US2154830A - Electrolytic cell - Google Patents

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April 8, 1939. F. BENCKER 2,154,830

ELECTROLYTIC CELL Filed June 16, 1935 Patented Apr. 18, 1939 UNITED STATES 2.154.830 nmc'rnomrnc can.

. Franz Bencker, Leverknsen-I. G. Wei-k, Germany,

assignmto I, G. Farbenindustrie Aktiengesell- 'schaft, Frankfort-on-the-Main, Germany Application June 16, 1933, Serial No. 676,171

' In Germany July 19, 1932 3 Claims. (01. ant-5a) The present invention relates to improvements in electrolytic cells in which the cathode consists of mercury, .which cells are commonly used for preparing alkali metal amalgam from alkali metal chlorides.

The bottom of an electrolytic cell covered with mercury serving as the cathode calls for great precautions. It must be tight against mercury and perfectly even, it must be unattackable by .10 the electrolyte and its decomposition products and must be sufllciently strong so that sagging is impossible.

The material used heretofore was first of all concrete or ferro-concrete. 1 But also the amall 5 gamcellswere made of wrought-iron tubs, which on the inside were lined with tiles or cement, since unprotected metal; according to the experiences made so far, was out of question. Also ceramic materials or natural stones were used for these cells." But the above-named conditions were only partly achieved with these constructions, which were not at alldurable and caused considerable expenses. Thus, for instance, cement or concrete undergo adeep decomposition and destruction by the attack of the concentrated alkali lye, which is always present between the amalgam and the bottom of the cell, which causes the more or less deep penetration of the mercury into the-concrete and also causes losses J of mercury. Further, all these cells no matter how they are constructed have the disadvantage to. render the placing of the current cables to the cathode difficult. For this-purpose it is necessary to pierce the bottom -o the cell at various places and cunder these conditions it is, of course, rather difficult to keep the bottom of the cell tight. against mercury. The current connections made in this manner have the disadvantage that ,on account of their small surface, caused by the difllculty of placing them, crusts are formed whereby a bad current conduction and therewith loss of voltage is brought about. They cannot be cleaned without interrupting the working in the cell and even then the purification is imperfect.

It has been found that all these disadvantages can be overcome and that a bottom complying with all the above indicated requirements and solving the problem of current supplyin the most simple, most safe and cheapest manner can be obtained when shaping the cell as a trough consisting of a metal which is unattackable by the electrolyte, its decomposition products and mercury, for instance, iron, the walls of which are provided with a lining which is to protect the walls against the attack of the electrolyte and its. decomposition products and which at the same time serves as electric insulator. This lining may consist, for instance, of rubber, chlorinated rubber, Bakelite, etc. cell, however, as far as it is covered with mercury, is not covered with this lining, so that a bright metal surface remains. it is a surprising fact that these bright metal surfaces do not cause any working interruption and do not diminish the safety of the cell, provided, of course, that 'while working in the cell is performed these surfaces are constantly covered with the mercury. It was surprising to ascertainthat such great surfaces serving as current conduction. for the mercury do not cause the formation of crusts and thus offer an unobjectionable current conduction to the cathode, since small parts of crusts after having attained a certain size are thrust out automatically. Thus a constant automatic purification of the current conducting surface occurs which causes a very favorable electric tension of-thecell.

The construction of such mercury cell may be carried out especially simple and cheap when starting with level positioned iron U- and I-pieces. Thereby all the conditions referred to above, 1. e. impermeability of, the mercury, even and nonsagging bottom, chemical and mechanical strength are accomplished. The minus pole is merely attached to the U- and I-pieces and thus provides for a very cheap, very simple and safe distribution of the current over the whole cathode.

The U- and I-pieces offer many more advantages to the construction of the mercury cell. Thereby it becomes possible to keep the temperature of the cathode and therewith of the whole cell within the desired temperature ranges with very simple means. It is only necessary to provide for pipes or similar appliances at the outside of the cell, for instance, by welding on pipes through which heat exchanging means, say for instance a cooling liquid or also a heat conductor may be led. Further, by employing U- and I- pieces the mercury cell can be'constructed very simply, sothat a purification of the electrolytic cell itself will be rendered unnecessary. By welding in walls it is possible to easily provide for separate chambers at both ends of the cell which take up the impurities taken away with the mercury, for instance, coarse graphite particles. of the cell at any time without any interruption of working in the cell.

The bottom of the The separating chambers allow cleaning struction illustrative of the principles of the pr ent invention; and

Fig. 2 is a transverse sectional view or the same cell.

Figure I illustrates a longitudinal section, Figure 11 illustrates a cross section. Numeral I is an I-piece with welded in head-walls 2. The whole cell is surrounded by a welded flat iron frame 3, into which the cover 4 is tightly placed by means of putty or another tightening means. The anodes 6 with their current supplies 5 are attached to the cover 4. The mercury enters the cell by pipe I, flows along the bottom of the cell and leaves the cell by pipe 8. The separating chamber 9 forms a syphon by means of which impurities of the mercury are retained. The partition Ill forms the separating wall between electrolytic chamber and the adjacent separating chamber. The solution enters at the inlet II and fills the cell almost up to the lid. Thereby the' accumulation of explosive gases being eventually produced in the cell is reduced to a minimum so that the cell is rendered practically safe against explosions. The height of the solution is determined by the height of the movable overflow pipe l2. Through this overflow pipe i2 the solution leaves the cell together with the gases formed. The metallic inside of the cell with the exception of the bottom covered with mercury is provided with a lining l3 which protects the cell from corrosion and whichis electrically insulating. The cell is deposited on supports ll, whereby the rapidity of the mercury flow can be regulated. It is ad- 'visable to place two of these troughs one beside the other when the alkali metal hydroxide solution is to be prepared by electrolizing an alkali metal chloride solution, whereby alkali metal amalgam is produced at the cathode. In this case the mercury enters andpasses through the first trough whereby it is converted into alkali metal amalgam and flows back through the .second trough wherein the alkali metal amalgam is decomposed with water" while forming alkali metal hydroxide solution. Thus the contact between cell and decomposer is reduced'to a minimum.

Iclaim:- v

1. In an electrolytic cell working with-a mercury cathode, the arrangement of a level positioned iron piece selected from the group consisting of U- and'I-pieces being provided with head-walls, the inner walls of the said trough being provided with a lining which protects the walls of the cell against the attack of the decomposition products of the electrolyte and at the same time serves as electric insulator, the bright iron bottom of the cell covered with mercury serving in its whole dimension as current supply of the cathode.

2. In an electrolytic cell working with a mercury cathode, the arrangement of a level positioned iron U-piece being provided with headwalls, the inner walls of the said trough being providedwith a lining which protects the walls of the cell against the attack of the decomposition products of the electrolyte and at the same time serves as electric insulator, the bright iron bottom of the cell covered with mercury serving in its whole dimension as current supply of the cathode.

-3. In an electrolytic cell working with -a mercury cathode, the arrangement of a level-positioned I-piece being provided with head-walls, the inner walls of the saidtrough being provided with a lining which protects the walls of the cell against the attack of the decomposition products of the electrolyte and at the same time serves as electric insulator, the bright iron bottom oi the cell covered with mercury serving in its whole dimension as current supply of the cathode.

FRANZ BENCKER-"I

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