractory and acid resisting cement 9 which is cast in the inverted shell previously provided with removable molds placed in each cavity. The reinforced concrete 4 is put in place after the refractory cement has set. Preferably, the two materials are sparated by a layer 10 (FIGS. 7 and 8) of an impermeable and inert material such as synthetic resin.

In FIG. 4 the shell 1 does not form the cavities 8 but presents a basin with a flat bottom on which rests, sideby-side, a series of tubes 11 of insulating and chemically inert material, for example polyester resin reinforced with glass fibers. These tubes are joined with one another and are provided at their tops with longitudinal slots i12 for the introduction of the anodic plates (not shown). The tubes traverse one of the lateral sides of the base and extend outside in order to protect from corrosion the current conducting bars which they are designed to shield. Indeed, in the four other modes of construction illustrated in FIGS. 1, 2, 3 and 5 the extremities of the copper bars 13, visible in the plan view of FIG. 6, are at the mercy of possible seepage of the electrolyte.

Whichever type of structure is adopted for the base, the interior of the parallel cavities 8 is advantageously covered with a lining 14 of plastic material resistant to heat and nondeformable, such as an epoxy resin preferably reinforced by glass fibers or other reinforcing material.

FIG. 6 shows in plan a complete anodic assembly, that is to say, a base provided with anodic plates 15, the subjacent current conducting bars 13 of which only the extremities are visible and the sealing alloy 18 (FIG. 7) protected from corrosion by elastic joints 19. For clarity of the drawing, there are shown only six parallel cavities. However, it is evident that the number of cavities as also the number of anodes is purely arbitrary and in no way limits the scope of the present invention. Each anode can be formed of any appropriate material which is a good conductor of electricity such as graphite, magnetite, titanium or its alloys coated with precious metals or compounds thereof. The parallel cavities are electrically connected by means of bridge 16 at the side of the base opposite that from which the ends of the bars 13 protrude.

Electrical connections between parallel cavities can be provided in the base itself by means of an opening or passageway through the partition separating two contiguous cavities. In the case of tubes arranged side by side (FIG. 4), it is sufficient to provide a simple perforation in the two adjacent partitions at their point of tangency to establish between the two cavities an electrical connection by the sealing alloy of the anodes. In the other structures illustrated in FIGS. 1, 2, 3 and 5 the connections by pairs are advantageously obtained by making each pair of cavities in the form of a horizontal U (FIG. 6). In this case, the sealing alloy forms a connecting bridge 6 by spreading after the copper bars 13 have been put in place into the single groove common to the two rows of contiguous anodes. Whatever the structure of the base, the electric coupling can likewise be provided, as illustrated in FIG. 9, by a metallic conductor 40 for example of titanium or copper coated with titanium, in the form of an inverted U spanning the partition separating the two cavities to be connected and fixed in place by their two extremities embedded in the sealing alloy on opposite sides of the partition.

The electrical coupling can also be provided, as illustrated in FIG. 10, by a removable conductor 41 temporarily connecting two bolts 42 of conductive metal disposed on opposite sides of the sparating partition, the head 43 of'each bolt being embedded inthe sealing alloy 18' and the thread, coated with titanium, emerging from the alloy and receiving nuts 44 for securing the conductor. The electrical couplings are located at the ends of the cavities opposite those at which the ends of the bars extend. In FIGS. 9 and 10 the seal 19 has been omitted.

FIGS. 7 and 8 show respectively a cross section and a longitudinal section of a diaphragm cell equipped with the refractory cement base shown in FIG. 5.

The anodes are put in place in the following manner: After having introduced into the parallel cavities, the copper bars 13, the shape of Which corresponds to that of the bottom of the cavities, and possibly the metallic conductors for electrically coupling each pair of cavities, the orifices 17 through which the bars extend through the side of the base are carefully closed and an alloy 18 having a low melting point and low shrinkage on solidification, such as the lead-bismuth alloy described in my application Ser. No. 605,247, is poured into the cavities. The alloy 18 partially solidifies. An electric current of appropriate intensity is then applied to' the'free ends of two bars 13 which are electrically coupled in such manner as to bring the alloy back to its melted state and raise its temperature to a selected value (approximately 250 C.). The previously coppered and tinned extremities of the graphite plates 15 are then placed in the melted alloy 18 so as to come into contact with the bars 13. This procedure is then repeated on the adjacent pair of parallel cavities.

In order to protect the bases of the anodes and the sealing alloy against corrosion by the chlorine-containing brine, there is poured onto the sealing alloy in the parallel cavities a latex of polyvinyl chloride judiciously plasticized so as to set in situ at a heat below the melting point of the alloy. For example, it is heated for a period of two hours between and C. by the Joule effect obtained by passing a current through two electrically coupled bars as for the melting of the alloy. There is thus obtained a uniform and continuous covering which constitutes a chemically inert elastic joint 19 assuring perfect fluid tightness between the anodic plates 15 and the inert shell 1 of the base. 7

Before casting the latex, the surfaces of the graphite, the alloy and the partitions (surfaces in contact with the latex) are advantageously coated with an adhesive undercoating, for example an epoxy resin, which improves the adherence between these materials and the polyvinyl chloride.

The parallel cavities can have any desired section but are advantageously narrowed at the top as can be seen in the cross sectional views in such manner as to retain firmly between their lips the elastic joint and to prevent its detachment or accidental displacement.

On the anodic assembly thus realized, there is positioned the metallic cathode case 20 of which the cathode elements 21 which are made of wire netting or perforated sheet metal support a diaphragm of asbestos fibers not shown). The cathode elements 21 are advantageously tapered at the base as seen in FIG. 7 in such manner as to avoid local. thickening of the diaphragm when it is deposited and an anode-diaphragm contact due to local enlargement thereof in the course of the electrolysis. The cathode case 20 is provided with

conduits

22 and 23 for the evacuation of the lye and the hydrogen respectively, a safety conduit 24 and the cathode current lead 25. Fluid tightness between the base 1 and the casev 20 on the one hand and between the case 20 and the cover 26 on the other hand is assured by

gaskets

27 and 28 resistant to the chlorine-containing brine.

The cover 26 is formed of polyester reinforced with glass fibers or of polypropylene reinforced with perforated sheet metal. It carries a brine inlet 29, a chlorine outlet 30 and a level indicator tube 31.

A member 32 in the form of a comb resting on the electrodes maintains a constant anode-cathode spacing.

The spaces 33 for the cathodes have their edges substantially parallel. The spaces 34 for the anode plates are of trapezoidal form, larger at the base than at the top, so that when the anodes are new only the extremities of the teeth 35 are inserted between the electrodes. As they are used up, the graphite plates engage further in these spaces which are provided for them. This device, which avoids all anode-cathode short circuits, can be formed of any material which resists the electrolyte and the products of electrolysis and which has sntficient rigidity at the operating temperature of the cell. Its density is preferably greater than that of the electrolyte so that the comb 32 does not float on the surface of the electrolyte. Polyester resin and polyvinyl chloride are particularly suitable as materials for its construction.

In the cell described above, there is definitely eliminated all contact between the chlorine-containing brine or wet chlorine and the concrete or asphalt and at the same time, all of the inconveniences consequent to such cont-act.

The connection of the parallel cavities by pairs permits melting of the alloy and the setting in situ of its protective joint by the heating eifect obtained by the passage of electric current.

The elasticity of the joints set in situ according to the present invention permits (after emptying the cell) removing them like simple stoppers. This provides the possibility either of replacing any defective anodes or of renewing all of the anodes without breaking any part of the base.

After substitution of the anodic plates by melting of the alloy, the casting of new latex either partially (in one or more pairs of parallel cavities) or totally (in all of the pairs of cavities) followed by its gelling by heat is sufficient to reconstitute the protective layer.

It will be understood that the features of the several embodiments shown by way of example in the drawings are mutually interchangeable in so far as they are compatible.

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

'1. An anode assembly for an electrolytic cell comprising a base having a plurality of parallel anodereceiving cavities open at their tops and separated by partitions, a current conducting bar lying in each of said cavities and extending through a side of the base, a low melting point sealing alloy overlying said bar in each said cavity, vertical anode plates having their lower edge portions extending into said alloy in each said cavity and resting on said bar, at least those portions of said base exposed to the electrolyte of said cell being formed of an insulating and chemically inert material, and a seal of synthetic resin set in situ in each said cavity overlying said alloy to form an easily removable plastic joint providing a hermetic seal between said anode plates and adjacent portions of said base.

2. Assembly according to claim 1, in which said cavities of the base are convergent at their tops.

3. Assembly according to claim 1, in which the insulating and chemically inert material of the base is a polyester resin reinforced with glass fiber.

4. Assembly according to claim 1, in which the parallel cavities of the base are lined interiorly with a thermostable resin having a low coefiicient of thermal expansion.

5. Assembly according to claim 4, in which said thermostable resin having a low coefiicient of thermal expansion is an epoxy resin.

6. Assembly according to claim 1, in which pairs of adjacent cavities are electrically inter-connected adjacent the ends of the cavities opposite the side of the base through which said current conducting bars extend.

7. Assembly according to claim 6, in which said electrical connection comprises a bridge of said sealing alloy extending through a passageway connecting said adjacent cavities.

8. Assembly according to claim 6, in which said electrical connection comprises an inverted U-shaped conductor straddling the partition between said adjacent cavities and having its opposite ends embedded in said sealing alloy in said cavities.

9. Assembly according to claim '6, in which said electrical connection comprises metallic bolts having heads embedded respectively in the sealing alloy in said adjacent cavities and a metallic conductor removably secured to said bolts to provide an electrical connection between them.

10. Assembly according to claim 1, in which said insulating and chemically inert material is formed as a hollow shell of said base.

11. Assembly according to claim 10, in which said shell is provided with anchoring projections on its inner face and in which concrete is cast in said shell, while inverted, to rigidify said base, said projections assuring adherence of the concrete to said shell.

12. Assembly according to claim 10, in which said base has a rigidifying internal cellular construction of said insulating and chemically inert material integral with said shell.

- 13. Assembly according to claim 10, in which synthetic resin foam is set in situ inside said shell to provide rigidity.

14. Assembly according to claim 10, in which said shell forms said parallel cavities of the base.

15. Assembly according to claim .10, in which said shell is provided with parallel openings providing the upper portions only of said cavities, lower portions of said cavities being of refractory anti-acid cement cast in situ with suitable molds.

16. Assembly according to claim 10, in which said shell forms a flat bottom basin and in which parallel tubes of insulating chemically inert material lying horizontally side-by-side on said bottom and having longitudinal windows at their upper sides provide said cavities.

17. Assembly according to claim 16, in which adjacent ones of said tubes are bonded together.

18. Assembly according to claim 16, in which said tubes extend out through one side of said base.

References Cited UNITED STATES PATENTS 3,507,772 4/ 1970 Silsby 204286 3,498,903 3/1970 Kamarjan 204-286 3,425,929 2/1969 Emery et a1. 204P286 3,345,283 10/1967 Shibaza et a1. 204-288 2,742,419 4/1956 Baker et a1. 204-266 TA-HSUNG TUNG, Primary Examiner S. S. KANTER, Assistant Examiner U .S. Cl. X.R. 204-2166