US3234115A - Process for the electrolytic precipitation of sodium - Google Patents

Description

Feb.8,1966 K. ZIEGLER Em. 3,234,115

PROCESS FOR THE ELECTROLYTIC PRECIPITATION OF SODIUM Filed July :51, 196s INVENTORS/ BMWLWM United States Patent PROCESS FOR THE ELECTROLYTIC PRECHPI- TATION F SODIUM Karl Ziegler and Herbert Lehmkuhl, Mulheim (Ruhr),

and Wolfram Grimme, Moers-Utfort, Germany, assignors to Karl Ziegler, Mulheim (Ruhr), Germany Filed July 31, 1963, Ser. No. 299,689 Claims. (Cl. 204--68) This application is a continuation of application Serial No. 27,219, filed May 5, 1960, now abandoned.

This invention relates to a process for the electrolytic precipitation of sodium.

The production of metallic sodium by cathodic deposition of the metal in an electrolysis ot sodium-containing compounds is known. A distinction must be made between two different types of sodium production. In one embodiment, fusion electrolyses 'are effected with sodium hydroxide or sodium chloride, the melting point of which is lowered Yby the addition of calcium chloride. Naturally, this mode of operation and especially the sodium chloride electrolysis required relatively high electrolysis temperatures.

In the second type of elec-trolytic sodium production, metallic sodium is irst dissolved in a mercury cathode to form the amalgam by electrolysis of a warm sodium chloride solution. This amalgam must be freed from its sodium content in a secondary electrolysis in which it constitutes the anode and wherein the metallic sodium is deposited cathodically. This secondary electrolysis cannot be effected in the presence of water, the electrolyte being rather a molten bath of sodium hydroxide, sodium iodide and sodium bromide. The electrolysis temperature -is about 250 C. It cannot be avoided at this high temperature that murcury enters the metallic sodium, the reason being probably the fact that the vapor pressure of mercury is very high at the high electrolysis temperature required. The molten electrolyte saturates with this mercury vapor and the sodium at the cathode will again absorb this mercury portions. The deposited sodium from the secondary electrolysis must be subsequently freed from mercury not only because of the usability of 'the sodium lbut also for economical reasons since otherwise the mercury losses would be prohibitive. This purilication is accomplished by an additional treatment with some metallic calcium which combines with the mercury to form a solid calcium amalgam from which the molten mercury-free sodium can be decanted. The mercury may then be recovered from the calcium amalgam, e.g. by decomposition with an acid. In total, these operational measures are complicated and many process steps are necessary.

It is an object of this invention to provide a novel process for the electrolytic production of sodium, which process involves simplifications and facilitations in many respects over the prior art and which is particularly suited for the cathodic precipitation of pure sodium which contains only traces of foreign matter.

This object is accomplished in accordance with the invention by a process for the electrolytic precipitation of sodium which comprises subjecting to electrolysis molten baths of complex compounds of the general `formula MeAlRR' wherein Me is sodium or a mixture of sodium and potassium, R is an alkyl radical and R is hydrogen, an alkyl, alkoxy, cycloalk-oxy and/ or an aroxy radical which, if desired, may be substituted, while preventing any free metal alkyls which may be formed anodically, especially aluminum trialkyls, from becoming commingled with the sodium deposited at the cathode. Suitable electrolytes for carrying out the process of the invention are especially those complex compounds of CII 3,234,l l5 Patented Feb. 8, 1966 HCC the general formula given above, wherein R is a straight chain alkyl radical having preferably from 2 to 6 and especially 2 carbon atoms and R is hydrogen, a straight chain alkyl radical having preferably 2 to 6 carbon atoms and especially 2 carbon atoms or an organic radical OR wherein R is an alkyl, cycloalkyl, phenyl or alkyl-substituted phenyl radical. Electrolytes wherein R is hydrogen are preferably used only in specific embodiments of the invention which are dealt with hereinafter.

It has been -found that it is one of the essential conditions for the deposition of pure sodium at the cathode that aluminum complex compounds are used as electrolytes, which are suliciently stable in the molten bath at the temperature of the electrolysis, i.e. will not undergo decomposition into their individual components (free aluminum alkyl compound and complex-former) to an extent that the deposit of pure sodium is interfered with, and/or are not reactive with the sodium metal at the electrolysis temperatures used. This basic requirement of the process of the invention is met by the compounds of the general formula MeAlR3R mentioned above.

In one of the most convenient embodiments of the process of the invention, the electrolysis is effected on electrodes -Which do not participate in the chemical reactions involved in the electrolysis, i.e. both the cathode and the anode consist of inert metals such as, for example, copper, silver, gold, platinum, palladium, iron, cobalt, nickel, manganese, osmium, iridium or other inert metals. Alloys such as brass may also be used. With these electrodes, sodium is deposited on the cathode while the gaseous decomposition products of the ethyl radical are evolved at .the anode. When using the complex compound MeAlR4, i.e. an `aluminum tetraalkyl complex compound as the electrolyte, an aluminum trialkyl is simultaneously formed at the anode per metal equivalent deposited. If this evolved aluminum trialkyl would not ybe prevented Ifrom becoming commingled with Ithe cathodically deposited sodium, the latter would diffuse through the electrolyte towards the cathode where it would disturb after a short period of time the deposit of sodium with simultaneous deposition of aluminum.

Accordingly, in accordance with the invention, the free metal alkyls formed at the anode are prevented from being mixed with the sodium deposited on the cathode. To this end, two different possibilities exist fundamentally, i.e. the use of mechanical or physical means which exclude such undesirable commingling and an intensional control of the chemical processes in the electrolyte which likewise prevent an undesirable back reaction involving the deposited sodium. 1

The mechanical or physical means include especially the following:

(a) inserting a diaphraghm between the anode and cathode or (b) Etfecting the electrolysis -in vacuo, the vacuum having to be such that the anodically formed metal alkyls ydistil out directly from the electrolyte liquid prior to being able of migrating through the electrolyte to the cathode. In this embodiment, it is not advantageous to use ine-rt anodes since this would involve the necessity of constantly pumping off an excessively large -amoun-t of gas. This embodiment is suited for the use of anodes on which the alkyl radical is lcombined to form metal alkyl compounds rather than to 'be decomposed.

When operating with a diaphragm inserted between the cathode and the anode, it may `be desirable to maintain a liquid liow from the cathode space into the anode space, which iow is preferably slow. This is, for example, accomplished in a convenient manner by maintaining the liquid level in the cathode space somewhat higher than in the anode space so that this desirable concell. For example,y satisfactory operation can be achieved at pressures of Ibelowrl mm. Hg. As has been found, the removal of the formed free metal alkyl compound "by distillation must `be effected so rapidly that specic 'maximum concentrations ofthese 'alkyl compounds in the electrolyte are notl exceeded. In casefof aluminum ltriethyL'this maximum concentration is about 3% and preferably about 1%. Apparatus suited for carrying out the process of the invent-ion is disclosed ,in our U.

Patent Nos. 2,985,568'and 3,069,334 which describe both the useofthe diaphragms-me'ntioned above and' operation in vacuo.v Y A The alternative of preventing the undesirable-back reaction by controlling the chemicalprocesses withinfthe electrolyte is also realizable by dile'rentme'thods. for example, aluminum triethyl is evolved at the anode during the electrolysis, the same may in lone embodiment of the :proce-ss of the' invention ibe prevented from react.-v

ing `with the sodium by adding .alkoxy or `aroxy complex compounds `of the general formula MeAlRBORf' wherein Me, R, and R have thev meaning mentioned above. VIn doing so, the free aluminum trialkyl isconverted into the alkali metal aluminum tetraalkyl compound7 i.e. into an i electrolyte which is `among those electrolytes which are suitable for the process of the invention, while free alu-v minum compounds of the general formula AlRgOR" are simultaneously formed. It appeared surprisingly that an undesirable re-conversion does not Voccur in this embodiment of the process. While free aluminum trialkyl undergoes decomposition with sodium at temperatures of as low as about 100 C., such decomposition does not occur between an alkoxy or aroxy valuminum dialkyl and sodium metal in the temperature range which isA suitable for carrying out the process of the invention, i.e. at temperature up to about l50-160 C. Arr-undesirable.conversion will only occur if the temperature exceeds this limit. Addition of the complex compound MeAlRaOR may be efected batchwise, i.e. in adequate amount'at the beginning of the electrolysis, or preferably continuously during vthe electrolysis atthe rate required.

' Thus, when constantly converting any evolved portions of'free aluminum trialkyl into the corresponding alkoxy or aroxy aluminum dialkyl compounds by the preferred continuous addition of the MeAllRgOR compounds, pure sodium may Ibe deposited cathodically up to about 150 C.even without the use of mechanical means.`

sible -for carrying `out this embodiment vof the invention by adding at least the necessaryamounts'of MeAlRgOR to Vuse this seceond complex compound even as the sole electrolyte. Howevendue to the relatively poor electric conductivity of the alkoxy complex compounds, the use of the tetraalkyl complexes as the main electrolyte is preferred.

It anodic evolution of still other metal alkyl compounds occur which undergo no reaction with the aluminum alkoxy complex compound, ythe use of mechanical means for the separation of the anodi-c reaction product from the cathodically deposited metal is indispensable.

Of the compounds of the general formula MeAlRSR to'be used as the electrolyte in 'accordance with -the 'in- Besides theuse of MeAlR4 as the main electrolyte, it is also posvention those compounds wherein Me is potassium have Ia considerably better conductivity than the correspond It also appeared that if a mix#y ture of potassium and sodium tetraalkyl complex corn-l pounds is subjected to electrolysis, pure sodium is depos-A ing sodium compounds.

ited as long as the potassium portion does not exceed about ofthe alkali metal. For this reason, Vit is, 'preferred to use mixtures of -sodium andvpotassiumr complexcompounds of the general formula MeAlRBR as the electrolytes. During the; electrolysis, this electrolyte becomes poor inthe -sodium compound which must then be supplied Vbatchwise or continuously at an appropriatek rate such that the potassium content will not exceed about 80%.

For continuous operation, the amount fof sodium aluminum complex compound decomposed during the elec.-

trolysis must Ebe renewed lbatch'wisefor continuouslyeven when working with nopotassium compound. A`When operating vwith'rnechanical vrneanstor removing theanodically evolved free aluminum ltrialkyl, 4the same may 'ad vantageously `be reused .'for the `production'ofthe soduim-aluminum. tetraalkyl,` compound. `Tothis end,'it is vtransferred together with fresh "sodium in'to apressure reactor and reconverted :into `the`1electrolyte compound 'by treatmentfwith hydrogen and Subsequentlvwith the correspondingoletin A suitableprocess, forthis conersion is, forexample, that disclosed in Ger-man Patent 'No 917,006. In this manner, cyclic processes may, for

example, ybe carried out for the :refining of-"s-odium with the latterbeing introduced into the process cycle in the regeneration of the e'lectrolyte,fandV the puriefd'metal being cathodically withdrawn.

Cyclic processes of thisftype may also be carried out in cases Wheretheformed free aluminum `trialkyl compounds are converted vwithin the electrolyte into the free alkoxy or aroxyaluminum dialkyl compounds by the addition of MeAlR3OR-. For this'purpose, the compounds of vthe formula AlRzORare` then reconverted outside of the electrolytic cell into the compounds MeAlR3OR, and these are then again returned' into the electrolyte as electrolyte or for reaction with the aluminum trialkyl cornpounds. The best possibility'ofv yregenerating the compounds of the general formulay MeAlRaOR is toreact the compounds of the formula RZAlOR'f, together with Y alkali metal hydride, with the lappropriate olefins, eg.`

ethylene. The treatment with the oleiins may be effected atftemperatures between v and 220 C.' and preferably between 'and 200 C. and pressuresup to 100 atmospheres and preferablybetween l and 20vatmospheres. v

The. deposition of sodium of .highest purity for any period of electrolysis desired :isjal'so possible by a different and particularly preferred embodiment of the process. In this preferred embodiment vof the, processof the invention,` the. molten electrolyte ,body of compoundsof Vthe general formula MeAlRaR isisubjected to electrolysis at a cathodeV of an inert metal anda sodium-.containing anode. It `was found vverysurprisingly that this permitsV in most convenv vplex compound,y constant electrolyte composition is al-Y ways maintained in this manner; lThe need for the use of any mechanical means for preventingundesirable backk decompositionsis thus completely eliminated just as the.

batchwise or continuous renewal of consumed electrolyte. Various sodium-containing materials maybe used as 'the anode material. Anexample otra suitable material is *spagna molten raw sodium, This involves the simplest form of electrolytic sodium refining in carrying out the process of the invention. Other anode materials are also usable.

Particularly preferred is the use of sodium amalgam as the anode material. This sodium amalgam is, for example obtained in large amounts in the electrolysis of aqueous sodium chloride solutions, which electrolysis is currently widely practised. As was already mentioned above, the recovery of pure sodium from these solutions has been relatively difficult and complicated up to the present. The process of the invention now provides a new route to the direct production of sodium of highest purity from this sodium amalgam, especially by the use of the novel electrolytes. Due to the possibility of effecting the electrolysis at considerably lower temperature than heretofore, but under at least equally favorable conditions with respect to current utilization, it is accomplished in accordance with the invention in a single operational step to obtain sodium of highest purity which needs not be subjected to further complicated purifying operations. The degree of purity of the sodium `deposited at the cathode is further improved by the possibility of reducing the electrolysis temperature to a relatively low level. The sodium amalgam preferably used in this embodiment of the process of the invention is an amalgam which is obtained in the electrolytic production of alkyls of metals of group II and main groups III to V of the Periodic Table by electrolysis of aluminum-organic compounds. In such a process, electrolytes containing compounds of the general formula Me[AlR3R] are subjected to electrolysis on anodes of the metal the alkyls of which are to be produced and on a mercury cathode. In the general formula given above, R is an alkyl radical, R is an alkyl, alkoxy or aroxy radical, which aroxy radical may be substituted, or fluorine and Me is sodium, potassium or a mixture of sodium and potassium. The electrolyte may in addition contain compounds of the general formula AlRzR wherein R is an alkyl radical andR' is an alkyl, alkoxy, or aroxy radical, it being possible in the case of R=alkyl that the aluminum trialkyl compounds then present are added as etherates 0r A trialkyl aminates. It may further be advantageous if all radicals R are identical and, in the case of R=alkyl, the radicals R and R likewise are the same alkyl radicals. The preferred starting electrolytes are compounds of the general formula MeAlR4, MeAlR3OR" (wherein R" is an alkyl radical having preferably from 2 to about 20 carbon atoms and especially from 2 to 8 carbon atoms, a cycloalkyl radical or, if desired, a substituted phenyl radical) NaF.AlR3, NaF.2 AlR3 and/or mixtures thereof. It 1s then possible, for example, to produce alkyls of the following metals: Beryllium, magnesium, mercury, aluminum, gallium, indium, lead, arsensic, antimony or bismuth.

Sodium amalgam is cathodically formed in an electrolysis of this type, it being preferred that the sodium content in the amalgam does not exceed about 1.5% by weight since this permits simple withdrawal of the sodium -amalgam which is then still liquid. To permit the re-use of the mercury for the production of metal alkyls, it must be freed at least partially from its sodium content, which can be accomplished by the process of the invention.

It must be considered as extremely surprising that the performance of the process of the invent-ion with formation of sodium ethyl from sodium amalgam is possible -at all. As is known, mercury is among the metals which, when used as the anode metal in the electrolysis of aluminum-organic complex compounds, form volatile metal alkyls. Since the reactivity yof sodium in the amalgam is considerably reduced as compared with that of pure S0- dium, it could not be predicted that it is actually possible to transfer the sodium out of the amalgam into sodium ethyl without the simultaneous formation of mercury alkyls. This is lthe more true when considering the fact that lithium amalgam and mercury alkyls can be produced by shaking lithium alkyls with mercury:

6 This is an equilibrium reaction and it is clear that, if such a conversion would play a part also in case of so= dium, the smooth separation of sodium from the amalgam ywould not be possible.

The .attack of the ethyl radical takes place at the surface of the amalgam layer, where the sodium is consumed so that the surface becomes more and .more enriched with mercury.

When operating with electrolytes MeAlRgR wherein R is alkyl, alkoxy, or aroxy and using suti'iciently high current densities that the formation of sodium alkyl proceeds at .a rate higher than that of the diffusion of sodium metal from the interior to the amalgam surface, an undesirable formati-on of mercury alkyls may occur. It is preferred, therefore, to set an upper limit to the current densities used with the range up to `about a./dm.2 being particularly preferred. Particularly suit-able is the range from :about 10 to about 50 a./dm.2. In addition, this deficiency may be remedied by agitation of the sodium amalgam.

If, furthermore, the amalgam becomes progressively poorer in sodium a-s the electrolysis proceeds, the risk of the undesirable forma-tion of mercury alkyl becomes greater. This will with certainty occur after the last residue lof sodium has been removed from the mercury.

It is, therefore, preferred in :accordance with the invention to leave always a suiiicient residual content of sodium in the amalgam rather than effecting the electrolysis until the sodium is completely removed. This residual sodium content may, however, range below 1% and is, for example about 0.2% to 0.5% of sodium. This does not restrict the applicability of the process of the invention since the mercury :anyhow serves in a cyclic process .as the receiving agent for the primarily precipitated sodium .and any residual sodium content is, of course, -unimportant in such .a cyclic process.

When using sodium-containing anodes, the electrolysis is carried out particularly advantageously with the electrolytes of the gener-al formula MeAlRgR' wherein R has the meaning referred to above and R is hydrogen. In electrolyzing these compounds, the hydrogen radical rather than an ethyl radical is bonded to a sodium which goes into solution. However, as long as this reaction of hydrogen is preferred to the corresponding reaction of the ethyl radical, the risk of an undesirable formation of mercury compounds is excluded since sodium hydride and consequently the corresponding electrolyte complex compound (by reaction with the aluminum-containing compound simultaneously formed anodically from the decomposition of the electrolyte) but no mercury hydride can `be formed. The hydride-containing electrolytes may also be electrolyzed advantageously on -inert anodes. As long as the overvoltage of hydrogen on these anodes is not sufficient that the discharge of the ethyl radicals occurs easier, hydrogen is then anodically evolved in place of the gaseous decomposition products of the ethyl radical. This hydrogen may then be used in a simple manner to assist in the regeneration of vthe electrolyte. In the case lof using anode met-als of groups Il to V of the Periodic Table which are converted into the corresponding alkyl compounds during the electrolysis, the use -of the hydridccontaining complexes is less suited since undesirable back reactions may occur within the electrolyte.

In a particularly simple .and preferred `embodiment of this modification of the process, the electrolysis is carried out as a three layer processs wherein the heavy amalgam layer is at the bottom followed -by the molten electrolyte while any inert metal cathode, e.g. in the form of a net, is arranged at the surface of the electrolyte. The sodium is then precipitated round the cathode. It appear-ed, however, that the specific gravity of Isodium is higher than that of the molten electrolyte so that if the electrolysis is effected at temperatures at which the sodium is present in molten state, this molten metal would drop downward through the electrolyte and onto the .as compared with a single cell.

amalgam anode there-by aggravating the process. Accordl` to be 0.05 to 0.1, i.e. the sodium has only about 1&0 to v 1/10 of its actual lweight in the electrolyte. "liurthermore,v the surface tension of molten sodium in the molten elec.-

-trolyte isVV very high. Thus, very important surf-ace or capillary forces are existing at the `interfaces between sodium and the electrolyte. The c-onsequence hereof is that already a very wide-m-eshednet of a Suitable insulating material which, for example, is .arranged vhorizontally in the electroylte at .a distance of a few millimeters above v the ymercury surfa-ce will suffice completely to -keep a sodium `layer having a thickness of even several centimeters iloating and to prevent it from` sinking down.

or, still better, from a glass liberv fabric. the process may be operated with voltages of about 1 v.

The. performance of the electrolysis is, however, not

restricted to the mode of operation described above.` Use may als-o vbe lmade of differentV electroyticv cells. Thus,

the electrolyses of truly inorganic electrolytes arel ef-r feet-ed with rotating vertical disc electrodes which are immersed with their lower parts in the amalgam, arewetted with the amalgam and which face metallic cathodes with their upper halves. su-chthat the deposited sodium glides .along the cathode andl sinks in downward direction, it can thereby `be dis'- -charged laterally from the bottom of the electrolytic cell.

On principle, the process of lthe invention is operated at temperatures at which thesodiurn is deposited` as a liquid on the cathode. Since the melting point of sodium is about 97 C., the preferred temperatures range about 100 C. and especially between about 100 and about 150 C. The lower `temperatures are used for the production of particularly pure sodium so that, when working at a temperature slightly exceeding 100 C., a sodium product which contains only a few parts per mille of mercury can be obtained in a once-through electrolysis.`

However, included within the `scope of the `invention is also the use oftemperatures below 100 C. at which, for example, the mercury content of the deposited sodium can be reduced still further. Since, however, temperatures in excess of 100 C. facilitate the performanceyof the process and favor the current yield, thev use of the temperature range mentioned above is particularly advantageous.

Where a particularly high purity of the cathodically mediate layer of sodium acts as the cathodeandthe top E.

face as the anode. In this manner, the raw sodium derived from the sodium amalgam is first deposited in the in-v termediate layer and, linally, the pure sodium isydeposited at the `upper cathodein highest purity by repeatedelectricalreiining of the middle layer of raw' sodium. Since the distances between the cathode and anodeneedf not: 70 be greater than a few millimeters, the current require'-l ment of such a double cell is practically hardly increased Relatively low voltages, e.g. of about 1.5 to about 5 v., may be used inthe process.

When. using ,inert Vvelectrodes. inthe process .ot the; `in

The surface tension preventsrthe,sodiumafrom passingthrough the net. The. net itself may consist of cellulose filaments ln this case,

If the cathodes .are given a shape deposited sodium is desired, this can be achieved by vention, i.e. if Asodium ethyl orI other-metal alkyls arenot formed at the anode, the process may be carried out in any electrolytic ,cell providedtliat care is taken that-a connection with 'metallic conduction is not established between the cathodeand theanodee-.g. by the depositing v sodium metal... A device ,whereinuthe vprocess of the invention canbe carried out with the use of anodes of metal alkyl-forming metals of egroups 1I Vto V. of the Periodic Tableris shown iny thek appended drawing., The electrolyticY cell` shown t comprisesv angopening. 1 through which the relectrolyte may.I be introduced while being preferably iii-:molten state. The metal whose metal alkyls are simultaneously formed my be charged .throughA the opening 2 in the form of, fortexample, small spheres or as granules. During the electrolysis, sodium isz deposited as a thin layer on the cylindrical cathode 8 (eg. of` copper) in the middle4 of the electrolytic cell. It flows downwardly and maybe withdrawnl from-.the electrolytic lcell through the opening'. The cathode space is separated from` the ,anodefspace by a ,perforatedcylinderof in,-

sulating material .7 and a superimposed diaphragm.y The latter may,jfor example,` consist. of hardenedlter paper or avfine .cloth or glass filter fcloth. At. the, outside is the anode. space rwhich is-lled withrthesmall metal spheres 11 and may be constantly suppliedA :withfr'esh metal at a rate corresponding to the quantity of metal` dissolved in the electrolysis. This anode space is pro-l vided with twozoutlet` openings-4,16 through-which the metal alkyl formed maybe vwithdrawn depending upon `whether it sinks ,downward in the electrolyte or risesyin as desired while the temperature of the anolyte is ad-l justable by the heatingl element 10 which, in the present case, is operated with circulatingpliquid.

EXAMPLEl 1 In `an electrolytic cell having the vshape of a closed kettle of, glass-lined sheet steel is arranged ink the center a cathodefof sheet. ,copper extended. to .the bottom of the kettle. .t Located on both sides thereof at a distance of about y1 to 2 cm. areV anodeslikewise made of sheet` copperl and beingatleastV 10 to 20cm. shorter than the cathode. A molten mixture of potassium-aluminum tetraethyl and ,20% sodium-aluminum tetraethyl is -lilled intor the kettle under a nitrogenatmosphere., Moreoven: a larger quantity of sodium butoxyjaluminuurtrieth'yl is prepared bythe process of our application Serial No. 792,614, tiled February 11, 1959, now abandoned.

The electrolysis is effected ati 140 C. anda currentI Prior to switching in the density jof about 30 2a./dm.2. current,` a small amount of the ,molten butoxy complex is allowed to flow into the eletcrolyte until its content in They -current is now switched the mixture is about 5%.' on andI sodium butoxyyaluminum triethyl is allowed to `flow continuously into the' electrolyteat a rate of 7.85 gms.` The molten;sodium deposits at the -r cathode .at thevcorrect-rate, i.e. 0.86-y gm. pery ampere- .Y hour.l Itdlows. down at the cathode' and accumulates,y

per ampere-hours.

as a coherent layer at the bottom `of the vessel from which it maybe withdrawn. A 1:1 mixture offe'thylene and ethane is evolved at the anode and a layer Vconsistingof pure butoxy yaluminum diethyl accumulates above `the electrolyte. This layer is easily separated and reconverted into sodium butoxy. aluminum triethyl by means of sodium hydride and ethylene .by the process kdisclosed in our said application .t Serial.l No. 792,614 ,and ,continuously passed to the electrolyte. 1 Carey should betaken in the electrolysis thata certain quantity of the complex sodium butoxy aluminum triethyl is always maintained inf the 'Y electrolyte. Norma1ly',.a very small stationary content will Itis 9 be suicient. However, since the proportioning is not always adjustable to be exactly equivalent to the passage of current due to occasional current fluctuation, it is preferable to operate with a content of a few percent of 'the alkoxy compound in the electrolyte.

EXAMPLE 2 3320 gms. (20 mols) of sodium aluminum tetraethyl are stirred for hours at 150 C. with 740 gms. (10 mols) of potassium chloride. Upon settling of the sodium chloride formed, the formed equimolar mixture of sodium aluminum tetraethyl and potassium aluminum tetraethyl is subjected to electrolysis with a lead anode in the apparatus shown in the figure. The cathode is a copper cylinder. At a distance of 1 cm. therefrom is arranged a perforated cylinder of a material which is not electrically conducting and is not attacked by the electrolyte, such as porcelain or bakelite reinforced by a fabric. The cylinder is surrounded by a diaphragm of hardened lilter paper or of a line cloth or glas lilter cloth. Behind the kdiaphragm is the anode space which is filled with lead spheres and may be supplied continuously with lead spheres at a rate corresponding to the lead dissolved in the electrolysis. Heating of the electrolyte or removal of the current heat evolved during the electrolysis is effected by recirculating a liquid of about 100 C. in the interior of the closed cathode cylinder. Heat supply or removal at the outer cylinder jacket is controlled such that the temperature in the anode space does not exceed 70 C. rEhe temperature during the electrolysis is preferably about 100 C. in the cathode space and about 70 C. in the anode space. The conductivity of the mixture used is 45x10*2 (ohm-cm.)1 at 100 C. The current is adjusted to 20 a. corresponding to a cell voltage of 2 V.

The sodium deposited at the cathode flows down as a thin film at the surface of the cathode into the lower cathode space from where it may be withdrawn from time to time. The eiliuent from the anode space is adjusted such that a reaction mixture containing lead tetraethyl flows off, which is the case when about 500 ml./hr. of liquid are withdrawn from the anode space. The supply of sodium aluminum tetraethyl to the cathode space should be controlled such that the liquid level in the cathode space is about 4 to 5 cm. higher than in the anode space. Yield of sodium: 23 gms. per 26.8 ampere-hours (100% of the theory).

EXAMPLE 3 Molten sodium aluminum tetrabutyl is subjected to electrolysis at 120 C. in the apparatus described in Example 2 using aluminum granules as the anode material. The sodium deposited at the cathode collects at the bottom of the cathode space and may be withdrawn therefrom from time to time. Moreover, the procedure is analogous to that described in Example 2 except that a reaction mixture containing 10% aluminum tributyl is withdrawn from the anode space, which reaction mixture is freed from aluminum tributyl at 100 C. and a vacuum of 0.1 mm. Hg. The yield of sodium is 23 grams per 26.8 amperesxhours, which corresponds to 100% of the theory.

EXAMPLE 4 Electrolysis is effected in the apparatus shown in the ligure and described in Example 2, except that the anode space is not filled with metal granules, but a cylinder of metal wire, e.g. copper, is fastened in the anode space. The electrolysis temperature is 100 C. A melt of the complex compound sodium aluminum triethyl hydride is used as the electrolyte. A current of a. is adjusted at a terminal voltage of 6 v. Under these conditions, 12.8 gms. of sodium (100% of the theory) are deposited per hour at the cathode while hydrogen gas at a rate of 6.3 liters/hr. is evolved at the anode. The supply of sodium aluminum triethyl hydride to the cathode space is adapted such to the efuent from the anode space that a dilference of 4 to 5 cm. is maintained between the liquid level in the cathode space and that in the anode space.

The effluent from the anode space is collected and freed from aluminum triethyl at C. under a vacuum of 1 mm. Hg. The distillation residue may be returned into the electrolytic lcell. The hydrogen evolved at the anode may be used in the regeneration of aluminum triethyl to form complex NaAl(C2H5)3H. The aluminum triethyl is reacted with NaI-I at 100 C. to form sodium aluminum triethyl hydride which may again be charged to the electrolysis.

EXAMPLE 5 The electrolytic cell consists of a cylindrical and internally enamelled steel kettle which contains at the bottom the raw sodium to be reined as a melt. Suspended in the kettle is a cylinder of enamelled sheet steel of somewhat smaller diameter, which is open at both ends and has horizontally tightened across the lower opening a wide-meshed glass ber fabric having a mesh size of l to 3 mm. The net is arranged at a distance of 3 to 5 mm. above the surface of the liquid sodium. Arranged closely above the net is a net of copper or iron wire as the cathode. The electrolysis temperature is C. Sodium aluminum tetraethyl is used as the electroyte. The level of the molten electrolyte must be above the upper edge of the suspended cylinder so that the sodium deposited at the -cathode is surrounded by the electrolyte from above and below. An electrode current density of 20 a./dm.2 can be maintained at a terminal voltage of 2.0 v. The cathodically formed sodium collects above the glass ber net and may be drained from this space from time to time. Care is taken by the addition of raw sodium during the electrolysis that the distance between the anode and cathode is kept constant. T he yield of sodium is 23 grams per 26.8 amperesXhours, 4and 23 gms. of Na were dissolved anodically by the same amount of current. The yield is 100%.

EXAMPLE 6 The procedure is the same as that described in Example 5 except that a mixture of 20% sodium aluminum tetraethyl and 80% potassium aluminum tetraethyl is used as the electrolyte and the same volume of 1% sodium amalgam is substituted for the molten raw sodium. The electrolysis is effected at a temperature of 150 C., a current density of 30 a./dm.Z and a terminal Voltage of 1.5 V. The cathodically deposited sodium collects as a coherent molten layer above the net of glass fiber fabric. To remove the joulean heat and for mixing the electrolyte, a greater electrolyte stock is recirculated through the electrolytic cell while maintaining the liquid in the electrolytic cell at a constant level. This is easily accomplished by allowing an equal volume of electrolyte per unit time to flow from a stock vessel into the space between the anode and cathode as that pumped back into the stock vessel from a point opposite of the inlet opening. The amount of sodium depoisted cathodically after 185 amperesX hours is grams which are drained in molten state from the upper part of the electrolyti-c cell.

The sodium thus obtained still contains about 0.3% of Hg. The mercury content is further reduced when maintaining a temperature of 120 C. during the electrolysis. It is easy to achieve 0.01% of Hg and less in this case. This is that mercury content which, in the production of sodium from sodium amalgam with an electrolyte of molten sodium bromide, iodide and hydroxide, is only achieved after an additional treatment with metallic calcium. The primary mercury content in this prior art process is in the order of magnitude of 1%. Even the last traces of mercury can be removed when repeating the electrolysis in accordance with Example 5.

The Na content of the initial Na amalgam which was 1% has been reduced to about 0.2%. The amalgam is preferably removed from the cell and may be used for ried out with exclusion of moisture and in an inert gasA atmosphere such as, `for example, nitrogen or argon.

What is claimed is: 1. Process for electrolytic production of sodium which comprises:

passing an electrolysis current between an anode and a cathode through an electrolyte comprising a complex compound of the generalrformula MeAlRsR in which Me is alkali metal selected from the ,group consisting of sodium and a mixture of sodium and potassium, R is an alkyl radical and R'. is selected from the group consisting of hydrogen, alkyl, alkoxy,

cycloalkoxy and aroxy, said anode-containing so-A dium, to velectrolyze |sodium from the anode andV deposit sodium at the cathode, the sodium electrolyzed'f at the anode replacing `in the electrolyte sodium de-` posited at the cathode.

2. Process according to claim 1, wherein the anodeis a..sodium amalgam,.the sodium being electrolyredffrom the amalgam without reaction of the mercury.

3. Process.y according to claimZ, wherein the electrolyte contains MeAlRgOR" wherein Me and R are as above and R" is selected from the group consisting of alkyl and cycloalkyl.

4.. Process according to claim 2, the sodium content of the amalgam being less than about 1.5% by weight.

5. Process according to claim 2, wherein the current density is less than about80 a./dm.2.

6. Process according to claim 2, wherein the current density is about 10-50 a./dm.2.

7. Process according to claim 2, wherein the temperature of the electrolyte is about 1GO-150 C.

8. Improvement according to claim 2 in which R is a straight chain alkyl radical containing 2-6 carbon atoms.

9. Improvement according to claim 2 in which Ris a straight chain alkyl radical containing 2 carbon atoms.

1,0. Improvement according to ,claim2 inwhich Me is a mixture .of sodium and potassium and containing up to about 80% potassium. Y

11. 'Improvement according to claim 2 inwhich sai electrolysis is elected'with the sodium 'amalgam as the lowermost layer, the electrolyte as t-he. middle layer, and in which the cathodicallydeposited sodium is kept in suspension by a wide mesh net -of insulating materialzas the uppermost layer.

12. Improvement. according to claim 1 in;which said anode consists of .molten raw sodium.

13. Improvement according to claim 1 inrwhich said anode is a sodium amalgamanode andin which the electrolysis currentzis only passed while ,there is sucient'sodium in the anodematerial toV preventthe formation of mercury alkyls.

14. In the. process for ,the electrolytic production of sodiumv in which an electrolysiscurrent is passed between a cathode andan vanode through asodiumclectrolytein the; formiof a complex compound `of 'the` general formula MnlRgRk in whichlv Me is a metal selected :from the group-consisting. of sodium andmixtures of sodium and potassium, Riis an alkyl radical, andRfis a rnember'seaY lectedfrom the group consisting of: hydrogen, ralkyl, alk-i oxy, cycloalkoxy, and. `aroxy radicals, the improvement which comprises effecting .the electrolysis with a -sodiumcontaining` anode asr'the ,lowermost layer, the electrolyte as the 'middle' layer, and the .cathodically .deposited vs0-V dium kept'in :suspension -by a wide meshed net yof insulating material as the uppermost layer.`

15. Improvement according :to claim '14 vinlwhich said anode is a sodium amalgam anode. v

References Cited by the Examiner UNITED, STATES PATENTS 2,849,349 8/.1958 I Ziegler et al 294-59 2,944,948 7/1960 1 Glrantis 204--59 2,985,568 i 5/1961 Ziegler et al. 204-59 JOHN H. MACK, .Primary Examiner."

WINSTON A. DOUGLAS, `-Examineizy

Claims (1)

1. PROCESS FOR ELECTROLYTIC PRODUCTION OF SODIUM WHICH COMPRISES: PASSING AN ELECTROLYSIS CURRENT BETWEEN AN ANODE AND A CATHODE THROUGH AN ELECTROLYTE COMPRISING A COMPLEX COMPOUND OF THE GENERAL FORNULA MEAIR3R'' IN WHICH ME IS ALKALI METAL SELECTED FROM THE GROUP CONSISTING OF SODIUM AND A MIXTURE OF SODIUM AND POTASSIUM, R IS AN ALKYL RADICAL AND R'' IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKYL, ALKOXY, CYCLOALKOXY AND AROXY, SAID ANODE CONTAINING SODIUM, TO ELECTROLYZE SODIUM FROM THE ANODE AND DEPOSIT SODIUM AT THE CATHODE, THE SODIUM ELECTROLYZED AT THE ANODE REPLACING IN THE ELECTROLYTE SODIUM DEPOSITED AT THE CATHODE.

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