US1585716A - Preparation of sodium - Google Patents

Description

May 25,1926. 1,585,716

P. L. HULlN PREPARATION OF SODIUM Filed Nov. 26, 1923 5 Sheets-Sheet 1 INVENTOR PAUL Lon/ HUL/Af B) w Mzm P. L. HULIN PREPARATION OF SODIUM May 25 1926. 1,585,716 I Filed Nov. 26, 1923 5 Sheets-Sheet 2 Fig.7. n

1 HTTOR/VEYS May 25 1926. 4

P. L. HULIN PREPARATION OF SODIUM Filed Nov. 26, 1923 uwshlrok PHUL LEON M L/N 3 Sheets-Sheet 3 HTTORIVEYJ patented 25, T9226.

rant anon noun, or cnnrronnn, raancn.

STTS

EREPARA'I'ION F SODIUM.

Application filed November 26, 1923, Serial No. 676,887, and in France December 16, 1922.

This invention relates to improvements in electrolytic processes for the preparation of sodium in which this metal is formed in the liquid condition on a cathode made of solid metal from which it becomes detached under the form of molten globules.

Its main application is the production of sodium by electrolysis of a bath of caustic soda (NaOH) in fusion.

The invention may also be applied to the electrolysis of any sodium compounds in molten condition such as the carbonate, chloride, etc., whether they are separately treated or mixed together or whether other suitable materials are added to the same.

In the case of the electrolysis of soda,as noted by Oastner, the production of sodium rapidly diminishes when the temperature of the bath of electrolysis rises; it is therefore necessary that this bath should not be heated much above the melting point of.

soda if it is desired to obtain the best possible output.

The heating produced by the Joule efi'ect is sufliciently regular and adjustable. It is easy to devise the apparatus in such a manner that it suitably dissipates any excess of heat.

But even if the temperature has been maintained below the proper limit, the production of sodium may diminish owing to irregularities or trouble in the operation of the apparatus; this would cause an abnormal rise of temperature and two prejudicial r conditions then arise which aggravate each other and which conjointly act to further reduce the output.

The decrease of the production is thus, sometimes, rapid and considerable.

I have discovered that the main cause of this special trouble is due to the fact that the sodium, formed at this moment, no longer forms a layer adhering on the cathode, but on the contrary becomes detached r from the latter, being divided into fine par ticles scattered throughout the bath where it immediately reacts on OH thus forming hydroxide (NaOH) and at the same time giving off a great amount of heat.

This phenomenon exists in all'apparatus which electrolyze soda in a continuous manner. Its frequency is very variable; it depends on the foreign bodies contained in the electrolyte, on the particular arrangements of the apparatus, on the method of operation, etc.

For remedying this difliculty, various means have been proposed: gitoppages, with or without special cooling, until return to the normal temperature, this being only a momentary remedy. Renewal of the electrolyt'e with complete cleaning of the apparatus, this being costly and laborious. Beplacement of the cathode or periodical pickling of the latter by immersion in water where it resumes its metallic aspect and, with it, its property of giving out again sodlum with a suitable efiiciency.

. This latter process, forming the subject matter of a previous patent of mine is still Although constituting an important im-- provement, said patented process is not easily applicable to apparatus of the Castner type; moreover, in apparatus of large dimensions, the operations for removing,

pickling and inserting the cathodes require somewhat laborious and delicate work, which may cause injury to the cathodes manipulated, losses in soda, etc.

The process and devices forming the subject-matter of my present.- invention are adapted to remedy all these drawbacks. By this invention, I may, without removing the cathode, reestablish the formation of sodium in the form of an adherent layer or of globules sufficiently .massive for resisting the action of the bath tending to detach the sodium from the cathode. I thus obtain an output in sodium higher than by any of the previous processes, as wellas a reduction in the consumption of soda.

The new process consists, substantially, in periodically operating a superficial oxidation of the cathode by causing such cath ode to act as an'anode during a limited time, using for this purpose a very reduced amount of electricity relatively to the amount employed for the electrolysis.

This process can be carried out by means of three main methodsof operation.

1. By reversing the direction of all the current between the anode made of iron (or of nickel or very slightly oxidable alloy) and the copper cathode, during a very short time, say between two and ten seconds.

2. By reversing the direction of the current between the anode and cathode on a considered valuable and is in current use.

. trodes and one or more auxiliary electrodes. The two first methods of operation'can be this branching.

portion only of the electrolyzing current, the other portion being branched from the electrolysis circuit andthe duration of the reversal can be increased in proportionto 3. By momentarily forming special con nections comprising one or. more twin eleccarried outby means of any known or suitable devices.

The third method of operation is carried out by momentarily connecting the cathode with the anode and by causing these two electrodes thus electrically connected. to act as a single anode, or as twin anodes, rela-' tively to another suitable electrode functioning, at that moment, as a cathode common to such anodes. This cathode, which performs its special function intermittently, will be designated hereafter under the name of auxiliary cathode.

After having maintained the cathode in electric connection with the anode during a certain time, this cathode and this anode are caused to resume their independence and their normal function.

It is possible to operate the individualcells or units-of such an apparatus one by one without affecting the others and without sensibly modifying the intensity of the current of the general supply circuit in which the direction of the current can thus remain constant.

. As will be seen hereafter, the invention will improve the operation and efficiency of all the types of apparatus producing sodium by electrolysis.

F or applying this process, the apparatus is furnished with a system of connections and movable contacts, specially combined, by the operation of which the electrodes are 'periodically connected according to the principle which has just been described.

The accompanying drawing illustrates, by way of example, the application on wellknown types of apparatus, of the principles and essential arrangements of the distribution of the current alternately on two cathodes, with the cathode-anode connection, in accordance with the present invention.

In said drawings, Figs. 1, 2 and 3 are vertical sections through an electrolytic cell for carrying out my present invention,

. these three figures differing only as to the iron or nickel or a very slightly oxidizable alloy, on which oxygen evolves, a cathode C preferably of copper (or acopper'alloy) on which are formed at the same time the sodium (liquid) and the hydrogen (gaseous), and a header, receiver or bell D, in which. collected the sodium given off.

The standard Castner apparatus, Figs. 7 and 9, comprises moreover a wire gauze diaphragm F interposed between the electrodes for separating the oxygen from the sodium and hydrogen'which ascend close around the cathode.

Figs. 10 and 1.1 illustrate another apparatus having an immersed cathode provided with such a diaphragm or separator F suspended from the collecting ring D.

lVith each of these apparatuses 1s associated a combination of fixed contact pieces 5, 0, Z, c and of movable contacts h, j, is, the whole forming a switching system of peculiar novel operation.

These contact pieces and contacts may moreover be arranged in a manner other than that shown and they can be spaced apart instead of being arranged in groups.

For these connections and thc se movable contacts any suitable detail arrangements can be adopted, the contacts can be constituted by bars, blades, pins, handles, etc, and use can be made of all the necessary operating accessories which may, if desired, be independent of each other, common to or rigid with each other and even automatic.

The auxiliary cathode is composed of a metallic member immersed in the electrolyte as would be a working electrode.

By way of example, such an auxiliary cathode is shown at E in Figs. 1, 2 and 3.

It is arranged about the anode, but it might occupy other positions. This auxiliary cathode is constituted, here, by a sheet iron ring provided with a current supply conductor i which is connected at its outer end to a terminal or contact piece 6 by which the current is supplied or is interrupted at will.

The working current is supplied. to the anode 13 directly through a conductor a,

without necessity of interposing any switch in the circuit. A branch circuit for this working current is established at f and leads to the contact piece I).

"When the working cathode C is in a period of production, the contacts occupy the position shown. in Fig. 1; the current which till Figs. 1, 4, 7, 10 thus each represent an ipparatus in a condition of normal producion owing to the position of its switching ;ystem.

When the output in metal seems to diminsh, or when the temperature of the bath :ends to rise, or for the purpose of avoiding ;hese objectionable occurrences, normal Working is re-established or ensured by operiting as follows 1 ,r The auxiliary cathode E is caused to be- :ome active by first connecting through-the novable contact j, the contact piece e tothe :o'ntact piece Z, position of Fig. 2. The curcent then branches in the bath by passing, an the one hand, from the anode B to the :athode C and, on the other hand, from the same anode B to the auxiliary cathode E. This position, however, is only a'transitory position adapted to avoid the interruption of the main supply current; It is the position illustrated in Figs. 2, 5, 8 and 11.

The movable contact h is then removed and b is connected to c by means of the contact 70, position illustrated in Figs. 3, 6 and 9; the work cathode C is then connected with the anode B by 57,0, 6, The apparatus comprises therefore at this moment two.

twin anodes emitting together the main current in the mass of the bath towards the auxiliary cathode.

The cathodic-anodic substitution connection allows to obtain on the spot, inthe most practical manner, the superficial oxidation of the working cathode giving the high output which results from this oxidation.

The duration of the oxidizing connection varies with the arrangement of the apparatus, the relative position of the electrodes in action and their dimensions, the intensities ofcurrent which pass through them, the condition of the electrolyte, etc.

One minute will usually be' suhicient for each oxidizing operation with an average of sir: sodium producing operations in twenty-four hours; but it is preferable, in each plant todetermine and to regulate at the beginning, by trials, the duration and frequency whicharc suitable for given apparatuses and electrolytes.

Theoxidat-ion of the cathode is caused to cease and the apparatus to restart its normal operation, by eiiecting in reverse direction the switching movements described above. For this purpose the contact bar 76 is first removed and the bar h is replaced on the contact pieces 0 and Z, so as to thus pass again through the transitory position of Fig. 2. The contact piece j is subsequently removed, 'thus restoring the apparatus, to the position shown in Fig. 1. I

dation of the catho e must be eiiected carefully in order to remain superticiah and without notably corroding this electrode.

This condition is alrea y-ensured' by the principle of the processitself, but it is use.

fully completed by suitable arrangements the two principal ones of which are:

1. The position of the auxiliary cathode outside the anode, this having for its etlect to cause the main mass of the current to pass directly from the anode B to the auxiliary cathode E so much the more as the intensity of the current which passes from the electrode Cto the auxiliary cathode E is,

moreover, reduced owing to the. position of C within B.

The oxidation of the cathode C thus re". mains superficial and uninjurious if care is taken to suitably limit, on the other hand, the. duration of this oxidation.

- 2. The insertion between the contact piece I; and the anodeB (that is to's ay 0n the line 7) of a resistance, which can be a-d justable, through which is limited at will the intensity of the current passing througn the cathode Cduring the operation of oxidation of the latter. It has not been considered necessary to specially illustrate this resistance.

,By means of this regulating device it is possible to reduce at will the rapidity of oxidation of the cathode; this oxidation is thus rendered more regular and prejudicial corrosion is easily avoided. I

These various. means can be employed separately or combined.

An interesting form of carrying out the invention consists in applying certain parts of the apparatuses themselves tothc-intermi'ttent function of auxiliary cathode.- I

The vat A (Figs, 4 and G) is preferably used as auxiliary cathode, this usually rendering unnecessary the special electrode I For that purpose. the vat A (Figs. 4,? and 10) is connected to the terminal or contact piece by a conductor 2' of suihcient cross section, and the most simple and most suitable auxiliary cathode is thus obtainec.

This modification is applicable to most of the apparatus in use in the industry.

The switching operation is ctiected as previously described.

The connections of those of 6, and vice versa, preferably through an intermediate transitory position, Fig. 5, in order to avoid the serious inccn vcniences of an interruption of the main current, this might moreover be obtained by another momentary connection effected at another place. Y .1

it is also possible tense as auxiliary cathode, separately, or preferably combined with the vat, other members such as the sodium Fig. 4 are changed to lid . passes from C to F and from C to D and tori.

receiver D and especially the wire gauze diad of the circuit, as already described, by a contact bar j connecting the contact piece a to the contact piece Z.

Moreover, there is provided a contact piece such as m and a conductor a forming a fixed or variable resistance, connected to the header or receiver D and, by the latter to the wire gauze diaphragm F, which is suspended therefrom.

For effecting the oxidation of the main or working cathode C, by means of these combined auxiliary cathodes(compound auze iliary cathode), the vat A is connected, as already explained, to the contact piece Z by the movable contact j inserted between the contact pieces e, Z (Figs.8 and 11) the con-'- ductor n is connected to e and A by means of a suitable contact such as 0 or any other equivalent contact inserted between m and c (Fig. or m and Z (Fig. 12), after which the blade h is removed and the contact 6 is placed in position. The connections shown in Figs. 9 and 12 are thus obtained.

The current then takes several paths through the bath. The main portion passes from B to E; a fraction passes from B to F and to D. The small fraction of the current which effects the cathodic oxidation and is controlled at will by the resistance a,

The return to the working phase is effected as previously described by bringing back the connections to the positions of Figs. 7 and 10.

The function of auxiliary cathode is carried out in a still simpler manner when the apparatus comprises a system of multiple electrodes opera-ting parallel in group in the same vat.

In this case, for producing the momentary oxidation of one of the cathodes, use can be made as auxiliary cathode of one of the other cathodes in action, or a group of other cathodes, which will thus work with overload during this time.

This modification is illustrated, by way of example, in section and in elevation in Figs. 13 and 14. These drawings will be sufficient for allowing the arrangements and operation to be understood.

The anode is composed of several assembled parallel elements B--B-B-B, which meagre receive through a the current of the main circuit.

In the intervals are arranged the cathodes C, (3 C In the position shown in Fig. 13, which is that of normal working, these cathodesare connected by the contact pieces 0, movable contacts h and contact pieces Z, to the conductor d. For effecting the oxidation of one of the cathodes, the cathodes C for instance (first of the group), the movable contact it is placed in the position b, Fig. 14, this establishing a connection of this cathode with the conductor a. The cathode G then acts as anodeat the same time as the anodes B, thus constituting a partial element of the anodic electrode, and it is these latter anodes B which givepassage to the main mass of the current, all according to the principle of the invention.

During this time, the other cathodes C and C operate together as auxiliary cathode by receiving all the current.

When the cathode to be oxidized has been subjected to this treat1nent,.it is replaced in productive service condition-by the reverse operation which consists of replacing at h the movable contact 7:, this bringing back the apparatus to the position of Fig. 13 which corresponds to normal operation.

The other cathodes are successively treated in the same manner.

Of course this modification does not exclude the possibility of causing any other auxiliary cathode to participate at the same time in the operation, particularly the vat of the apparatus which contains the groups of electrodes.

The principles and means described are of course applicable to all types of apparatus comprising, in any number, multiple electrodes or electrodes composed of assembled elements which can be separated or connected in various ways for effecting the op erations in separate units, in fractions, or in groups, according to numerous modifications which can be realized in the carrying out of the invention.

Moreover, it is possible to insert or use in conjunction with the means described any other means, parts or accessories without changing the principle of the said invention. Besides, the shapes of the apparatus, details, dimensions and certain materials used may be varied according to circumstances and applications.

Claims- I 1. In the production of sodium by the electrolysis of a bath of molten caustic soda with the use of a copper cathode and a slightly oxidizable anode, the step which consists in effecting periodically, with the electrolytic bath itself, a superficial oxidation of the cathode.

2. In the production of sodium by the electrolysis of a bath of molten caustic soda with the use of an oxidizable cathode, the

step which consists in periodically effecting,

in the electrolyzing bath, on said cathode, an anodic reaction by the momentary action in the suitable direction of an amount of electricity limited to the formation of a layer of superficial oxide.

3. In the production of sodium by the electrolysis of a bath of molten caustic soda with the use of a copper cathode and a slightly oxidizable anode, the step which consists in periodically reversing the direction of the electrolyzing.current" between said anode and said cathode, the current flowing during such reversal being limited to about that necessary for the superficial oxidation of copper.

4. In the production of sodium by the electrolysis of a bath of molten soda, the step which consists in periodically effectin on the cathode, in the eleetrolyzing bath, a superficial anodic reaction by the momentary action in the suitable direction of a current the intensity of whichis materially smaller than that of the electrolyzing current.

5. In the production of sodium by the electrolysis of a bath of molten soda, the step which consists in periodically causing the cathode to act as anode, during a limited time under a suitably directed portion of the electrolyzing current, the other portion of this current being deflected and passing outside the cathode treated.

with the aid of an anode, a main cathode,

and an auxiliary cathode, the step which consists in periodically connecting the anode with the main cathode through a resistance, the cathode thus becoming temporarily an anode when the auxiliary cathode is connected with the negative pole of the source of electricity.

-8. In an electrolytic process performed with the aid of a main cathode an auxiliary cathode, and, a third electrode placed between saidmain and auxiliary cathodes, the operation which consists in normally con- 4 Iiecting the negative pole of the source of electricity with said main cathode and periodically connecting the latter with the positive pole while the negative pole is connected wtih the auxiliary cathode to produce a temporary How of current in the opposite direction at the main cathode.

9. In the production of sodium by the electrolysis of a bath of molten caustic soda, with the use of a copper cathode and a slightly oxidizable anode, the step which consists in periodically connecting one of those conducting elements of the apparatus which are in contact with the bath, with the negative pole of the'source of electricity while said cathode is connectedtemporarily with the positive pole." i

10'. In electrolytic processes for the preparation of sodium by the electrolysis of a bath of molten caustic soda, with an electrode consist-in of a plurality of units, nor-' mally functioning as cathodes, and a slight- 1 ly oxidizable anode, the step which consists in temporarily and successively causing said units'to assume anodic it'unctionsto produce the superficial oxidation thereof.

11. In electrolytic processes for the prepa ration of sodium, by the electrolysis ofa bath of molten caustic soda, with a cathode consisting of a plurality of separate electrodes, and a slightly oxidizable anode, that step which consists in temporarily and successively distributing the cathodic charge among certain of said electrodes while the remaining ones are caused to function as anodes to produce the superficial oxidation thereof.

12. In electrolytic processes employing an anode, a main cathode, and an auxiliary cathode which is inactive during-the normal electrolytic operation, the stepwhich consists in periodically connecting the anode with the main cathode so that the latter temporarily assumes anodicfunctions while atthe same time connecting the auxiliary cathode with the negative 'pole'of the source'of electricity. v p

13. In electrolytic processes-employing an anode and a cathodecompos'ed of a plurality of units having independent connections normally. leading to the negative pole of the source of electricity, the step which consists in temporarily disconnecting successively a..

part of said units, from such negative pole, and-connecting them with the anode, while the other units continue to function as a cathode.

The foregoing specification of my im provements in the preparation of sodium signed by me this 14th day of November, 1923.

PAUL LEON HULIN.

Images