US2508523A

US2508523A - Device for the protection of the cathodes of electrolytic cells

Info

Publication number: US2508523A
Application number: US696066A
Authority: US
Inventors: Krebs Eduard
Original assignee: Krebs and Co AG
Current assignee: Krebs and Co AG
Priority date: 1946-09-11
Filing date: 1946-09-11
Publication date: 1950-05-23
Anticipated expiration: 1967-05-23

Description

M y 3, 1950 E. KREBS DEVICE FOR THE PROTECTION OF THE CATHODES I OF ELECTROLYTIC CELLS Filed Sept. 11, 1946 s 1 4% 1 W 40 J fm emor Zia/4 90 Km? Patented May 23, 1950 DEVICE FOR THE PROTECTION OF THE CATHODES OF ELECTROLYTIC CELLS Eduard Krebs, N euilly-sur-Seine, France, assignor to Krebs & 00., Zurich, Switzerland, a body corporate of Switzerland Application September 11, 1946, Serial No. 696,066

1 Claim. 1

This invention relates to a device for protecting the cathodes in electrolytic cells as used for decomposing alkaline chlorides.

It is known that in some such cells, the oathode is constituted by a metal in the liquid phase, generally mercury, flowing on a fixed iron cathode, and is continuously renewed under a layer of brine constituted by a solution of the chloride which is being subjected to decomposition. Such mercury, as the electrolysis proceeds is converted into an amalgam which is at a later time decomposed in another stage.

In such installations there are generally a plurality of cells disposed in series, and it is possible if the need therefor arises (such as for cleaning, maintenance and the like) to stop the operation of any one or ones of them without thereby holding up the plant as a whole; suchresult is obtained by short circulting the anodes and the cathode of one or of several cells, which has for effect to bring the anodes and the cathode to the same electric potential and breaks the flow of the electrolysis current in the desired cell or cells.

Such interruption however offers serious drawbacks, the principal ones of which are the following:

First of all, the metal forming the liquid cath- V ode is exposed to chlorination by reason of the presence of free chlorine dissolved in the brine which coats the cathode, and if the circulation of the liquid cathode is stopped, such chlorination occurs on the fixed iron cathode as the latter is exposed by the flow of the liquid cathode. The chlorination of the liquid cathode produces a, substance detrimental to the proper operation of the cell, and in the majority of cases the mercury constituting said cathode should be replaced, at the time the plant is put once more into operation, by pure mercury.

Then, chlorination of the fixed cathode entails grave defects: it gives rise, in operation of the cell, to an additional resistance to the passing of electric current and furthermore causes troublesome obstacles for the cycling of mercury and for a proper distribution or spreading thereof over the entire surface of said fixed cathode. A further detrimental result is the frequent production of local decomposition of the amalgam with resulting formation of hypochlorite and release of hydrogen which mixes with the chlorine resulting from the decomposition of the treated chloride, and the net result is the production of impure chlorine.

Moreover during said attack of the fixed cathode there is formed on the surface of the latter 2 not only iron chloride but also iron oxide, both products very difficult to remove. However, in the course of the process, they do finally become gradually carried away by the liquid circulating cathode; this results in the introduction of iron,

amalgam into the amalgam-decomposing apparatus and the cathode product, which is generally very pure, is thereby contaminated.

In order to avoid the various above drawbacks, the brine contained in thecell is generally evacuated upon stopping; this of course entails replacing fresh brine into the cell when the latter is again connected up into the electric circuit,

which constitutes a troublesome constraint. Said drawbacks may also be avoidedat least in part by introducing into the brine in the cell, on stopping, an alkaline solution made up of the hydrate of the alkaline metal being treated, this being done in order to cause the totality of the chlorine I dissolved in the brine to combine so as to reduce the tendency of the cathode to become chlorinated, but when this is done hypochlorite is formed which will later have to be eliminated from the circulating brine.

The present invention has for its object to make possible the stopping of one or more mercury cathode cells in a given installation by short circuiting said cells, the remaining cells continuing to operate and that being true without it being necessary to take any special precautions either on stopping or on restarting, all the drawbacks usually encountered being at the same time avoided.

It is known on the other hand that if during a, halt, a difference of potential is maintained in the cell by any suitable means, so as to determine in said cell the flow of an electric current, the intensity of which may be very small with respect to that of, the electrolysis current and insufiicient to cause any substantial electrolysis effects, said current having the same direction of flow as the electrolysis current and also terminating in the cathode of thecell, the polarization of the cell being maintained, none of the above-mentioned drawbacks will occur. In order to restart it is only necessary after having started the cycling of the mercury, to re-establish the electrolysis current between the anodes and the cathode of said cell; however, inasmuch as the stopping of one or more cells has been effected by a short circuit which puts the anodes and the cathode of a given cell at the same electric potential, it will be seen that it is not possible to use, in order to cause the flow of said current which may be termed protection current all or ber of cells of the installation being capable of being simultaneously subjected to the protec tion current and withdrawn from the action of the electrolysis current, the two latter operations being in practice carried out successively (absolute simultaneousness being of course impossible to accomplish), and being therefore separated by a certain lapse of time, which lapse is then advantageously reduced to a minimum, and the application to the cell of the protection. current being preierabl-yeffected before the sup.-... pression of the. electrolysis current, this. being done inorder to ensure the factthat at all times an electric current, whether a protection or an electrolysis current, will not fail to traverse the cell or cells in question, whereas during such stop, the-remainder of the cellsof the plant may continue to be supplied with electrolysis current. and operate in normal conditions.

' The protection current having a very low inten sity, theauxiliary anodes" through which said current is led'in may be ofrelatively very small cross-section, which makes both for low cost and reduced" cumbersomeness ofsaid' anodes, and thesame'w'ill'ofcourse bearranged injudiciously se lected' numbers invarious suitable locations in each cell; 7

It will be understood that it is then merely necessary, when a cell is short-circuited and consequently stops operating, to-connect the auxiliaryanodes and the cathode of; said cell to any source of direct electric current under suitable tension, in order-to maintain said cell polarized and avoid all the drawbacks which will result from the interrupti'on thereof. 7

When the cell: has been stopped and placed under the actionof the protection current itmay then be submitted to any desired operation and in particular cleaned. r 7

As stated above, the electrolysis effects-produced by the electrical protection supply of current arepractically negligible; they only bring about an excessively low quantity of evolved chlorine. However, if it' is desired completely-to prevent such evolutionof chlorine it will only'benecessar-y- :to introduce intothe cell, upon stopping, a quan Y taneously to stop one or moreor even the entirety of the cells. of a given: installation, while maintaining the same under a protection current.

The'accompanying drawings illustrate aform j ofembodiment of the invention; it will of course be understood that. thisv embodiment is given merely by way.- of" illustration'and; with nointen- 7 tion of limiting the scope. of the invention, since other devices could be constructed depending on the particular type of electrolysis elements to which it may be contemplated to apply the invention.

In the drawings, there is diagrammatically i1- lustrated an electrolysis element or cell of the type comprising an elongated tank; wherein anodes extend throughoutthe entire length of the cell. The bottom of said tank, which serves the function of a fixed cathode, is slightly inclined so as to provide for the outflow of the mercury which terms" the liquid cathode. 'Said tank is so constructed that the side walls thereof are electrically insulated with respect both to the bottom and the mercury, which both act as cathodes. In operation, the mercury, while flowing through the cell becomes, oaded, With the metal produced by 7 the walls, but. furtherat': the points where the tional area and are, forinst'anoe, constituted byanodes; extend through said. covers, in such a. way: that, the. chlorine sewerated.hr electrolysis in. s.- eouscondition may'notspread. outinto the atmosphere, of the premises wherein. the cell. is installed;

FigureI is anzelevational view in. longitudinal section on. line A-i-A" of Figure II; of an electrolysis cell; v

Figure II is a, planview of the same cell, the sealing covers being: removed;

Figure III is: a transverse section on. Ba-B of. Figure-Ill of an installation inoludinga plurality of electrolytic cell's, illustrating the method used for connecting up: said. cells in series, the num.-. ber of cells being limited only by the voltage selected for the direct'electrolys is current.

According tothe-present embodiment, the electrolysi'sfcurrent flows from electrolysis anode I to thefixed cathode 2, the mercurywhich forms the fluid cathodeentering at'landleaving the cell at 5. The brine to bedecomposedis shown at 6; it

flows into the cell at 1 and out at 8. The chlorinegenerated by electrolysis leaves the-cellat9. The

circuit connections for conducting theelectrolysis current are shown'at i0, and the numeral I l indicatesswitches which are operative-when closed, to short-circuit each individual cell independently of all the others, and thus to remove it from the effect of the electrolysis current.

The'aux-iliary anod'es such as: I2, theobject-of' which; accordingto theinvent-ion, is to-supply the cell with protectioncurrent, are of small secrods of graphite-ofa diameter of about 1'0 millimeters. They are arran'ged along the-cell, spaced from one another by a distancewhich, in the present example, is about onetcntwo meters. number thereof in: each cell is therefore small.

Inasmuch as said auxiliary anodesare located very close to theelectrolysis anodes; it maybe de-- sirable to enclose-them within a l-insulated sheath-- made of ebonite, for example, in: order that the pathof the protectioncurrent may connect with the cathode only at the base of said auxiliary anodes, and not throughtheir sides passing through the electrolysi's anodes. The protection currentfor each. cell: is supplied through lines I3.

Theseprotection currentinlets are supplied, in-

dividually for each cell, with direct'current whichmay be'derived: from an auxiliarysource of any The.

aooaoas auxiliary generator unit, a rectifier supplied with A. 0., etc.

The above described device operates as follows: when it is desired to stop oneor several, or even the totalityof the cells in the installation, the line 13 of such cell or cells is connected to the protection current supply by any suitable means such as a switch or contact plug, then the switch ll of each cell to be cut off is closed. The shorting of such cell or cells is thus effected without any of the cells switched out of the path of flow of the electrolysis current being at any time deprived of either protection or electrolysis current. The protection current enters each cell by way of the auxiliary anodes and leaves said cell through the fixed cathode.

In any case, neither the fixed nor the fluid cathode will be subject to the above mentioned drawbacks, the bias or polarizing voltage of the cell being at all times maintained.

When it is desired to resume operation, it is simply necessary to open the switches H and thereafter to cut off the supply of the auxiliary protection current or currents.

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

An apparatus for producing the electrolytic decomposition of an alkaline chloride comprising a plurality of electrolytic cells connected in series each including cathode means, main anode means, auxiliary anode means, a main current supply means for said apparatus, an auxiliary relatively low current supply means for said apparatus, means for connecting said cathode and said main anode means in series with each other and with said main current supply means whereby relatively high current may flow through said cells producing therein said electrolytic decomposition, means for short circuiting said cathode and said main anode means individually in each cell, and means for individually connecting said cathode and. said auxiliary anode means in each cell with said auxiliary current supply means whereby relatively low current may be circulated through each of said cells producing therein substantially no electrolytic decomposition, whereby it is possibie to stop operation of any of said cells severally or in combination in said apparatus while maintaining a flow of relatively low non-electrolysing current through each of said non-operating cells.

EDUARD KREBS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 918,370 Rink Apr. 13, 1909 1,265,551 Thomson May 7, 1918 FOREIGN PATENTS Number Country Date 1,661 Great Britain of 1893