US2756140A - Process for recovering alkaline earth metal from admixture with alkali metal - Google Patents

Description

y 24, 1956 A. P. GIRAITIS ET AL 2,756,140

PROCESS FOR RECO'VERING ALKALINE EARTH METAL FROM ADMIXTURE WITH ALKALI METAL Filed Dec. 11, 1952 REACTOR EVAPORATOR 20 I V I9 PRECIPITATOR SEPARATOR ALKALI METAL ALKALINE F ALCOHOLATE EARTH METAL INVENTOR.

ALBERT P. GIRAITIS WILFORD H. THOMAS BY PROCESS FOR RECOVERWG ALKALINE EARTH IVIETAL FRQM ADNWKTURE WITH ALKALI METAL Albert Philip Giraitis and Wilford Harold Thomas, Baton Rouge, La, assignors to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application December '11, 1952, Serial No. 325,458

3 Claims. (Cl. 75-101) This invention relates to the recovery of useful values from mixtures of alkali metals and alkaline earth metals.

Mixtures of the above types of metals are dangerous to handle by reason of their reactivity. At the same time some mixtures, particularly of sodium and calcium, are produced as commercial by-products in large quantities and must be disposed of in some way. Thus, in the production of sodium by electrolysis of a fused bath of sodium and calcium chlorides, the crude sodium as produced is first treated to separate out an accompanying sludge. This sludge is a mixture of metallic sodium and metallic calcium, alone with a minor percentage of salts such as chlorides and oxides.

U. S. Patent No. 2,543,406, granted February 27, 1951, teaches the reaction of mixtures of this type with lower aliphatic alcohols to preferentially dissolve the alkali metal and leave the alkaline earth metal substantially unreacted. This effects a ready separation, and both the alkaline earth metal as well as the alkali metal alcoholate can be recovered as useful products. In conducting this process an excess of alcohol is used so as to insure a complete reaction. Although the process is generally satisfactory for recovering metallic calcium from small batches of electrolytic sludge, some difiiculty has been experienced in the separation step when the operations are carried out on a commercial or semi-commercial scale. It has been observed that when calcium and alcohol are co-present in certain proportions, a violent reaction tends to occur.

7 Although this critical ratio has not been determined with certainty, it has been found that when using methanol as the solvent, for example, if the ratio of alcohol to calcium is permitted to fall to about 1:1, this violent re action may take place, especially if a mixture of this ratio is allowed to exist for any appreciable length of time. Since an excess of alcohol is present in the reaction mixture, it is necessary to pass through this critical range during the separation of calcium from the reactor solution, thereby increasing the hazard to operating personnel and rendering the process commercially unattractive.

Among the objects of the present invention is the avoidance of the above and related disadvantages.

Further objects of the present invention include the provision of a recovery technique which makes possible a safer separation of the alkali and alkaline earth metals.

The above as well as still further objects of the present invention will be more clearly understood from the following description of several of its exemplifications, reference being made to the accompanying drawing in which is schematically shown a flow diagram illustrating some of its essential features.

According to the present invention a mixture of alkali and alkaline earth metals is treated with a lower aliphatic alcohol in accordance with the process described in the aforementioned patent so that'the alkali metal reacts with the alcohol to form alcoholate but the alkaline earth metal remains substantially unreacted. After the reaction with the alkali metal is substantially completed, the reaction mixture is diluted with an inert diluent in which the alcoholate may or may not be soluble but which is inert to the alkaline earth metal and has a boiling point higher than the alcohol. The alcohol is then flashed ofi. from the diluted mixture to leave the alkaline earth metal suspended in the inert diluent. When the alcoholate is soluble in the particular inert diluent employed, the alkaline earth metal can be readily separated from the resulting alcohol-free mixture by filtration or centrifugation. When the alcoholate is not soluble in the inert diluent, the separation of the alkaline earth metal is accomplished by first passing the alcohol-free mixture through a liquid cyclone, sedimentation chamber or some similar classification equipment so as to divide the mixture into two fractions by taking advantage of the difference in specific gravity of the alcoholate and the alkaline earth metal. Since the alkaline earth metal has a specific gravity greater than that of the alcoholate this separation is readily accomplished. The alkaline earth metal is then recovered from the heavier fraction by filtration or centrifugation in either instance not only is the alcohol removed rapidly from the reaction mixture, but the removal is accomplished in the presence of a medium inert to the alkaline earth metal so as to avoid the danger of a violent reaction between the metal and the alcohol.

By lower aliphatic alcohol is meant methyl, ethyl, propyl, or isopropyl alcohol, as well as the various butyl and amyl alcohols. Typical inert diluents suitable for the present invention include pyridine, toluene, xylene, benzene, alkylate, petroleum fractions, mineral oil, kerosene, diphenyl, diphenyl ether, diphenylamine, eutectic mixtures of diphenyl and diphenyl ether (Dowtherm), amyl benzene, decalin, tetralin, a-methylnaphthalene, -5-methylnaphthalene, a-ethylnaphthalene, B-methylnaphthalene, n-decane, n-octane, hendecane, dimethylaniline, aniline, and the like, to mention a few. The choice of diluent to use in a specific instance will depend in part upon the particular lower aliphatic alcohol being employed. When using methanol, for example, any of the inert diluents mentioned above can be used since all have a boiling point above that of methanol; pyridine or toluene is preferred, however, since the by-product methylate is soluble in these materials. When tert-butyl alcohol is used as the reacting alcohol, benzene is unsuitable as the inert diluent since the boiling point of benzene is lower than that of the alcohol although any of the other diluents listed above can be used. Thus, in any particular instance, the only requirements with regard to the inert diluent are that it be chemically inert to alkaline earth metals at temperatures up to about 290 C. and having a boiling point above that of the particular reacting alcohol being employed.

Referring to the drawing, 10 indicates a reactor which need be nothing but a tank. The mixture of alkali and alkaline earth metals can be introduced through line 12, and the reacting alcohol through line 14. In the reactor the combination of materials is maintained under conditions in which the alkali metal is substantially completely converted to alcoholate and dissolved, while the alkaline earth metal is substantially unaffected.

Following the completion of the reaction, the mixture is transferred through line 16 to a mixer shown as a conduit 18 in which it is mixed with an inert diluent of the type described above added by way of line 19 for example. From the mixer the resulting mixture is led to a flash chamber or evaporator 20 where the excess original alco' hol is flushed'otf through line 22 and can be recycled back to the reactortotreat a fresh quantity of mixed metals. Before introducing the recycled alcohol back into the reactor it is condensed either by cooling the line 22 at a point prior to the junction with line 14, or by passing the recycle stream through a condenser (not shown) from which the alcohol is passed to the reactor.

The bottoms of the flash chamber or evaporator 20 are passed through line 24 to a separator 30 which need be nothing more than a centrifuge or filter in those instances where the ,by-product alcoholate is soluble in the inert diluent.

Here alkaline earth metal suspended in the bottom is separated and discharged through line 32 while the balance of the bottoms, which now consist essentially of alkali metal alcoholate dissolved in the inert diluent, are led through line 34 to a precipitator lil. In the precipitator, which can be a standard flash apparatus or conventional distillation tank, the alcoholate is recovered by vaporizing or otherwise removing the inert diluent which is recycled through line 44 back to the flash chamber or evaporator 20. The alkali metal alcoholate is withdrawn .from the precipitator 40 through line 42. The evaporation in the precipitator 40 need not go to complete dryness, but can merely effect a concentration of the alcoholate sufficient to cause an appreciable portion to precipitate shown) in line 44 between the precipitator 40 and the point at which line joins the conduit 18. It is not necessary that the inert.diluent be mixed with the reaction mixture prior to introduction into the evaporator 20. If desired, the fresh diluent along with the recycle diluent from the precipitator can be introduced directly into the evaporator 20 by a line separate from that through which the reaction mixture is introduced.

When the by-product alcoholate is insoluble in the particular inert diluent used, the mixture that is passed from the evaporator 20 to the separator 30 will consist of a suspension of alkaline earth metal and solid alcoholate in the inert diluent. In. this situation the separator 30 will consist of one or more liquid cyclones, sedimentation chambers or similar classification equipment so as to separate the alkaline earth metal from the alcoholate by taking advantage of the diiference in specific gravity of these.

materials. When using a cyclone, for example, the overflow willtconsist of a suspension of alcoholate, in the inert diluent, and the underfiow will consist of a suspension of alkaline earth metal in inert diluent. The overflow is then passed to the precipitator 40 in which the alcoholate is recovered while the underfiow is passed to a filter or centrifuge in which the alkaline earth metal is recovered. The filtrate, consisting essentially of the inert diluent, is recycled back tothe evaporator along withthe diluent from the precipitator 40.

The amount of inert diluent used in carrying out the process of the presentinvention is not especially critical although for efiicient and rapid removal of alcohol from the reaction mixture the volume ratio of diluent to reaction mixture in theevaporator 20 should be at least 1.5 to 1. Also in order to eliminate the necessity of providingextremely precise temperature control in the evaporatr 20 theparticularinert diluent used in a specific instance should havea boiling point which is at least C.

(0.20" C. higherxthan the boiling point'of the reacting alcohol. If desired, theevaporator can also'beoperated at reduced pressure so as to lower the required heating of the mixture.

As one highly effective example of the present invention for the recovery of useful materials from the metal sludge by-product of the electrolytic production of sodium, the lower aliphatic alcoholis methanol, and the reaction is carried out in the manner described in connection with the above-identified patent till the induction period is almost completed, that is, the alkali metal is substantially completely reacted but the alkaline earth metal has not yet begun to react to any appreciable extent. At the end of this time, the reaction mixture consists essentially of sodium methylate, excess methanol and metallic calcium. This mixture is then discharged into conduit 18 where it is mixed with twice its volume of pyridine. The combined mixture is not permitted to stand for atime long enough to exceed the induction period, but is promptly injected into evaporator 20 having a flashing surface maintained at about 100 C. The methyl alcohol promptly flashes off, leaving a thickened slurry of alkaline earth metal suspended in an essentially alcohol-free solution of sodium methylate in pyridine. It is not necessary to use any fractionating head at the evaporator outlet to line 22, inasmuch as the small amount of pyridine that is evaporated off along with the alcohol does not significantly affect the reaction in reactor 10.

A good .yield of alkaline earth metal is realized by merely filtering the evaporator bottoms, and the recovered metal has a purity of about per cent to per cent. Sodium methylate is recovered by passing the filtrate t0 the precipitator wherein the pyridine is volatilized.

Although the invention is described above in connection with a sludge of sodium and calcium prepared in a specific manner, it is equally suitable for mixtures of these metals prepared in any other way, as well as other mixtures of alkali and alkaline earth metals. By way of example,

mixtures of potassium and barium, as well as sodium and magnesium are also readily separated by the above described technique.

As many apparently widely different embodiments of this invention may be made without departing from the .spirit and scope hereof, it is to be understood that the invention is not limited to the specific embodimentshereof except as defined in the appended claims.

We claim:

.1. In aprocess for separating alkaline earth metal from admixture with alkali metal, which process includes the steps of reacting the mixture with an excess of a lower allphatic alcohol to convert the alkali metal to alcoholate without significantly attacking the alkaline earth metal, the combination therewith of the improvement which consists .of separating thealkaline earth metal from thelreaction mixture by first diluting this mixture with at least 1.5 times its volume of an inert diluent which is inert to the alkaline earth metal and has a boiling point higher than the alcohol, flashing off the alcohol from the diluted mixture to leave the alkalineearth metal suspended in saidinert diluent, and, separating the alkaline earth metal from the said inert diluent.

2. In a process for recovering values from sludges of .calcium mixed with sodium, which process includes the steps of reacting the sludge with excess methyl alcohol to cause the sodium to be substantially completely converted to alcoholate withoutappreciably attacking the calcium,

the combination therewith of the improvement which consists;of diluting the resulting reaction mixture with at least 1.5 times its volume of pyridine, flashing ott the ex- .cess methanol from the diluted mixture to leave a suscess of a lower alphiatic alcohol to convert the alkali metal uent, said inert diluent being present in an amount at least to alcoholate without significantly attacking the alkaline 1.5 times the volume of said reaction mixture and being earth metal, the combination therewith of the improveinert to the alkaline earth metal and having a boiling point ment according to which the alkaline earth metal is sepaat least 10 higher than the boiling point of said alcohol. rated from the reaction mixture by introducing said mixture 5 into an inert diluent maintained at a temperature higher References Cited in the file of this patent than the boiling point of said alcohol so as to efiect a UNITED STATES PATENTS substantially instantaneous flashing of said alcohol and leave the alkaline earth metal suspended in said inert dil- 2,543,399 Callngaen 1951

Claims (1)

1. IN A PROCESS FOR SEPARATING ALKALINE EARTH METAL FROM ADMIXTURE WITH ALKALI METAL, WHICH PROCESS INCLUDES THE STEPS OF REACTING THE MIXTURE WITH AN EXCESS OF A LOWER ALIPHATIC ALCOHOL TO CONVERT THE ALKALI METAL TO ALCOHOLATE WITHOUT SIGNIFICANTLY ALKALINE EARTH METAL FROM THE REACTION COMBINATION THEREWITH OF THE IMPROVEMENT WHICH CONSISTS OF SEPARATING THE ALKALINE EARTH METAL FROM THE REACTION MIXTURE BY FIRST DILUTING THIS MIXTURE WITH AT LEAST 1.5 TIMES ITS VOLUME OF AN INERT DILUENT WHICH IS INERT TO THE ALKALINE EARTH METAL AND HAS A BOILING POINT HIGHER THAN THE ALCOHOL, FLASHING OFF THE ALCOHOL FROM THE DILUTED MIXTURE TO LEAVE THE ALKALINE EARTH METAL SUSPENDED IN SAID INERT DILUENT, AND SEPARATING THE ALKALINE EARTH METAL FROM THE SAID INERT DILUENT.

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