US3354072A - Electrolytic cell having vertically disposed electrodes - Google Patents

Description

S. T. GLOVER 4 Sheets-Sheet l NOV. 2l, 1967 ELECTROLYTIC CELL HAVING VERTICALLY DIsPosED ELECTRODE'S Filed July 18, 1963 S- T. GLOVER 4 Sheets-Sheet 2 Affi/Vif ELECTROLYTIC CELL HAVING VERTICALLY' DISPOSED ELECTRODES Nov. 21, 1967 Filed July 18, 196s Nov. 21, 1967 l s. T. @LOVER 3,354,072

ELECTROLYTIC CELL HAVING. VERTICLLY DISPOSED ELECTRODES 4 Sheets-Sheet 3 Filed July 18, 1963 s. T. GLovL-:R 3,354,072 ELECTROLYTIC CELL HAVING VER'IISALLY` D ISPOSED ELECTRODES Nav. 21, 1967 4 Sheets-Sheet 4 Filed July 18, 1963v United States Patent Office 3,354,072 Patented Nov. 21, 1967 3,354,072 ELECTROLYTIC CELL HAVING VERTICALLY DISPOSED ELECTRODES Sidney Thomas Glover, Runcorn Heath, England, assignor to Imperial Chemical Industries Limited, London, England. a corporation of Great Britain Filed `Iuly 18, 1963, Ser. No. 295.929 Claims priority, application Great Britain, July 18, 1962, 27,610/ 62 3 Claims. (Cl. 204-219) This invention relates to an electrolytic cell, more particularly for the manufacture of chlorine and caustic alkali by electrolysis of brine using a moving mercury cathode.

It is a well-established practice to electrolyze brines in cells having a moving mercury cathode. It has hitherto been found mostl satisfactory to use flowing mercury cathodes which are substantially horizontal, as such an arrangement minimizes the problem of maintaining a continuous unbroken mercury surface during electrolysis. This continuity of the mercury surface is especially important in cells in which the mercury covers an iron support, since exposure of the iron to the electrolyte results in hydrogen evolution and corrosion. These horizontal cells have the disadvantage, however, of occupying an undesirably large floor area.

Attempts have been made to construct cells in which the mercury cathode film ows in a substantially vertical 01' steeply inclined direction since such cells have many inherent advantages, including particularly flexibility in operation and economy of yfloor space and mercury usage. The operating difficulties so far associated with these vertical cells have been even greater than those associated with the generally favoured horizontal cells, and these inherent advantages have not been enough to compensate for the additional disadvantages. In particular, it has been found that it is very diiiicult to maintain the anode-cathode spacing within the narrow range which gives satisfactory roperating eiciency, because of wear and erosion of the conventional anode materials such as graphite.

Consequently no overall advantage has hitherto been found for vertical cells.

I have now found, however, that the advantages of a vertically disposed cell for the electrolysis of brines can be obtained economically an-d reliably when the anode is made of titanium having a platinum metal coating thereon. The wear-resistant nature of platinized titanium, I find, makes it possible to assemble afvertical cell having an inter-electrode gap which can be 'maintained substantially uniform throughout the structure and over a period of use.

Thus according to my invention I provide an electrolytic cell for the manufacture of chlorine by e'ectrolysis of brines, having a vertically disposed cathode support provided with a flowing mercury cathode film thereon an-d an adjacent, substantially parallel anode comprising titanium having a coating of a platinum metal on the surface thereof.

`For the purposes of this invention, the term vertically disposed includes not only those arrangements in which the electrodes are strictly vertical, but also those in which the electrodes are inclined to the vertical to a minor extent. The angle of inclination to the vertical is preferably not very great, however, as the advantages of the vertical type of cell would then be lost or considerably reduced. In general, the angle of inclination should not be greater than about 30 to the vertical, though in some forms of apparatus less departure from the vertical than this can be allowed. It is important, for example, that the slope of the cathode surface should not cause diiculties in maintaining the mercury film and in particular should not cause the mercury to fall away from the supporting top surface. For this reason, an overhanging cathode support, if used, should usually be limited in slope to an inclination not greater than about 10 from the vertical.

The cathode support may be hollow or solid, but should be strong enough to withstand the pressures of brine and mercury employed and should preferably have a sufH- cient electrical conductivity for it to serve as a means for conducting the electrolyzing current to the mercury cathode. Convenient materials for this purpose are metals, especially iron or mild steel. A hollow cathode support has the advantage of allowing the mercury supply to be fed through it.

It is also very desirable that the outer surface of the cathode support should be made of a material upon which the mercury readily wets the surfaces and forms a satisfactory film, or that the outer surface of the support should be treated so as to achieve this. When the support is made of iron or steel, this effect can be secured by usingrmercury in which a small proportion of alkali metal is dissolved. Even a trace of sodium, for example 0.01% by weight by weight or less in the mercury will be sufficient to achieve this effect.

The mercury cathode film can be obtained by feeding a supply of mercury to the top of the cathode support and allowing it to flow down the cathode support. A weir or other distributing device may be used to spread the mercury and secure a suitably extensive and steadily flowing film. The mercury supply is most conveniently obtained by a recirculation system in which mercury which has passed through the cell is treated in conventional manner for recovery of its alkali metal content and the recovered mercury is returned to the cell.

The supply of mercury is preferably carried out by forming a pool of mercury in a suitable cavity at the of the cathode support, and allowing the mercury to overflow from this pool down the surface of the cathode support. The mercury may be fed to the pool in anyv convenient manner, for example from an overhead supply pipe or by making the cathode support hollow and feeding the mercury upwards through it. It is preferred that the mercury feed should disturb the surface of the pool as little as possible so as to facilitate a smooth liow of mercury in the cathode film.

The anode structure may be made of titanium in any convenient form, providedpwith an operative anode surface consisting of a lm of a platinum metal. The titanium may be the pure metal or an alloy. For economy of material it is preferred that the anode should be made of thin titanium sheet which may be supported as necessary by struts or other supporting members. The sheet may be pierced, slotted, expanded, or the like or may be replaced by a woven titanium wire gauze. An especially suitable material is the so-called expanded metal sheet which is made by cutting a large number of slots in a sheet of the metal .and then stretching the sheet and, optionally, rolling the resulting metal mesh to flatten it.

The platinum metal may be deposited on the titanium surface by known techniques, for example by electrodepo-l 0r by coating with a platinum-bear-l ing paint and tiring as in the ceramic industry. The par-r sition or sputtering,

production 1capacity .required.orhthesmaterials available. v

The simplest possible form consists of one or more pairs of substantially parallel planar surfaces; this form, which mayconveniently .he termed a plate form, has the iadvantage Aof'being .more compact than-other forms and lso is more economical .of space.

`Arnespecia'lly useful formisthat in which oneelectrode surface vis disposed .around the other. rThis -is -done yvery conveniently .by .making Ythe Velectrode surfaces of tubular form and mounting .them coaxially,.one within ythe other. The inner electrode may .be solidor hollow, but in either case itpresents an equivalent operativesurface. The tubular electrodes maybe of any convenient .cross section, having straight or carved surfaces or a combination of these, as for example circular, elliptical, polygonal (for example rectangular or hexagonal.) or that of a partially or completely flattened tube. This coaxial arrangement has the advantage of reducing theproblem of maintaining an adequate uniformity, continuity or spread .of mercury cathode film, by avoiding vertical edges on the cathode support surface. A cathode support surface Vhaving .a cross-section which is lfree from abruptly angular .portions '(i.e. issubstantially curved throughout) is especially useful in this respect. Tubular electrodes of substantially circular `cross-'section are preferred, however., as they are particularly easy to fabricate and assemble with the `desired accuracy, "and 'enable a substantially uniform interelectrode "gap and 'electrolyz'ing current distribution to be achieved. A plurality of pairs of coaxially arranged pairs of tubular electrodes can be used if desired, and these can be assembled in any 'convenient spatial arrangement, for example vin honeycomb fashion. Appropriate electrical connections, 'for 4example by way vof structural links, can be made lbetween the various electrode surfaces. The owing mercury cathode film vmay be provided on either the outer or the inner tubular 'surface of the pair; in general, I prefer that this mercury iilrn sshould be on the innerione in 'single -pair assemblies 'and on the outer ones in lmultiple ypair assemblies.

'The -anode may be continuous or pierced by holes. When the `anode is in la form having holes 'through its thickness, the lplatinum metal may be deposited lon the side -remote from the vcathode 'or on the side adjacent to the cathode. When on `the adjacent side of the anode, the 'current efficiency `will oe greatest, but the chlorine evolved may block "the rinter-electrode j'gap 'sufficiently to hinder operation of the cell, particularly'when the rate o'f brine feed is slow'or -the anode is 'n'otlouvred in order to facilitate ithe 'escape of the chlorine. When Von the remote side Aof the anode, vthe Vplatinum Ametal still functions efliciently 'as an anode and the `chlorine evolved, being already'outs'ide ofthe inter-electrode gap, 'readily escapes with "the minimum interference in the operation 'of the cell. The titanium metal, being itself inoperative as an anode surface inthe brine, does'notprevent operation of the platinum metal vsurface as 'an anode even though the platinum metal is at a 4greater "distancefromthe cathode than sthe titanium 'part of rthe structure.

When 1the anode is ina 'form 'having holes through its thickness, the brine "can be *fed at 'a relatively slow rate, and 'the chlorine gas which lis Vevolved at the anode can be deflected Yaway from the int'erelectrode gap kby 'suitable shaping ofthe anode, 'for example by forming each aperture iin the 'anode las a louvre. 'The direction of slope of the louvre lwhich is most effective will depend upon the particular brine `flow used. The coniiguration which is better rsuited to the particular rates yof brine *flow and gas evolution in Iindividual cases can, however, be readily found by simple trial.

'The brine for use in the ycells of the present invention are essentially aqueous Asolutions of alkali metal chlorides particularly sodium chloride 'and/ or potassium chloride, optionally 'containing small proportions of other compounds and may be for vexample natural brines which may have been treated to remove undesirable constituents b..-

for electrolysis, and 4includes `recovered `and/ or "partially used brines.

The flow of brine through the cell should be directed primarily through the verticalspace defined by the anode and cathode, though it need not lne-confined to this space alone. When the anode is made of sheet material, free from any holes, the brine .flow is preferably confined between the anode and cathode and a high brine velocity is used to prevent accumulation of chlorine in the anodecathode space and consequent interference with the electrolysis. This form of cell is very suitable for the electrolysis of depleted (i.e. partially spen) brines, and lends itself to an especially simple design 'in which a tubular cell is provided with copper bands at intervals along its length for `the vsupply of electrolysing current. The flow of brine may bein an upward or downward direction, 'though inthe high-speed, 'confined ow cells, this is preferably downward.

Entry of brine and mercury, and removal of electrolyzed brine, amalgam and chlorine `can be `affected through vconventional piping, separators, seals and other ancillary apparatus in conventional manner. Also, tbody members of thecell, other than l'those rnade'of"titanium,l

can be 'made of 'conventional materials, for example concrete, lrubber-covered steel, and the like. t

'The anode-'cathode spacing may be determined, -as is conventional in the art, having regard for such factors as ypowerc-onsumption andthe particular cell and operating conditions employed. Usually a gap of up to 10 mm. is employed.

Unlike the conventional graphite anodes which "wear away -quite rapidly, Va platinized titanium anode does not wear suicientlyduring use to make 'frequent adjustment necessary. IWhen the -c'ell of the present `invention employs vertical electrodes, `and especially `when one of the electrodes also surrounds lthe 'other electrode completely, there Vis practically `no opportunity for adjusting the interelectro'de gap once the 'cell has been assembled. Assembly can be l'carried out vhy 'careful measurement and Vcalculation, but "even so it is very desirable in some instances that 'thereshould'he some `provision for minor adjustment of .an assembled cell when yit is =rst put into service, -so that the maximum operating eflici'ency can be secured. This problem of yadjustment isespecially diicultto solve for cells in which the anode and the 'flowing mercury cathode are substantially vertical, since any 'adjustment offtheinter-electrode gap requires Jmovementin a substantially horizontal direction. :In a ycell having horizontal electrodes, itis 'common Vfor adjustment Yto be made by movement of -the upper electrode directly away from the other A'by-means yof 'an adjustable support passing through the `roof of 1the cel1,but this simple technique vcannot be adapted vdirectlyto vertical cells because-the electrode support would then have to pass through the cell wall below the 4brin'e surface and the problems of sealing would lbe very considerable. Moreover, the Vadjustment 'of the gap would not '.be uniform over the .whole 'operative surface of the electrodes unless Aflat `electrodes wereused.

:I 'have falso found -that 2the desired degree 'of-adjustment can ,readily be secured when the `anode and 'cathode 'surfaces are made substantially parallel to each other and inclined y"to the vertical, and a means "is providedor adjustment of the relative spacing 'of the two electrodes in a Asubsta'ntially vertical direction.

Adjustment ofthe lrelative spacing of the two electrodes in a vertical vdirection then results in a -variation of 'the inter-electrode gap, the magnitude 'of Vwhich will 'depend of inter-electrode gap. The means for adjustment of the relative spacing of the electrodes can be any convenient` device for providing the desired degree of movement, for example a screw-actuated device, and the position at which the upper electrode support (usually the anode support) passes through the lid or cover of the cell can be sealed by any of the conventional sealing devices to ensure that undesired leakage of chlorine and/or brine electrolyte is kept as low as possible.

The invention is illustrated but not limited by the following drawings wherein FIGURE 1 represents a transverse vertical section of an electrolytic cell having concen tric cylindrical anode and cathode; FIGURE 2 represents a transverse vertical section of an electrolytic cell similar to that in FIGURE 1 but in which the brine electrolyte is confined entirely between the anode and cathode during electrolysis, and which is primarily intended to utilise a high rate of flow of electrolyte through the inter-electrode gap; FIGURE 3 represents a transverse vertical section of an electrolytic cell similar to that of FIGURE 1 but having coaXially arranged anode and cathode, each being in the form of a frustum of a cone; FIGURE 4 represents a transverse vertical section of an electrolytic cell in which the cathode support is in the form of a plate interp-osed between two sheet -anodes; and FIGURE 5 is a diagrammatic drawing, in transverse vertical section, of a multiple cell based on the various unit cells described above and particularly that of FIGURE 4. The drawings are not to scale. In FIGURE 1 the cell comprises a base plate 1 to which are secured cylindrical cathode support 2 and outer wall 3. Through the base plate 1 and within the hollow cathode support 2, an inlet pipe 4 is provided which passes upwardly to a barrier plate 5 which seals the whole of the inner cavity of the cathode support 2 near its upper end. The mercury supply 6 is fed through this inlet pipe 4, and forms a shallow pool 7 from which the mercury overflows, across the upper edge 8 of the cathode support 2 to form a thin flowing film of mercury 9 on the outer surfaoe of the cathode support 2, and then collects in another pool 10 from which it is run otr through outlet pipe 11.

Surrounding the cathode support 2 and the mercury film 9 flowing on its surface, is an anode 14 consisting of a cylinder of platinized titanium metal sheet, gauze or expanded metal sheet, held in place by current-carrying supports 13. Insulating gaskets separate these currentcarrying supports 13 from the outer wall 3 and an upper wall section 15, the assembly being clamped rigidly together by threaded rods 25 and nuts 26. The upper wall section 15 is provided with a channel member 16 at its upper end, containing water 17 into which a downwardly projecting rim 18 of cover 19 dips to form a gas-tight seal. The lid or cover 19' carried ya brine inlet pipe 23 and a chlorine outlet pipe 36 for the gas evolved during electrolysis. The body of the cell is filled with brine 27.

In use, the central cathode support is connected to the negative pole of the electrolyzing current supply by a suitable connecting lead (not shown) and the anode su-pports 13 are likewise connected to the' positive pole of the electrolyzing current supply. Brine is fed in through pipe 23 in the lid 19, and then flows downwards through the cell and is electrolyzed where it passes between anode 14 and mercury film 9, and finally flows out of the cell as spent brine through an outer pipe 28 situated `at a convenient position in outer wall 2. The mercury is fed in through pipe 4 and is taken out of the cell through pipe 11 as a weak alkali metal amalgam, which is then treated in an apparatus (not shown) for recovery of the alkali metal content, particularly as caustic alkali, and is then fed back to the cell for re-use. Chlorine evolved during electrolysis rises through the brine in the cell and is taken ett through the pipe 36. v

In FIGURE 2,` the apparatus shown is similar to that of FIGURE 1 except that the anode 14 is in this case an unperforated cylinder of which the upper end 14A extends above the upper lip S of the cathode support 2, and brine flow i's confined between ythe anode 14 and the mercury film 9. The other parts and the mode of operation are otherwise those described for FIGUREL I In FIGURE 3, the anode 14 and the cathode support 2 are conical in form and the anode 14 is carried on a current-supplying support 13 which passes out through the cover 29 of the cell through a gas-tight gland 39 and is provided with a threaded rod 31 and nuts 32 by which its position can be adjusted in a vertical direction.

In FIGURES 4 and 5, the cell comprises a body 40 provided with a clamped cover 41, brine inlets 42 and 43 (these are alternatives, but can both be used if desired), a chlorine exit pipe 44, and at its lower end an ex'itpipe and separator 45 through which amalgam and spent brine can be drawn off through pipes 46 and 47 respectively. The body 40 is filled with brine 48 and a hollow plateshaped cathode support 49 is held in place by attachment to a clamped base plate 5t). Two sheets of platinized titanium (sheet or mesh) 51 are disposed on opposite sides of the cathode support and anodically connected to a source of electrolyzing current by any covenient means (not shown). Mercury is fed through a pipe S2, through the hollow centre 53 of the cathode support 49, and spills out from the top of the plate and flows downwards over both sides of support 49 as a film 54 to collect at the bottom as a pool 55.

What I claim is:

1. Electrolytic cell for the manufacture of chlorine by electrolysis of brine having a vertically disposed cathode support in the form of a frustrum of a cone provided with means for flowing a mercury cathode lm thereon, and an adjacent, substantially parallel anode comprising titanium having a coating of a platinum metal on the surface thereof.

2. Electrolytic cell as claimed in claim 1 wherein the cathode support is in the form of a right frustrum of a cone.

3. Electrolytic cell as claimed in claim 1 having means for 4relative adjustment of the electrode surfaces in a vertical direction.

References Cited UNITED STATES PATENTS 2,599,363 6/ 1952 Bennett et al 204-219 2,762,765 9/1956 Kircher 204-219 2,876,192 3/1959 Wurbs 204-220 3,046,215 7/1962 Sullivan et al. 2041-219 FOREIGN PATENTS 233,388 8/1959 Australia. 490,911 8/1938 Great Britain.

JOHN H. MACK, Primary Examiner. E. ZAGARELLA, Assistant Examiner.

Claims (1)

1. ELECTROLYTIC CELL FOR THE MANUFACTURE OF CHLORINE BY ELECTROLYSIS OF BRINE HAVING A VERTICALLY DISPOSED CATHODE SUPPORT IN THE FORM OF A FRUSTRUM OF A CONE PROVIDED WITH MEANS FOR FLOWING A MERCURY CATHODE FILM THEREON, AND AN ADJACENT, SUBSTANTIALLY PARALLEL ANODE COMPRISING TITANIUM HAVING A COATING OF A PLATINUM METAL ON THE SURFACE THEREOF.

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