US1971763A - Electrolytic cell - Google Patents

Description

Aug. 28, 1934. H. ALLEN ET AL 1,971,763

ELECTROLYTIC CELL Filed sept. 1s, 1928 Patented Aug. 2,8, 1934.

PATENT OFFICE .ELEoTRoLY'rIc CELL Herbert I. Allen and Douglas B. Ayerst, Portland, Maine, assignors to Electron Chemical Company, Portland, Maine, a corporation of Maine Application september 1s, 192s, serial No. 305,842 1o claims. (c1. 20d- 58) `This inventionl relates to electrolytic cells of that type in which a; portion at least of the anode chamber which contains the electrolyte is formed by a porous diaphragm. In such cells the daY 5 phragm overlies or lines a foraminous cathode and it has also been employed to serve as a gasket between the cathode and those portions of the cell which together with the' diaphragm form the l'anode chamber. In order to serve as a gasket a marginal portion of the diaphragm has been extended and compressed'between the cathode and the side walls and sometimes the end walls of the cell. We havejdiscover'ed that this construction isa source of hitherto unsuspected losses in effi- ,Q ciency, lack o'f purity of the desired products and length'of cell life. This margin being absorbent and being in contact with the cathode and in the current path, carries electrolytewhich is decomposed in the operation of the cell, but this not being ,where free percolation of the electrolyte through the diaphragm can take place to effect withdrawal of the decomposition products, results in such products contaminating the electrolyte and entering into further electrolytic reactions.

These result in side reaction products which not only decrease the eiiciency of the cell by substantial amounts, sometimes as muchas 5%, but cause impurities in thedesired decomposition products of the cell, and cause rapiddeteriora- 30 tion of the anodes.

'I'hese undesirable results may perhaps be lmore fully apparent by consideration of the specic action in a cell using brine as the electrolyte where caustic soda and chlorine are the desired products. When caustic soda, as-prcduced in thecertain other chlorine products. 'I'he higher the voltage reached by a cell when caustic soda is permitted to enter the anode chamber, the more these secondary reactions take place, and in those plantsA where a strong chlorine gas is required, it is customary to make frequent changes of diaphragm toprotect the anode andto keep the percentage of the carbon dioxide in the chlorine withinworkable limits.

In many types of cell the diaphragm, which is commonly asbestos, serves as the only gasket to prevent the electrolyte seeping between the free- 50 board or concrete body which forms 'the .gas chamber above the electrolyte and the cathode or the tank forming thecathode chamber, so' that unsightly leakages may also occur.

According to the present invention the diaphragm is so constructed that it is unable to present electrolyte in the path of the current, except where free percolation of the electrolyte therethrough is permitted. Likewise the cathode is constructed so as not to present current in the path ofthe electrolyte` except where free passage of current is desired. Free percolation of the electrolyte is,- of course, not possible within the joint between the cathode and free board or gas chamber above the electrolyte, and this invention has for a particular object to minimize losses in efliciency and anode deterioration due to side reactions which in previous constructions we have found to be present to a considerable extent in that portion of the cell. 'Ihis may be done by 80 so treating those parts of the diaphragm where free percolationis not possible either so as to renderthem non-porous so that they may contain no electrolyte or to insulate any electrolyte therein from the passage of electric current so that no electrolyzing action may take place therein, or by constructing the cathode so that the marginal or nonactive portions are thoroughly insulated, electrically, with some suitable insulating material or so that these marginal portions are constructed throughout of rubber, ebonite, bre or some non-conductor. In order thus to insulate these margins the material used must of course be impervious to water, brine and all other electroconductive constituents of the electrolyte, and in- 'ert to the products of electrolysis and of a cohesive'character such as rubber. By the use of such constructions not only is the efciency of the cell much increased but the frequent changes of diaphragm often resorted to where relatively l pure vchlorine is desired are made unnecessaryand thelife of the anodes will he prolonged by virtue of improved current distribution and the elimination of a current path of low resistance ordinarithe joint portions between cathode and anode 110 CII Cil

chambers of one type of electrolytic cell showing three different constructions which embody this invention, though it should be understood that the invention is applicable to any cell of the diaphragm type.

Figure 4 is a transverse vertical section toa smaller scale through a complete cell showing the joint construction shown in Figure 1.

Referring to the drawing, more particularly to Figures 1 and 4, 1 indicates a tank which is shown as provided with a reinforcing angle iron 2 which may be welded thereto along its upper margin.

` Depending within this tank is a foraminous cathode 3 having an outwardly turned margin 4 which may be extended at suitable points so as to form a lead as at .5 from a negative bus bar 6. As shown this marginal portion 4 overlies the horizontal upper leg 16 of the angle 2 and in order that a. liquid and gas tight joint may be effected therebetween, a gasket of rubber or other suitable material as at 7 is shown as interposed between the flange 16 and this margin. 'I'he margin 4 is preferably not foraminous, the openings through the tank extending substantially only up to the fold tline 8 between the margin 4 and the depending portion of the cathode.

Overlying the cathode is shown a porous diaphragm 10 which acts as a partition between the anode and cathode chambers, the cathode cham- I.ber being between this diaphragm and the walls of the tank 1 and the anode chamber being above the diaphragm 10 and being bounded also by the freeboard section 1l. This freeboard section commonly is provided with concrete side and top Iwalls 12 and 13, respectively, through the top fwall 13 of which extends the andes as at 14.

As shown in Figure 4 the anodes are arranged in two series which depend between pleats or folds in the cathode and diaphragm, in accordance with a construction shown and claimed in our application for patent Serial No. 120,421 filed July 13, 1926, for Electrolytic cells, although it will be evident that this invention is not limited to this particular type of cell.

As shown in Figures l and 4, the upper edge of the diaphragm 10 is outwardly turned to form a margin 20 extending between the margin 4 of the cathode and the lower face of the freeboard side walls 12. As heretofore commonly constructed this margin has been employed as a sealing gasket between the cathode andv freeboard section, but being porous the electrolyte has been drawn thereinto by capillary action in contact with the current carrying portion 4 of the cathode and in the path of curreitilow between the cathode and anode so that electrolysis of the electrolyte has occurred therein. As free percolation of electrolyte through the diaphragm at this point is impossible, since it is confined between the cathode and the freeboard wall section, the products of electrolysis have had no other escape than into the anode compartment and an interchange of electrolyte and the liquid products of electrolysis takes place by osmotic action with the diaphragm. As shown in Figures 1 and 4, however, this marginal portion of the diaphragm where free percolation of electrolyte therethrough is not possible, is protected in such a manner that electrolysis can not take place therein and as shown in these Figures this is done by enclosing this margin between the sides 22 and 23 of sheet insulating material folded about the edge of the diaphragm as at 24. This protective material must be a non-porous non-conductor of electricity in order to shut off the electrolyte in this margin from the path of current flow between the anode and cathode and it should also be resistant to the products of electrolysis. For example, in a cell for the electrolysis of brine for the production of caustic soda and chlorine it should be resistant to the action of the brine, caustic soda and chlorine and for this purpose rubber is quite satisfactory. Rubber in the form of what is known as tailors binding, which is a thin gum rubber, is quite satisfactory for the purpose. This gum rubber also serves as an effective gasket between the cathode margin and the freeboard section so that when the freeboard section is clamped down to the tank 1, as by means of the clamp comprising the threaded rods 30 engaging hooks 31 fixed to the sides of the tank and projecting through aclamping tie bar 32 at its top, the joint between the freeboard section, cathode and the tank may be made liquid and gas tight.

In Figure 2 a diierent construction is illustrated but for the same purpose. The margin 4 of the cathode 3 extends out between the upper margin of the tank 1 and the freeboard section 11, preferably between the gaskets 7 and 35, the gasket 35 being placed between the margin 4 and the freeboard section. The diaphragm 10 overlies .the forarninous portion of the cathode, as hereinbefore described, but its 'upper margin instead of being turned outwardly and extended beneath the freeboard section is shown as extended upwardly along the inner face of the freeboard section. This margin, above the point 40, in order to prevent it from containing electrolyte which cannot percolate freely therethrough, is then treated with some material which lls the pores thereof so that no electrolyte can be present. This material should be resistant to the products of electrolysis and be non-conductive, such as rubber. The rubber may be incorporated in this margin in the form of latex, either natural or artificial, and this also has* the further desirable characteristic of rendering this margin sufciently sticky so that it acts as a cement to fix the diaphragm margin to the inner face of the freeboard section.

Instead of extending the margin of the diaphragm upwardly along the inner face of the freeboardsection it may be impregnated with rubber or the like, as heretofore described, and turned outwardly beneath the freeboard section to serve in itself as a gasket between the cathode and freeboard section as is shown in Figure 3 where this impregnated margin is shown at 45. Where this is done the gasket 35 shown in Figure 2 may be dispensed with, the impregnated margin of the diaphragm performing the same sealing function. In order to effectually prevent the flow of electrolyzing current through the nonactive marginal portion of the diaphragm this portion must be protected from the passage of current not only from the cathode-but also from the wall of the freeboard or gas chamber because while the latter is ordinarily of non-conducting material, in use its surface is more or less coated with moisture, electrolyte materials and products of electrolysis, so that leakage therealong is bound to occur, which, if passed through this part of the diaphragm'is quite suicient to cause appreciable side reactions and anode deterioration. Thus substantially the entire surface of this marginalA portion should be protected by continuous insulation even if this margin is not rendered quite non-porous by insulation throughout.

been thus described it should be evident to those skilled in the art that various other changes and modifications might be made therein without departing from the spirit or scope of this invention as defined by the appended claims.

We claim:

1. An electrolytic cell for electrolyzing brine, comprising a tank, a foraminous cathode depending within said tank and having an outwardly turned margin supported by the upper edge of said tank, a freeboard section supported by said margin, means for sealing the joint between said tank. margin and section, and a porous diaphragm overlying said cathode, said diaphragm having its margin extending above said joint, said extended portion being impregnated with a non-absorbent non-conducting material resistant to chlorine.

2. An electrolytic cell for electrolyzing brine, comprising a tank, a foraminous cathode depending within said tank and having an outwardly turned margin supported by the upper edge of said tank, a freeboard section supported by said margin, means for sealing the joint between said tank, margin and section, and a porous diaphragm overlying said cathode, said diaphragm having its'margin extending above .said joint and xed to the inner face of said ffreeboard section.

` 3. An electrolytic cell for electrolyzing brine, comprising a tank, a foraminous cathode depending within said tankland having an outwardly turned margin supported by the upper edge of said tank, a freeboard section supported by said margin, means for sealing the joint between said tank, margin and section, and a porous diaphragm overlying said cathode, said diaphragm having its margin extending above said joint impregnated with rubber and fixed to the inner face of said freeboard section.

4.,An alkali and chlorine electrolytic cell having a gas chamber, a foraminous cathode jointed to said gas chamber and extended therebelow, a porous diaphragm4 overlying said cathode and having its margin extending into said joint, and a continuous non-porous U shaped layer of insulating material engaging about the edge of said diaphragm and between said cathode and diaphragm and said chamber andndiaphragm.

5. An electrolytic cell having "a gas chamber, a foraminous cathode jointed to said chamber and extended therebelow, and a porous diaphragm overlying the inner face of said cathode and xed to the inner face of said chamber above said joint.

6. An electrolytic cell having a gas chamber, a n

overlying the inner face of said cathode and fixed to the inner face of said chamber above said joint and insulated therefrom.

7. An alkali and chlorine cell comprising a tank, a foraminous cathode depending within said tank and having an outwardly'turned margin supported on the upper edge of said tank, a freeboard section supported by said margin, an anode depending from the freeboard section adjacent to said cathode, and a porous diaphragm overlying 'said cathode and having its margin above said cathode impregnated with rubber and rendered thereby impervious to electro-conductive constituents of 'the electrolyte.

8. An alkali and' chlorine cell comprising a tank, a foraminous cathode depending within said tank and having an outwardly turned margin supported on the upper edge of said tank, a freeboard section supported by said margin, an anode depending from the freeboard section adjacent t`o said cathode, and a porous diaphragm overlying said .cathode and extending into the joint between said tank and freeboard section, said extending portion being impregnated with rubber and rendered thereby impervious to electroconductive constituents of the electrolyte.

9. An alkali and chlorine electrolytic cell comprising a tank, a foraminous cathode within said tank and having'an outwardly turned margin supported on the upper edge of said tank, a porous diaphragm overlying said cathode and having its margin above said cathode impregnated with a non-conducting agent having the cohesive characteristics of rubber and resistant to the products of electrolysis and rendering said margin impervious to electro-conductive constituents `foraminous cathode jointed to said chamber and yextended therebelow, and a porous diaphragm of the electrolyte by completely filling the pores of the diaphragm margin. l

10. An alkali and chlorine electrolytic cell having a gas chamber, a foraminous cathode jointed to said chamber and extended therebelow, a porous diaphragm overlying said cathode and extended above the lower edge of said joint, a nonporous insulating medium having the cohesive characteristicsy of rubber and impervious to the electro-conductive constituents of the electrolyte carried by said extended portion and insulating substantially the entire surface thereof against passage of an electrolyzing current, andan anode depending through said gas chamber adjacent to said cathode. f HERBERT I. ALLEN.

- DOUGLAS B. AYERST. l

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