US1545383A - Apparatus for electrolyzing fused salts - Google Patents

Description

July 7, 1925.

E. A. AsHcRoFT APPARATUS FQR ELECTROLYZING FUSED SALTS Filed April 10, 1922 3 SheetgSheet l Jul-y 7, 1925. l1,545,383.

E. A, ASHCROFT APPARATUS FOR ELECTROLYZING FUSED SALTS Filed April 10, 1922 3 sheets-sheet 2 1,545,383 A E. A. .ASHCROFT APPARATUS FOR ELECTROLYZING FUsED sALTs Filed April 10, 1922 s s'heetsrsheet July 7, 1925.`

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l I I l I I l l ro vPatented July 7, 1925. y

UNITED STATES PATENT OFFICE.

Encan Alumina- Asncnor'r, or LONDON, ENGLAND.

:APPARATUS FOB ELIii-C1'.IRO'II'YZIIN125l FUSEI) SALTS.

Application led April 10, 1922. Serial No. 551,306.

therefrom,`and is moreespecially intended I foruse in the electrolysis of metallic chlorides. such as chloride ofzinc, or chloride of lead, andthe recoveryof the metal and chlorine.

My invention is hereinafter described as I applied to the-electrolysis of zinc chloride,

y supply conductors.

but I may use it for 'thedecomposition of any other suitable salt and also for the production of alloys from `mixtures of chlorides or other suitable salts.

Hitherto inthe eletrolysis of fused salts separate'couples have been employed, each couple consisting of van anode of carbon, or

graphite, and a fused-metal cathode ar. ranged within a container for the fused materials.

. The electrolytic apparatus according to my invention'consists of a multiple couple` electrolyzer comprising a series of closelyspaced electrodes all to be immersed in the same body of molten electrolyte contained in a refractory and preferably heat-insulated container, only the first and last of the electrodes being connected with the electric The inner wall of the container surrounds, or embraces, the edges ot' the series of electrodes, ,thus preventing excessive leakage of lcurrent ast the edges, and passages are provided 'or leading olf separatelythe metallic and gaseous products of the electrolysis. The electrodes may 'if desired, be all of' thesame composition, for example 'of compressed carbon, or

graphite, and any convenient number of' couples may be employed, the opposedsurfno . 'faces of any two adjacent electrodes and the intervening space filled with electrolyte constituting what I term a couple.

Apparatus embodying lmy invention is showin in the accompanying drawings in which' v Y Fia 1 is a vertical section through an electrolyzer;

-Fig. 2 is a removed;

plan thereof with the cover Figs. 3 and 4 are views corresponding respectively to Figs. 1 and 2, "but illustrating 'a modified construction; I

F lgs. 5 and 6 are al`so"v1ews correspond-V ing respectively to Fi 1 and 2, but illustrating a further mo ilication of construc- The accompanying drawings. and description relative thereto afford examples ofthe apparatus constituting my,` invention.

Figure 1 represents in vertical section and Figure 2 in plan (with the cover removed) an electrolyzer having eleven lates or electrodes constituting between :t em tenl electric couples o f rectangular form arranged in a container also of'general rectangular form. In Figure 2 each electrode is shown as consisting,- for convenience, ofl three pieces.

'Ihe container A (which is surrounded by heat insulating material such as kieselguhr) is' made of refractory non-conducting Inaterial, or consists of a metallic chamber with -afreiractory non-conducting lining, and the te'nelectric couples are formed by the electrodes B1 to ,B13 arran ed .in an inclined position one above anot er, there being a space a above the electrolyte in' which space the chlorine collects and passes into an escape-pipe D.- -A reservoir a2, at the base of the apparatus, receives the molten zinc produced, which can be removed periodically at a tap-hole as.

The positive conductor from any suitable source of continuous' electric current is passed through a tightly packed o ening in the cover A2, and is connected wit the top electrode in`an convenient manner, preferably by rods of graphite, or other suitable material, screwed into the plates constituting the electrode. A graphite rod E2 enters the reservoir ai of molten zinc and so under operating conditions makes electrical connection with the lowest electrode, the said rod E2 passing up, through a tubular Cavity, e2, in the Wall of the ,container A,

to the upper part of the apparatus for connection to the negative pole ofthe electric supply. The electrodes are lates of ite, or other suitable materia ,incline preferably at a considerable angle as shown and separated by distance pieces, or rests, b of fused silica, vitreosil, obsidianite, or` other aplip. l

hard., hea-t-reSiStant-and. electrically-insulto -ing material, the supports b1 for the lowest providing an insulating shield to tlie edges of theelectrodes; but holes b2 nearthe lower ends of the electrodes allow the zinc to descend to the reservior a?, and holes b3 vnear the upper ends allowy the chlorine gas to escape to the space al, circulation of the electrolyte C also taking. place.

A closable opening at in the cover of the apparatus serves for the introduction of fused zinc chloride, preferably at a temperature of about 350 to 400 C. as this prevents fuming of the fused salt.

The apparatus vis provided with means for feeding in chloride to replace that decomposed by the current and in this manner the apparatus can be worked continuously for a long time. The fusion of the electrolyte may be maintained by means of the electric current, and external heat may be applied to the container, as hereinafter explained. The fusion may also be maintained wholly `or in part by providing the apparatus with means forapplying a supplementary alternating current to the first and last electrodes of the electrolyzer, such current being more economically produced than the continuous currentnecessary for electrolysrs.

The electrolysis will vset free zinc (in the instance given) on the upper surfaces of the electrodes and a corresponding `weight of. chlorine on the under surfaces. The. zinc will flow downwards into the reservoir a2, and the chlorine will rise to the upper .part a, and they do not comeagain into contact after being separated by the current. Satisfactory circulation of the electrolyte throughout lthe apparatus is caused by the upward flow of the gas and the downward flow ofthe metal.

The use of a multiple-couple electrolyzer constructed in accordance with my inventionv results in economy of electrical energy the use of a more convenient voltage, and variou-s advantages as regards cost of construction, working and upkeep of the apparatus. In order to understand these advantages the principles of the electrolysis `of fused metallic salts generally and of zinc chloride in particular may be considered.

Theoretically the chemical voltage required for the kdecomposition of zinc chloride ina state of fusion is approximately-1.6 volts and the Faradaic yield, per ampere hour, 1,218 grams; therefore'the minimum energy required to produce one kilogram of zinc is 1315 watt-hours, exclusive of that needed to keep the'electrolyte in the molten condition. For technical reasons it. is prefcrable to keep the electrolyte fused by internal electrical heating, due to` extra terminal voltage xor to a supplementary alternating-` current.. It followsthat efficientheat insulation is a prime factor in economy. It is necessary in all single-couple apparatus known tol meto employ a high current densit andthe loss of heat thro-ugh the electro es isconsiderable; consequently, in the best formof such single-couple apparatus, the terminal vqltage per couple is believed to be approximately three times the necessary chemical voltage, and with a cur; rent efliciency of'9() per cent. The energy eii'iciency cannot be raised much above 30 per cent. The lower the current density employed at the electrodes, with a view 'to securing low terminal voltage, the more accentuated-are the diiicultie's of practical heat conservation such diiculties being due to the increased size and inconvenient form of the apparatus designed for `such a purpose. It is usually found that the economical lower limit of current density is about four, to six, amperes persquare inchof electrode surface, and greater current densities have often been employed.

lith my multiple-couple electrolyzer current densities of from two amperes to one ampere and even les-s, per square inch of electrode surface can be employed. The space between the electrodes may, be reduced to halfan inch, o-r evenless, anda lo-w terminal voltage per couple can thus be obtained. The passage of a small leak current through the holes and around the supports, or separators, (which are loosely placed between the ends uof the electrodesA and retained in positionby their grooved and rabbeted formation) results in a slightlylower current efficiency than is obtainable with a single couple, but the energy so passed fulfills the useful vofice of maintaining \,the electrolyte in fusion. VVlth such an apparatus, using only two volts per couple (that is twenty volts overv the whole apparatus having ten couples), results have been obtained equivalent to a total energy eiiiciency of 64 per cent. of the theoretical, which is Inore than double the efficiency understood to be realizable by employing the hitherto known lprocess and forms of apparatus.

But besides' a saving Iof electrical energy, constructional advantages lare obtained. Not only is the apparatus compact and simple to build and tomaintain, but the 1inportant advantage of low amperage, with a corresponding reduction in the number and size of the electrical connections, resnlts. Thus, in order to absorb the energy from a given source, it is delivered to the electrolyzers at a relatively lo-w aniperage and high voltage (instead of vice versa in the case of anI installation of single-couple clectrolyzers)l and this permits a reduction both in the number of apparatus employed i. tained in a highly concentrated condition.

A modified form of electrolyzer in accordance with my invention is shown in sectional.

elevation` in Figure 3 and in plan, (with t-he cover removed) 4in Figure 4. The apparatus here illustrated has a circular container A, and colloidal or funnel-shaped, electrodes,

inclined towards the centre, contact being madewith the reservoirof zinc in the base of the apparatus by means of a central graphite rod E2, passing through a silica tube e3 with openings in it at e4. The parts in these igure's Which correspond with those shewn in Figures 1- and 2 are marked with the same reference letters.

Another frm of my electrolyzer is shown in sectional elevation and plan (with the tively. This electrolyzer contains a number of vertical saddle-shaped electrodes, B1 to B", placed over dividing partitions of refractory material. In this case the zinc gathers in the separate compartments a2 in the lowerfpart of the .container and can be drawn off from separate outlets a3, or from a common channel. The chlorine given off passes into the common space ja above the top of the electrolyte at C and to the pipe D and thence to the required place. The electrodes B and B10 at each end of the container are respectively connected by the rods E and E2 of carbon, or other suitable matetlie Walls of the cbntainer being constructed -of a thickness suitable for this purpose.

Having noiv particularly described and ascertained the nature of my said invention, and in what manner the same'is to be performed, I declare that what I claim is.-

1. A metallurgical electrolyticI apparatus comprising a container for a fused melt, 'a group -of closely spaced electrodes immersed in and electrically connected in series by the melt undcraoperating conditions, and

` means for establishing current How succes- .cover removed) in Figures 5 and 6 respec- 'establishing sively through the several electrodes and interevening portions of themelt to4 constitute a lgroup of electrolytic couplesy arranged in eletrical series below the surface of the me t.

2. A metallurgical electrolytic apparatus comprising a container for a fused melt, a group of. closely spaced electrodes immersed in and electrically connected in series by the melt under operating conditions, means for current flow successively through the several electrodes and intervening portions of the inelt to constitute a group `of electrolytic couples arranged in electrical rial, to the respective poles of' the source of* electricity.,

I may use graphite plates, arranged simi'- larly side by side and supported in grooves, or` the like, in the Walls, or lining of the container.

It is to be understood that I do not limiti In' order to ensure heat insulation I may surround the container on all-sides Witlr va bed of non-conducting material, such' as kieselguhr,"\and this will usually be found I may employ any convenient.

sufficient; but I may 'alternately apply eX-' ternal heat, derived from anycheaper source than electric energy; for instance, by means of a jacket in which superheated steam, or hotair, oil, or other fluid is circulated at a temperaturey sufficientto maintain the exterior of the container at about 20Go-300 C.,

series lbelo-W-tlie surface of the melt, and means for substantiallycondning the flow of current to the couples in the electrolytic zene of the apparatus. -f

8. A metallurgical electrolytic apparatus comprising a container for a fused melt, a groupof closely spaced electrodes immersed in and electrically connected in series by the lUI melt under operating conditions, and means for establishing 'current flow successively through the-several electrodes and intervening portions of the melt to constitute a l group of electrolytic couples arranged in Instead of these saddle-shaped electrodes,

electrical series below the surface yof the melt, together With meansf for leading the products of electrolytic decomposition in4 -through the several electrodes and intervening portions of the melt to constitute a group ,of electrolytic couples arranged in electrical series below*A the surface of the melt, together with means for leading the products of electrolytic decomposition in different directions through the melt to effeet a circulation of the latter. f

5. A lmetallurgical electro-lytic` apparatus comprisin la container for a fused melt, a

group of c osely spaced electrodes immersed in and electrically connected in series by `the melt under operating conditions', and4 means for establishing 'curr-ent flow successively through the several electrodes and intervening portions of the meltto constitute a group of electrolytic couples arranged in l electrical series below the surface of the melt, together' with means for leading the heavier products of electrolytic decomposition downward in one portion of the zone of electrolysis, and the lighter products of electrolytic decomposition upward in another portion of said Zone.

- 6. A metallurgical electrolytic apparatus comp-rising a container for a' fused melt, ya

`grouplof closely spacedelectrodes immersedrin and electrically connected in' series by 7. In a metallurgical electrolytic appara? tus having a container for a fused melt, an electrolytic couple 'comprising a pair of spaced electrodes adapted to receive the fused melt therebetweem'the active surfaces of the electrodes being arranged at an angle to the horizontal, a passage at the upper portion of the upper electrode for the escape Kof gaseous products of electrolytic decomposition of the melt and a passage at the lower portion of the lower electrode for theV escape of heavy products of electrolytic decomposition.

8. In a metallurgical electrolytic apparatus, a container for a fused melt, a pile of spaced electrodes immersed in the melt under operating conditions, and having their active surfaces inclined to the hori zontal, the intermediate electrodes of the pile .having at their upper portions passages for the upward escape through the pile of gaseous products ofielectrolytic decomposition, and passages at their lower portions for the downward flow through the pile' of heavy metal ,products of electrolytic decomposition.

9. .A metallurgical electrolytic apparatus comprising a container fora fused melt,

a group of closely spaced electrodes immersed in and electrically connected in series by the melt un'der operating condi-- tions, mea-ns for substantially conning the current to flow in series through the electrolytic couples thus established, a current supply connection to the electrode at one end v -of the electrodegroup, and a second current supply connected to the electrode at the other end of the group.

` 10. A metallurgical electrolytic apparatus comprising a'. container for a fused melt, a

group of closely spaced electrodes immersed in and electrically connected in'series by the melt under operating conditions, means for substantially confining the current to llow in. series through the electrolytic couples thus established, a current, 'supply connection to the-electrode at one end of the electrode group, and a second current supply connection to the electrode at the other end of the group, said latter connection being established under opera-ting. conditions through a fused co-nductor.

11. A metallurgical electrolytic apparatus comprising a container for a fused melt, a group of closely spaced electrodes iinmersed in and electrically connected in series by the melt under operating conditions, means for substantially confining the current to flow in series through the electrolytic couples thus established, a well for the reception of a fused metal product of electrolytic decomposition of the melt, a current supply connection to the electrode at one end of the electrode group, and a second current supply connection to the fused metal in said Well.

12. 4A metallurgical electrolytic apparatus comprising a closed top container for a fused melt, a pile of spaced electrodes immersed in the melt under .operating conditions current supply conductors passing through the top of the container, one of said conductors being connected to the top e1ectrode of the pile, and die second conductor being in electrical connection with the bottom electrode of the pile, together with insulating means sepa-rating the second con# ductor from the upper electrodes of the pile and from the fused melt above the bottom electrode and causing substantially the entire'c'urrent supply to pass in series from the 'top electrode to the adjacent electrode through the intervening stratum of the melt, anld so on downward through the electrode 13. Multiple-couple electrolyzer for fused salts, comprising a refractory container' for the fused electrolyte and the gaseous and metallic products, provided with feed and discharge openings andc a series of closely spaced electrodes so positioned within the container as to become immersed in the electrolyte while the electrolyzer is in operai ion, the container 'embracing the outer edges ol the electrodes and only the first and lust of the electrodes being connected with the external sup ly conductors.

14. Multip e-couple electrolyzer'for fused salts, comprising a heat-insulated refractory container for the fused electrolyte and the gaseous and metallic products, provided with feed and discharge openings and a series of closely-spaced electrodes so positioned within the container as to become ilumersed in the electrolyte while the electrolyzer is in operation, the container embracing the outer edges ofthe electrodes and only the first and last of the electrodes being connected with 4the external supply conduetors.

15. Multiple-couple electrolyzer for fused salts, comprising a refractory lcontainer for the fused electrolyte and the gaseous and metallic products provided with a jacket for' the circulation of heating fluid, feed and discharge openings and a series of closelyspaced electrodes so positioned within the container as to beeorneimmersed in the electrolyte while the electrolyzer is in operation, the container embracing the outer edges of the electrodes and only the first and last of the electrodes being connected with'the external supply conductors.

16. Multiple-couple electrolyzers for fused salts having a series of closely-spaced inclined electrodes provided with holes in their upper and lower parts for passage of the electrolyte and the products of the electrolysis, only the first and last of the electrodes eing connected with the external supply conductors.

17. Multiple-couple electrolyzer for fused salts having a' series of closely-spaced in clined carbon electrodes provided with holes in their upper and jlower parts for passage of the electrolyte and the products of the eleetrol sis, only the first and last of the electro es being connected with the external supplyy conductors.

provided with holes in their upper and v lower parts for the passage of the elec# trolyte and the products of the electrolysis, only the first and last of the electrodes1 being connected with the external supply eonduetors. i

20. Multiple-couple electrolyzer for fused i salts having a series of closely-spaced inclined carbon electrodes separated by 'distance-pieces of insulating, heat-resistant materi'al and provided with holes in theirupper and lo'wer parts for passage of the electrolyte and the products of the electrolysis, only the first and last of the electrodes being connected with the external supply conductors.

In testimony whereof I have signed my naine to this specification in the presence of two subscribing witnesses.

EDGAR ARTHUR ASHCROFT.

Witnesses:

G. F. TYsoN, EDWD. GEO. Davms.

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