US1597231A - Electrolytic production of alkali metals - Google Patents

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Aug. 24 1-926.

O P.E.HAYNES ELECTROLYTIC PRODUCTION OF ALKALI METALS Filed March 25} 1922 I especially a Patented Aug. 24, 1926.

UNITED STATES Y 1,591,231 PATENT OFFICE.

PIERRE E. HAYNES, OF BUFFALO, NEW YORK.

ELECTROLYTIC PRODUCTION OF ALKALI IETALB.

Application filed Iarch 23, 1922. Serial Io. 545,918.

The chief object of this invention is to provide a process for the manufacture of alkali metals, particularly sodium, potassium and magnesium, whereby such metals may be produced in greater purity and'at a higher eiiiciency than by present methods.

The alkali metals are now commonly made by the electrolysis of molten or fused solutions of their compounds. The chief difliculty of the present processes is the protection of the metal from atmospheric oxygen and nitrogen as well as from some of the byproducts of the electrolytlc decomposition itself.

My invention in its preferred form consists in electrolyzing molten compounds containing the desired metal, removing some or all of the products including the metal as vapors and afterwards condensing the metal se arately.

aking magnesium as a specific exam le, fused carnallite or any suitable compoun of magnesium is melted and electrolyzed at a suitable temperature, preferably above 650 degrees centigrade, in an air-tight vessel capable of withstanding an external pressure of, say, one atmosphere or more. The

nmgnesium will evaporate if the internal pressure is reduced to less thanone inch of mercury, and the evaporation is at a sufli cie'nt rate to remove it from the solution rapidly. It will of course evaporate at a lesser rate if the pressure in the cell is great- At the lower pressure, however, the reaction between magnesium and various gases is greatly reduced in intensity due to the greater attenuation of the gases andmagnesium vapor. The result is a larger yield of metal and the occlusion of less of these gases in the metal produced.

Sod1um, ota ssium, and magnesium are dhpted to treatment by this process on account of their low melting and boiling points. The generally accepted melting and boiling points of these materials are as follows:

Each of these metals is easily va orized at several hundred degrees below its oiling point if the pressure 1s sufliciently reduced.

Apparatus convenient and suitable for practicing the inventionin the preferred manner "is illustrated diagrammatically in the accompanying drawing, in which the a paratus is shown partly in section.

Referring to the drawin ,1 is a closed electrolytic cell partially fil ed with a molten electrolyte 2 containing one or more compounds of the metal desired. The electroyte is separated into two ortions near the surface by a porcelain or ot er suitable hood or partition 3. Upon subjection of the mass to a direct or continuous current between cathode 4 and anode 5, preferably composed of iron and carbon, respectively, the metal is produced around the cathode and certain gaseous by-products are generated around the anode. The gaseous portions of the anodic products are withdrawn through valved pipe 6 by vacuum pump 7. Due to the low specific gravity of the metallic prodnot it rises to the surface of the molten liquid around cathode 4 and there vaporizes. The vapors are withdrawn through valved pipe 8 to condenser 9 which is exposed to the coolin effect of the atmosphere or any other heat a sorbing medium. The vapor of the metal withdrawn into condenser 9 by the vacuum pump 7 acting through pipe 10 is liquefied and falls into receptacle 11 which is removably attached to condenser 9. The liquefied metal product is retained in receptacle ll until'the end of the run and is then recovered by detaching receptacle 11 at thepoint 12 and withdrawingthe roduct in either the liquid or solid con ition.

Where an extremely low pressure is attainable or where an extremely pure metal is not desired, the hood 3 may be dispensed with and all of the products of the electrolysis drawn through pipe 8 and condenser 9 where the metal will be deposited by condensation and the uncondensed vapors withdrawn through pipe 10 by vacuum pump 7.

Some additional heat may be required for the evaporation of the metal product and it is therefore desirable in some cases to utilize'more or less of the heat of condensation to maintain or aid in maintaining the temperature of cell 1, or to su ply this extra heat by the use of suita le auxiliary means. As indicative of the latter method a gas burner is shown at 13.

The use of a vacuum electrolytic cell not only excludes air but as previously stated diminishes the occlusion of the gases by the metal and the recombination of the gases .and metal. Both these results are believed chlorid from sea water or terrestrial brines,

sponding potassium compounds are also usacommonly known as bittern. These residues nearly always contain all the alkali metals. For the manufacture of sodium it is also ssible to use sodium hydroxid, sodium carnate or sodium nitrate, and the correbio for makin that metal, but at present their cost is in gpneral prohibitive. In some cases, especia y when using naturally occurring mixtures containing the salt or salts, it is desirable to add one or more substances to obtain a suitable or advantageous melting point or prevent side react-ions. Among the substances suitable for such purl pose may be mentioned sodium chlorid, so-

ium sulfid, ammonium chlorid, and calciumfluorid. It is generally desirable to operate at a rather higher temperature than has commonly been emplo ed heretofore, in order to get the increase vapor tension which is'an advantage in the present process but which in the past has been a source of loss and'annoyance.

The voltage-and current employed may i varyconsiderably', depending upon the usual factors, such as the resistance of the bath; the size of the cell and the effectiveness of the heat-insulation. used with it, if any; the amount, of heat supplied from. an external source, if any; etc. Hence no general rule A asto voltage and current can be given. It

maybe stated, however, that formaking magnesium fromcarnalhte with extraneous .heat, a voltage of 501- 6 volts is sutficient, l with a current densityof from 10 to 15 amtraneous heat it is generally desirable to operate with 8 to 10 volts or higher and 40- or more amperes persquare decimeter.

. atmospheric.

a temperature above the melting point of the metal, and withdrawing the anodic and cathodic products in vapor or gaseous form at less than atmospheric pressure.

3. A process for the production of metals, comprising electrolyzing a molten bath containing a compound of the metal desired, at a temperature above that of the melting point of the metal, and withdrawing the anodic and cathodic products in vapor or gaseous form separately at a pressure less than atmospheric.

41. A process for the production of metals, comprising electrol zing amoltenbath con taining a-compoun of the metal desired, at a temperature at which the metal has an appreciable vapor tension, and withdraw ing the anodic and cathodic products in vapor or gaseous form, at a pressure below 5. A process for the production of metals,

comprising electrolyzing a molten bath containinga compound 0 the metal desired,

at a temperature at which the metal has an appreciable vapor tension and withdrawing the .anodicand cathodic products sepa- I rately in vapor or gaseous form at a pressure below atmospheric.

6. A process for making magnesium, com-- prising electrolyzing a fused salt of magnesium at a temperature sufiicient to vaporize themagnesium produced, withdrawing the anodic and cathodic products separately in vapor or gaseous form, and condensing the magnesium vapor so withdrawn.

In testimony whereof I hereto afiix my signature.

PIERRE E. HAYNES.

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