US2480655A - Process for the production of alkali metal - Google Patents

Description

Aug. 30, 1949. (3. B. JACKSON ET AL 2 0,

PROCESS FOR THE PRODUCTION OF ALKALI METAL Filed Sept. 13, 1946 7 Na K (on K)VAPOI2,

\1 CONDENSATION Na K ALLOY (012 K) MOLT'EN KCI HEAT Na VAPbR I NaCl SLAG WITH Na k HEAT HEAT NaCl SLAG INVENTORS. 04257 a. JHCAJON, a CUGTNESSES 8 ER. dwi ffy z; 44, 7

A 7' Tole/vars.

Patented Aug. 30, 1949 SafefniApnlianoes-Company, Pittsburgh, Pa., -oorporation:.of Pennsylvania Amill lfatib'mseptbmlier 13, 1946, SCIiE'tINO. 696L918 fi elaims.

This inventionrelates to fiKE 'p'HJ'GHGtMH of po tassium= aswellas soiiium potass'ium alloys:-

It has been: roposed heretofore to produce sodium-potassiuin alioys' byreacting a potassium compound, such as the hydroxide '(KQH), the carbonate (K zCOziy or tfie'clilbride KGL), with elemental sodium to'prodhcea sodium-potassium alloy and a compound of sodium -and' the anion of the potassiumcompound used. Thatmay be accomplished either by -abatch process or by a continuous process in "whith -thmpotassium-compound is introduced colitinuously intb an inter-'- mediate" point of anappropriate oollimn and sodiumvapor is introduced at 'a point hel'ow' the entry of the potassium compound; Whether practiced by' the batchor the continuous pro"- cedure, the reactionconditibiisaccordingto prior proposals and practice-"haVQBeBn such that although the sodium potassium allo'y is produced satisfactorily; the proeecl'ure' 'has not been=economical because for desirahle opera-tine conditions an excess of thepot'a'ssium compound; such as potassium chloride, overtfiat-theoretically neces'sary has been used-'- with the-result" that the slag has consisted for'the greater part 'o'f potas sium' chloride. That has'heen undesirable because the'slaghas little or noutiiity; and its'major content ofpota'ssium chloride; which is relativelyexpensive; thus represents a'Ioss; or viewed otherwiseit isa majoritenr of the cost hurdenof the alloy.

It has been proposed also to operatethe-foregoing continuous procedure-"hr such manner as to fractionate the-alloy produced, wherehy pure, or substantially pure, potassium is recovered as is advantageous for-some purposes: "Flie'foregoing disadvantage has, however; equally attended such a fractionation= procedure:

Theprima-ry object-of thepresent invention is to provide a continuousprocess of'the foregoing type that results 'ina slag ofvery low contentof potassium compound and "is thus; suhstantially more economical t'han prior practiees; and which is readily performed and doesndtobjectfonahly alter or complioate'the-lmownprocedures and app aratu'stherefor.

other obiectswilf 'beunderstood from the fol"- l'owing specification;

The accompanying drawing is a flow sheet" illustrative of oufiiew method, :partbeing broken away'for clarityof illustration;

In accordanee with "the present invention a potassium compoun'd 'reducihle hy sodium- (Na);

*it-amipringthe melttoatemperature somewhat 2. above: themeltingj point,- and' it: is then fed into an intermediate point oft a column; or tower; :pro vided with appropriate packing. Sodiumvisrvae porized and fed into the. column. at arpointibelow the point of entry of" the potassiumcompound, suitably substantially at: the: bottom of the. tools umn. As the. molten potassium compoundtfiows downwardly through the; column it will. react with the upwardly rising-sodium: vapor. and thereby form a mixture of: vapors ofzsodiumiand potasslum that may be withdrawnifroma the-upper end of the column and condensed to obtainsodiu'mpotassium alloy, or, if preferred; the column may be operated in such manner'asitoi effect ffraotionation of the alloy; to? recover substantially pure potassium. Thesla'e"that isfor-med a result of the reaction between the. potassiumzcome pound and sodium flows to the. bottom of the column and is withdrawn.

We have discovered, and: it"is upon this; that our invention is in largezparti'predicated that substantial economy with no interference.- operation or with recovery ofi the desired& alkali metal or alkali metal alloy; isztohe had by: passing theslag from the 'botto'mrof: the-.co'lumntd'a receiver, or re-boilenwhereit is? held while subajecting it to heat to drive-off thersodiumithatzthe slag normally carries with it. The sodiimrreecovered in this way is then' disposed of appropriately, most suitably by returning it toi the'coleumn. In this way we e'ifect recovery of sodium that would normally be lost: in the. slag; and we are enabled to operate the. column so: thatthe slag as finally discharged is'composedp redomi nan'tly of sodium compound; Thisris-ini striking comparison with prior practicerir-rwhiolr, torepeat, the slag was composed predominantlyflof potassium compound.

In the preferred practiceofi'thepresentinvem tion the sodium that is to be supplied-to the coi umn' islikewise introduced into: the. ire-boiler in an amount such as to form a layeroverlying the slag, and the re-boiler' is heated itoisu'ch a temperature as to vaporize the"sodium;- whichxis then passed to the column. In this way we avoid separate heating of a source-=ofsodium to supply vapor to the column, andat 'the salinev timetlie supernatant sodium layer ispresent=to=receivethe sodium recovered from the slag:

Having reference nowto -'the drawing,: which illustrates-the preferred emb'od'imeritioiitheihven- 'tion with reference to the use ofipotass'iunn clnoride, molten potassium chloride; suitably at a temperature of about rare is' fez'i". to a I provided with suitable packing materlals'ssuoh as stainless steel rings 2. Sodium vapor is introduced in the bottom of the column and rises upwardly therein countercurrent to the downwardly flowing molten potassium chloride. The two react to form elemental potassium and sodium chloride. The column is heated, as indicated in the drawings, to a temperature that is dependent upon the product to be recovered. Thus, if a sodium-potassium alloy is desired the column is heated so that its contents will be at a temperature somewhat above the boiling point of sodium, say to about 1620 F., whereby both sodium and potassium are vaporized and rise to the top of the column from which the mixed vapors may be withdrawn and condensed.

The salt slag that is formed flows downwardly to the bottom of the tower. In accordance with the present invention this slag is withdrawn and passed to a suitable closed receiver 3 of such size that the slag is retained for a substantial period of time before being discharged. Receiver 3 is heated to a temperature at least suillcient to maintain the slag molten and boil ofi the sodium that the slag carries with it, that is, to at least about 1620 F. From receiver 3 the slag is passed, 1

preferably, to a trap t which is likewise heated for the purpose of driving off any traces of residual sodium that may remain in it. The sodium-free slag is then discharged from the trap 4, for instance into receivers in which it is allowed to solidify for disposal.

Preferably also, the sodium supplied to column I is introduced into receiver 3 to form a layer of substantial thickness that overlies the slag that is held in the receiver. Inasmuch as the slag is at a temperature above the boiling point of sodium, the metal is vaporized and fed to the column, as shown.

Desirably, an inert gas, such as nitrogen, is supplied to the system, as indicated in the drawing, to keep it under a pressure slightly in excess of atmospheric.

A further and important factor resides in our discovery that the rate of addition of the reducible potassium compound, e. g., KCl, constitutes an important factor. We believe now that the exchange reaction, between sodium vapor and the potassium compound, occurs over a relatively narrow zone adjacent the point of entry of the potassium compound. If the temperature immediately below that point be determined in relation to the slag composition it is found that better, i. e., more complete, reduction is obtained with increasing temperature. Based upon this we have found that the best results are to be had by controlling the rate of addition of the potassium compound so that a high concentration of sodium vapor will be present in the reaction zone, which is confined thereby to a small zone toward the mid-length of the column. For example, when KCl is used it enters the column at about 1550 F., and in accordance with this feature of our invention it is fed at a rate such that the temperature midway of the column is maintained between about 1575 and 1585 F., for optimum operation. If the rate of feed be increased, the mid-column temperature will fall to about 1550 F., and a high yield based on the exchange reaction will not be obtained. This is not due to change in equilibrium with temperature but rather is due to a lowered relative concentration of sodium vapor. Hence we prefer to feed the potassium compound at a rate such that there is a high concentration of sodium vapor with the reaction occurring over a narrow zone.

We find that in this way we can produce more economically a sodium-potassium alloy at least comparable in all respects to that produced in accordance with prior proposals and at the same time a slag that is both essentially free from sodium and which also consists predominantly of sodium chloride .(NaCl). .For example, in continuous operation the slag discharged from trap 4 consists of about per cent, and there may be as much as per cent, of sodium chloride, with the remainder potassium chloride. This is in direct contrast with previous procedures in which the slag produced commonly contains about 75 per cent of potassium chloride and 25 per cent of sodium chloride.

Although the invention has been described in detail with reference to the production of sodiumpotassium alloy, it will be understood that pure, or substantially pure, potassium can be recovered instead of the alloy byjappropriate operation of the column. Thus, pure potassium boils at atmospheric pressure atabout 1420" F., and by appropriate control of the temperature gradient within the column, pure potassium may be withdrawn from the top.

We prefer to operate our process substantially at atmospheric pressure because although operation under vacuum would permit the use of lower temperatures, any advantage gained thereby would be more than ofiset by the added cost of apparatus strong enough to withstand the vacuum coupled with the ever present danger of collapse of some part of the apparatus, or of leakage of moisture into the system with disastrous results. Moreover, the melting point of potassium chloride is approximately 1420" F. and consequently ii the pressure in the system-is lowered to any extent, as would be necessary to gain advantage from operation under reduced pressure, or vacuum, the sodium vapor from the receiver, or reboiler, 3 would not be hot enough to keep the potassium chloride in a liquid state, which is essential.

According to the provisions of the patent statutes, we have explained the principle and mode of operation of our invention and have illustrated and described What we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. That method which comprises the steps of continuously passing a molten potassium compound reducible by-sodium to a reaction column operated under substantially atmospheric pressure, continuously passing sodium vapor into said column at a point below the entry of said potassium compound, and thereby forming a sodiumpotassium alloy and a slag composed predominantly of sodium and the anion of said potassium compound, withdrawing alkali metal comprising potassium from the upper end of said column, withdrawing said slag from the lower end of said column and passing it to a closed chamber, heating the withdrawn slag in said chamber to vaporize sodium carried by it, and returning the thus vaporized sodium to the column.

2. A method according to claim 1, said alloy being fractionated'in said column above the point of entry of said potassium compound to produce substantially pure potassiunnand withdrawing said potassium from the upper end of the column.

3. A process comprising the steps of passing potassium chloride and sodium vapor continuously and counter-currently in a reaction column operated under substantially atmospheric pressure to produce sodium-potassium alloy and a slag composed predominantly of sodium chloride,

said sodium vapor being supplied to said column from a container in which a body of liquid sodium is heated to at least the boiling point of sodium, withdrawing said slag from said column and passing it through said container to vaporize sodium carried by the slag and to effect further reaction between the sodium and residual potassium chloride in the slag and returning the thus vaporized sodium and recovered potassium to the system, and withdrawing alkali metal comprising is driven to the right, thereby forming a sodiumpotassium alloy and a slag composed predominantly of sodium and the anion of said potassium compound together with a minor amount of said potassium compound and sodium metal, withdrawing alkali metal comprising potassium from the upper end of said column, withdrawing said slag from the lower end of said column and passing it to a closed chamber, heating the slag in said chamber to at least about 1620 F. to vaporize sodium carried by the slag and to eiTect further reaction of sodium with residual potassium chloride carried in the slag, and returning the thus vaporized sodium and the recovered potassium to the column.

5. That method which comprises the steps of continuously introducing sodium vapor from a closed chamber heated to at least about 1620 F. into the lower end of a reaction column operated under substantially atmospheric pressure, con tinuously introducing molten potassium chloride at a temperature of about 1550" F. at an intermediate point of said column to produce and maintain adjacent thereto by reaction with said sodium vapor a temperature of about 1575 to 1585 F., thereby forming a sodium-potassium alloy and a slag of sodium chloride and not over about 10 percent of potassium chloride together with a minor amount of metallic sodium, withdrawing alkali metal comprising potassium from the upper end of said column, withdrawing said slag from the lower end of said column and passing it to said closed chamber, heating the slag in said chamber to vaporize metallic sodium and to effect reaction of residual potassium chloride carried by the slag, and returning the thus vaporized sodium and recovered potassium to the column.

6. A method according to claim 5, said alloy being fractionated in said column above the point of entry of said potassium chloride to produce substantially pure potassium, and withdrawing said potassium from the upper end of the column.

CAREY B. JACKSON. ROBERT C. WERNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,872,611 Thurm Aug. 16', 1932 FOREIGN PATENTS Number Country Date 134,680 Switzerland Oct. 16, 1929

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