US2951026A - Mercury cathode electrolytic cell - Google Patents

Description

2 Sheets-Sheet 1 Filed June 21, 1957 R. Y O T. M V

Aug". 30, 1960 G..MESSNER I MERCURY CATHODE ELECTROLYTIC CELL 2 Sheets-Sheet 2 Filed June 21, 1957 n I L r 2,951,026 MERCURY CATHODE ELECTROLYTIC CELL Georg Messner, Milan, Italy, assignor to Oronzio de Nora Impianti Eiettrochimici, Milan, Italy, a corporation of Italy Filed June 21, 1957, Ser. No. 667,165 Claims priority, application Germany June 28, 1956 15 Claims. (Cl. 204221) cury cathode in an electrolytic apparatus requiring as little floor space as possible has been the object of much effort for a long time, especially in the chlorine-alkali industry.

In order to attain the above result, two methods have been proposed so far, one of which consists of increasing the electrode current density, while the other is based upon devices allowing the mercury cathode surface to be kept vertical rather than horizontal. As to the former of such methods, a limit seems to have been reached by now in the maximum utilization of the cathode surface area, since any further increase in current density would cause the cell voltage to reach too high a value.

On the other hand, the use of a vertical mercury cathode has also not been found quite satisfactory. This method involves some other difficult problems such as, for instance, the provision for a proper adjustment of the graphite anodes. In addition, many cell types of vertical construction suffer from the disadvantage of facilitating the recombination of alkali with chlorine, so that the cathode must be protected from chlorine attack by some kind of diaphragm, which entails other constructional diiiiculties as well as an undesired increase in voltage drop. f

It is an object of this invention to present an-electrolysis apparatus having a horizontal mercury cathode and occupying a relatively small floor space per cathode area.

A further object is to provide an electrolysis apparatus having a number of superimposed horizontal mercury cathodes.

Another object is to provide a horizontal mercury cathode electrolysis cell having a number of superimposed electrolysis compartments.

Still another object is to provide a horizontal mercury cathode electrolysis cell having a relatively large vertical dimension and a relatively small cross-sectional area.

A further object is to provide a method for electrolyzing electrolytic solutions with a mercury cathode, whereby recombination of electrolytic products is prevented and proper adjustment of the distance between electrodes is possible. 7

These and other objects of my invention will become apparent as the description thereof proceeds.

The above advantages may be attained and the disadvantages of prior constructions overcome by the use of my invention which is an electrolysis apparatus of the mercury cathode type that allows a substantial saving in floor space even though keeping the mercury cathode surfaces horizontal or nearly so. This is made possible by the novel feature of using a plurality of superimposed rotating circular plates to support the mercury. The circular plates may be perfectly fiat and horizontal on their upper surface or can be given a slight slope preferably toward the center, so as to assume a hollow conical shape.

2351,26 Patented Aug. 30, 1960 ice Referring to the figures which illustrate specific embodiments of my invention, Fig. 1 illustrates a sectionalplan view of one tray of my preferred apparatus taken along the line A--A of Fig. 2 of a cell having horizontal plates. Fig. 2 represents a sectional side view of the same cell as shown in Fig. 1, taken along the line BB.

Fig. 3 illustrates a cell embodying circular plates sloping downward towards the center, and anon-vertical axis.

Fig. 4 illustrates a cell showing the enclosed top and base of the shell, having a non-vertical axis and sloping plates, and which embodies a different structure for the withdrawal of mercury amalgam.

In Figs. 1 and 2, the cell is composed of a cylindrical shell 16 with its axis disposed vertically. Along the axis of shell 16 there is a hollow shaft 6. The electrolysis compartments C in the cell are arranged horizontally, one above the other, throughout the height of shell 16. Each electrolysis compartment is made up of a circular fiat plate 2 attached to shaft 6 and having a rim 3 at its periphery, a set of fixed anodes 9 provided with bus bar connections 1i) arranged above the cathode plate and grouped radially around hollow shaft 6, electrolyte feed pipe 11 with a distributor 12, a mercury feed pipe 5, and a weir l. V

The general set-up of the electrolytic cell can be arranged so as to obtain an assembly of unipolar type, that is a cell in which all of the cathodes are at the same potential with respect to one another, which is'also true of the anodes. in this case the cathode plates can be all connected to the negative line through the common driving shaft 6. The movement of shaft 6 causes the plates 2 to rotate within the shell 16 about the axis of the shell. When flat plates 2 are used as shown in Figs. 1 and 2, weir 1, comprising a fiat strip of flexible and electrically non-conductive material, is arranged radially slightly above each plate so that there is a small space between the bottom of the Weir and the horizontal surface of the plate. The weir 1 is fixed While the plate surface moves tangentially underneath it, and the function of the Weir is to allow the mercury stream that flows from the feed pipe 5 to build up a pool 4 of mercury on the plate, which is contained by the brim 3 of electrically nonconductive material which surrounds plate 2. As illustrated in Fig. l a space is left between anodes 9a and 9b in which the mercury pool 4 is maintained. The plates are illustrated in Fig. 1 as rotating clockwise so that the plate moves into the pool formed by a hold back means such as weir l. The plates could, of course, rotate in the opposite direction, in which case the amalgam would be introduced on the opposite side of weir 1 from that shown in Fig. 1.

The alkali metal that is discharged upon the amalgamated plate during a complete revolution of this is dissolved in the mercury pool 4, where fresh mercury is fed from the pipe 5 and forms amalgam which leaves the latter, streaming through drain slots 15 that discharge it into the hollow shaft 6. These discharge drain slots are provided with hydraulic seals. At the same time, a minor part of the amalgam forming pool adheres to the surface of the rotating plate and is able to pass beneath the weir 1 in the form of a thin layer of dilute amalgam. This amalgam layer will act as a cathode, thus gradually increasing its alkali metal concentration throughout a complete revolution until reaching the mercury pool 4 and passing beneath weir 1 again. I

The above described procedure can obviously also be applied when conical cathode plates are used, as shown in Fig. 3. In this case, however, the provision of a weir described hereinafter. Moreover, the plates may rotate in either direction.

A particularly suitable way of using cathode plates of conical shape consists of tilting the shaft 6 slightly from the vertical direction as shown in Figs. 3 and 4, until one generatrix in each conical surface lies horizontal, or nearly so, While the opposite generatrix acquires a slope forming with respect to the horizontal plane an angle twice as large as the tilt of the shaft from the vertical direction.

A mercury pool 4 will form in a restricted area on the horizontal 'gcneratrix plane of trays 2 since the mercury feed pipe 5 is located over the horizontal portion of this plane and the plates 2 are surrounded by a brim 3 of electrically non-conductive material. The whole plate surface passes under the pool and under the rows of fixed anodes during a complete revolution so that the amalgam layer, which is adhering to the metal plate surface and is concentrated with sodium discharged in the cathodic process coming into the pool, is replaced with an outgoing layer of dilute amalgam.

The upper surfaces of the cathodic plates are made of a conducting metal, as for example steel, while the lower surfaces must be electrically non-conductive and chemically resistant to the electrolyte as well as to the anodic product such as chlorine. The lower surface may be any suitable plastic or hard rubber material or a plastic or hard rubber coating on a steel plate.

According to one embodiment of the present invention, the hollow shaft 6 is made of sufficiently thick and electrically conductive material, so as to afford sufiicient mechanical rigidity and act as an electric current lead to be connected with the negative line.

Another embodiment of the present invention consists of using a hollow shaft 6 and providing it with an inner diameter suficiently large to form a reaction chamber for the decomposition of the amalgam that is discharged into it through one or more of the slots from the pool 4. As previously explained, mercury enters the pool 4 on the periphery, passes through it in radial direction and finally is discharged through the slots in the shaft 6 into the amalgam decomposition chamber formed in the shaft cavity.

Above the amalgamated cathodic surfaces are arranged the anodes 9, of any suitable and conventional material, such as graphite, which is particularly suitable for the electrolysis of alkali chlorides, or a lead-silver alloy for the electrolysis of a sodium sulphate solution. In the latter case the interposition of a suitable diaphragm is required between each cathode and each corresponding set of anodes. V

The anodes 9 can rotate with the cathodes. However, it is more advantageous to keep them at rest. According to one feature of the present invention, a particularly convenient arrangement consists of conveying the electric current to the outer periphery of each anode through the connection 10. Such arrangement, beside providing a liberal spacing for the required number of electric connections, gives a further advantage in that the electric current is thus conveyed through the largest cross-section as presented by the anodes on their peripheral sides. This is most advantageous with graphite material, in view of its rather poor electrical conductivity, since by such arrangement it is possible to keep the voltage drop throughout the anode'material down to a minimum value.

Fig. 4 shows another embodiment of the present invention in which means are provided for a particularly simple method of adjusting the spacing between anodes and cathodes without requiring the electrolysis current to be interrupted. This is obtained by the axial shifting of the'system composed of the shaft 6 and cathodes 2. In this way it is possible to keep the electrodes spacing, and therefore also the cell voltage,at a practically constant value during the electrolysis process, irrespective of anode consumption.

The fresh electrolyte is fed into the cell over each rotating plate by means of pipes 11, which pass through the cylindrical shell 16 of the electrolysis cell and extend to near the outer wall of the shaft 6, where they join with ring-shaped distributors 12 provided with a plurality of holes 13. Theelectrolyte distributing system is made of material chemically resistant to the electrolyte and chlorine.

The depleted electrolytic solution leaves the space between the electrodes at the periphery thereof and then flows upward or downward along the shell 16, until it reaches the base 20 of the cell, and leaves the shell through outlet 21 which leads to an overflow not shown.

When the electrolysis process gives rise to some gaseous product at the anode, such as chlorine, this finds its way through the electrolyte until reaching the downward-facing side of the next upper cathode plate, along which it flows radially toward the annular space between the electrodes and the shell 16. Then the gaseous product will bubble upward through the electrolyte, until reaching the gas dome 13 at the top wherefrom it is conveyed out of the cell through an outlet pipe 19. Any suitable seal joints, not shown on the drawings, may be provided at the points where gas dome 18 and base 20 make contact with the rotating shaft 6.

The same construction and operating principles can apply to any other kind of electrolysis using a mercury cathode. The most suitable anode material will be used for any particular process, and diaphragms will be placed between anodes and cathodes whenever required.

Fig. 4 shows another particularly convenient embodiment of the invention, in which the system formed by the shaft -6 and the cathode plates 7 is composed of an assembly of equal elements 14 upon one another. Specially V-shaped spigot-and-socket joints are provided between each section and the next one in the assembly, such as illustrated in Fig. 4 showing a cross-sectional View through the shaft center-line which can usually be employed as drain passageways 15a for the amalgam from the electrolysis compartment into the hollow shaft, and which form hydraulic seals.

According to another embodiment of the present invention, the same constructional principles as disposed above can he usually employed also for a bi-polar type assembly. For this purpose all the cathode plates are electrically insulated from one another and each one is connected by a suitable electrical conductor with the next underlying anode. In this case, all paths through the electrolyte that might provide a shunt for the current between the positive and the negative pole are made as narrow and as long as possible, for instance by baflling devices.

A cell-type conforming to the constructional and operating principles as disclosed above, beside allowing the electrolysis process to be performed as satisfactorily as in any horizontal cell of conventional design, affords the advantages of requiring substantially less floor space and permitting a simpler adjustment of the electrodes spacing. Furthermore, the constructional features as disclosed above make it possible to designcells having a unit production capacity that has never been reached so far.

A horizontal 120,000 amp. cell of conventional-design, which produces about 4 short tons of chlorine per day requires a floor space of about 700 sq. ft. including aisles. A cell of the same capacity but of the type as described and based on this invention would require less than 250 sq. ft. of floor space. 7

While I have recited specific embodiments of my cell, it will be understood that various modifications may be made without departing from the spirit of the disclosure or the scope of the following claims.

I claim:

1. An electrolytic apparatus having a mercury cathode, which comprises a hollow rotating cylindrical shaft dispo sed substantially vertically, a plurality of circular plates attached to said shaft externally along its axis, anodes and supporting means therefore above each of said plates, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, and conduit means communicating with said plates through said shaft for withdrawing amalgam from each of said plates.

2. The apparatus of claim 1 wherein the hollow cylindrical shaft is made sufiiciently large in diameter to be used as a reaction chamber for decomposition of amalgam discharged into it from the circular plates in said shaft through the slots.

3. The apparatus of claim 1, wherein all cathodes are electrically connected together.

4. The apparatus of claim 1, wherein the cathode plates are electrically insulated from one another, each cathode plate being connected to the adjacent anodes, to form a system of series-connected bipolar cells.

5. An electrolytic apparatus having a mercury cathode, which comprises a hollow rotating cylindrical shaft disposed substantially vertically, a plurality of circular plates attached to said shaft externally along its axis, a rim around each plate, anodes and supporting means therefor above each of said plates, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, an electrically non-conductive narrow, flexible strip disposed radially and slightly above each horizontal plate to form a weir to retain a mercury pool over said plate and spread the mercury over said rotating plate, and conduit means communicating with said plates through said shaft for withdrawing amalgam from each of said plates.

6. An electrolytic apparatus having a mercury cathode, which comprises a hollow rotating cylindrical shaft disposed substantially vertically, a plurality of flat circular plates attached to said shaft externally along its axis and perpendicular to said axis, anodes and supporting means therefor above each of said plates, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, and conduit means communicating with said plates through said shaft for withdrawing amalgam from each of said plates.

7. An electrolytic apparatus having a mercury cathode which comprises a hollow cylindrical shaft disposed substantially vertically, a plurality of circular plates attached to said shaft externally along its axis, the upper surfaces of said plates having a hollow conical shape, anodes and supporting means therefor above each of said plates, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, and conduit means communicating with said plates through said shaft for Withdrawing amalgam from each of said plates.

8. An electrolytic apparatus having a mercury cathode which comprises a hollow cylindrical shaft, a plurality of circular plates attached to said shaft externally along its axis, the upper surfaces of said plates having a hollow conical shape, anodes and supporting means therefor above each of said plates, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, and conduit means communicating with said plates through said shaft for withdrawing amalgam from each of said plates, wherein said hollow shaft is tilted until one generatrix of the conical plate is substantially horizontal.

9. An electrolytic apparatus having a mercury cathode, which comprises a hollow cylindrical shaft disposed substantially vertically, a plurality of circular plates attached to said shaft externally along its axis, anodes and supporting means therefor above each of said plates, said anodes being stationary, disposed radially around said hollow shaft and provided with electrical connections at their peripheral sides, a shell enclosing said shaft and plates, means in said shell for introducing an electrolytic solution and mercury onto each of said plates, and conduit means communicating with said plates through said shaft for withdrawing amalgam from each of said plates.

10. An electrolytic apparatus having a mercury cathode, which comprises a plurality of identical circular plates having short segments of a hollow cylinder of the center thereof, said segments being adapted to permit the circular plates to fit in a superimposed position whereby a hollow cylindrical shaft disposed substantially vertically is formed, said shaft containing slots forming a hydraulic seal between said segments for the withdrawal of amalgam, anodes above said plates, a shell enclosing said shaft and plates, and means in said shell for introducing an electrolytic solution and mercury onto each of said plates.

11. The apparatus of claim 10 wherein the distance between the anodes and cathodes may be maintained constant by axial adjustment of the circular plate elements without interruption of the electrolysis process.

12. An electrolytic apparatus having a mercury cathode, which comprises an upright cylindrical shell, a hollow shaft along the axis of said shell, a plurality of horizontal electrolysis compartments spaced externally along the axis of said shaft, each compartment comprising a circular cathode plate, anodes and supporting means therefor above said plate, and means to supply an electrolytic solution and mercury to the top of said plate, and conduit means communicating with said plates through said hollow shaft for withdrawing amalgam from each electrolytic compartment.

13. In a mercury electrolytic cell, a cathode element comprising a circular plate structure having a segment of a hollow cylinder at the center thereof, said cylinder segment being adapted on the top and bottom edges to fit against the cylinder segments of identical cathode elements in such a manner that slots for the passage of mercury and amalgam remain, whereby an assembly of said elements may be made to comprise a hollow shaft having a plurality of circular plates externally along the axis thereof and slots through said shaft at each plate for the passage of mercury and amalgam.

14. In a mercury electrolytic cell, a cathode element comprising a segment of a hollow cylinder having a circular plate surrounding it and perpendicular to the axis thereof, the upper edge of said segment being grooved and the lower edge being tongued in such a manner that the upper edge will fit into the lower edge of an identical element and the lower edge will fit into the upper edge of another identical element, said upper and lower edges of the elements being further adapted to leave slots which form hydraulic seals between elements for the passage of fluids through the cylinder walls of the hollow shaft formed by an assembly of said cathode elements.

15. A method for the electrolysis of electrolytic solutions which comprises the steps of introducing the solution to be electrolyzed into a plurality of superimposed horizontal, circular, rotating electrolytic cells at a point near the center thereof, introducing mercury into said cells at a point on the periphery thereof, withdrawing amalgam through slots in a hollow central drive shaft for said cells, and withdrawing gaseous products and depleted electrolytic solution from the periphery of said cells.

References Cited in the file of this patent UNITED STATES PATENTS 31 8,932 Trippe May 26, 1885 789,721 Decker May 16, 1905 1,569,606 Ashcroft Ian. 1 1926 FOREIGN PATENTS 10,925 Great Britain of 1900 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No,.. 2,951 026 August 30 1960 Georg Messner It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below'.

Column 4, line 42, for disposed read disclosed --e'.

Signed and sealed this 8th day of August 1961*.

(SEA L) Attest:

ERNEST W. SWIDER DAVID L. LADD I Attesting Officer Commissioner of Patents

Claims (1)

1. AN ELECTROLYTIC APPARATUS HAVING A MERCURY CATHODE, WHICH COMPRISES A HOLLOW ROTATING CYLINDRICAL SHAFT DISPOSED SUBSTANTIALLY VERTICALLY, A PLURALITY OF CIRCULAR PLATES ATTCHED TO SAID SHAFT EXTERNALLY ALONG ITS AXIS, ANODES AND SUPPORTING MEANS THEREFORE ABOVE EACH OF SAID PLATES, A SHELL ENCLOSING SAID SHAFT AND PLATES, MEANS IN SAID SHELL FOR INTRODUCING AN ELECTROLYTIC SOLUTION AND MERCURY ONTO EACH OF SAID PLATES, AND CONDUIT MEANS COMMUNICATING WITH SAID PLATES THROUGH SAID SHAFT FOR WITHDRAWING AMALGAM FROM EACH OF SAID PLATES.

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