Process for producing alkali metals in elemental form

A process of producing alkali metal by a reduction of alkali metal compounds with metallic reducing agents, which is simplified and avoids corrosion of the reaction vessel and part thereof in that the reduction is effected with particulate magnesium in an organic solvent which under the conditions of the process is inert to the alkali metal to be produced. The reaction is effected at temperatures from 100.degree. to 300.degree. C. In an embodiment of the process the reduction is effected in the presence of an alcohol used as a reaction accelerator.

FIELD OF THE INVENTION 
Our present invention relates to a process for producing alkali metals in 
elemental form by a reduction of corresponding alkali metal compounds with 
metallic (elemental) magnesium. 
BACKGROUND OF THE INVENTION 
It is known that particularly potassium metal can be produced by 
thermochemical processes (German Patent Publication No. 19 32 129). The 
starting compounds used for that purpose are mainly potassium halides, 
potassium carbonate or potassium hydroxide and the reducing agents used 
are mainly coal, calcium carbide, aluminum, magnesium, silicon or 
ferrosilicon. 
In the process disclosed in U.S. Pat. No. 2,480,655, potassium metal is 
produced by a reduction of molten potassium compounds by means of sodium 
metal. Such processes can be carried out only at high temperatures in the 
range from 500.degree. to 1300.degree. C. and it may be necessary to use a 
reduced pressure. 
Processes which comprise melting involve a high energy consumption and 
require equipment consisting of special materials, such as stainless 
steel. 
OBJECT OF THE INVENTION 
It is an object of the invention to provide for the production of alkali 
metals an improved process which can be carried out in a simple manner and 
without requiring molten phases during the formation of the alkali metal. 
DESCRIPTION OF THE INVENTION 
In a process of producing alkali metals by a reduction of alkali compounds 
with a metallic reducing agent, this object is accomplished in accordance 
with the invention in that the reduction is effected with particulate 
magnesium in a solvent which under the conditions of the process is inert 
to the alkali metal to be produced. 
The organic solvents which are nonreactive with the alkali metal to be 
produced include saturated aliphatic or cycloaliphatic hydrocarbons, which 
particularly have 8 to 20 carbon atoms in straight or branch chains or in 
cyclic form, such as decane, undecane, dodecane, decahydro-naphthalene, 
also commercially available special gasolines having boiling ranges 
between 150.degree. and 250.degree. C., such as Shellsol T, Shellsol D 70, 
kerosene. Said special gasolines have, e.g., a composition of 5% 
naphthenes, 3% n-paraffins, 92% isoparaffins or a composition of 40% 
naphthenes, 30% paraffins, 30% isoparaffins. 
Magnesium is used as the metallic reducing agent. The magnesium is suitably 
employed in granular or powder form, particularly in the form of turnings. 
In the selection of the particle size or fineness of the magnesium metal a 
possible increase of the reactivity of the system owing to a higher 
hydration water content of the alkali metal hydroxide must be taken into 
account. 
Starting compounds for the alkali metal to be produced, such as sodium, 
potassium, rubidium or cesium, include particularly the hydroxides or 
alkoxides of the alkali metal. 
The reduction of the alkali metal compounds to form the metal may be 
described by the following illustrative reaction equations: 
##STR1## 
where HC represents the inert solvent, ROH a possible alcohol or 
alcoholate reaction promoter. 
If the hydroxide contains hydration water, a dehydration, which is violent 
in case of a high hydration water content, is initiated by the magnesium 
with formation of hydrogen and magnesium hydroxide or--at higher 
temperatures--of magnesia. 
The reduction is preferably effected in the temperature range from 
100.degree. to 300.degree. C., preferably from 150.degree. to 250.degree. 
C., under normal or increased pressure. The reduction time is about 1 to 8 
hours. To carry out the process in accordance with the invention the 
starting components, such as potassium hydroxide or potassium alkoxide, 
are charged together with particulate magnesium, e.g. magnesium chips, 
into a reactor, which may be pressure-resistant and which has previously 
been supplied with the inert organic solvent. The reactor is provided with 
heating means, a stirrer, a reflux condenser and means for supplying inert 
gas. 
Where alkali hydroxides are used, it has proved suitable to accelerate the 
reaction by an addition of alcohol or alcoholate. Preferred reaction 
accelerators are alcohols having 3 to 8 carbon atoms, such as propanol, 
butanol, pentanol, particularly tertiary butanol or tertiary pentanol, or 
the corresponding alkali metal alcoholates. 
In the inert solvent the reaction mixture forms a dispersion having a 
solids content of about 20 to 25% by weight. The alkali metal compounds 
and the magnesium metal are used in equimolar quantities. Any reaction 
accelerator will be used in a quantity of about 5 to 10 mole percent of 
the quantity of the alkali metal hydroxide. 
The alkali metal which has been formed may be separated by processes known 
per se, such as distillation, filtration or gravity separation with 
solvents having a suitable density. 
The advantages afforded by the process in accordance with the invention 
reside in that the alkali metals can easily be produced at relatively low 
temperatures, the reactor employed may be structurally simple and consist 
of inexpensive materials, and corrosion will be avoided.

SPECIFIC EXAMPLES 
The invention will be explained more in detail with reference to the 
following Examples. 
EXAMPLE 1 
Production of Potassium Metal From Potassium Hydroxide 
This Example concerns the production of potassium metal in a general 
process and experimental setup which can be used also to produce other 
alkali metals. 
In a 1-liter four-neck flask, 31.1 g (1.278 moles) magnesium chips, 61.2 
potassium hydroxide (1.000 mole kOH, 0.278 mole H.sub.2 O) and 500 ml 
Shellsol D 70 are heated to the boiling point of the solvent. At a 
temperature of about 100.degree. to 130.degree. C., a violent evolution of 
H.sub.2 is initiated (about 1 liter/min). 278 millimoles H.sub.2 have been 
evolved after 1 hour. The rate of gas evolution distinctly decreases 
toward the end of that time. 
At the boiling temperature (about 200.degree. C.), about 6.0 grams tertiary 
butyl alcohol (80 millimoles) dissolved in 6 g Shellsol D 70 are slowly 
added in drops within half an hour. 80 millimoles H.sub.2 are evolved. 
Under constant stirring, the evolution of H.sub.2 (total 460 millimoles) 
and the formation of potassium metal are continues and are terminated 
after about 4 hours. 
This is succeeded by cooling to 70.degree. C. with stirring. Then the 
stirrer is stopped and the cooling is continued under an argon atmosphere. 
Until the colorless reaction solution is cold, white magnesia and a 
regulus of potassium metal have settled to the bottom. The solvent is 
subsequently distilled off under a vacuum (p=1 torr) or is filtered off. 
200 ml 1,4-dioxane are then added to the residue at room temperature, 
followed by heating to 60.degree. to 100.degree. C. As a result, the 
potassium rises to the surface and is comminuted by stirring to form 
spheres of suitable size. When the desired spherical shape has been 
achieved, the stirrer is stopped and the contents of the vessel is 
permitted to cool. The reaction product mixture is then transferred to a 
separating vessel and is washed with dioxane. When the magnesia has 
settled, the vessel is drained to separate the potassium from the MgO and 
dioxane. The potassium is then melted on a filter medium and is sucked 
under a slight vacuum into a flask. Potassium having a silvery luster is 
obtained in a yield of 34.0 g, corresponding to 87% of theoretical yield. 
The dioxane-MgO suspension is filtered at room temperature through a frit. 
The residue consisting of MgO is dried in a vacuum at room temperature. 
The dioxane is completely recovered from the filtrate by distillation. A 
residue is left, which consists of potassium tertiary butylate, which has 
been formed by the reaction of the tertiary butyl alcohol. 
EXAMPLE 2 
Production of Sodium Metal From Sodium Hydroxide 
In a reactor as described in Example 1, 40.9 g (1.023 moles) sodium 
hydroxide, 25.2 g (1.037 moles) magnesium chips and 9.7 g (0.101 mole 
sodium tertiary butylate in 314 g Shellsol D 70 are reacted at the boiling 
temperature of 210.degree. C. with stirring for 15 hours. The solvent is 
subsequently removed by vacuum distillation (120.degree. C., 20 millibars) 
and is thus completely recovered. 350 g dioxane are added to the residue 
and the resulting mixture is heated to the boiling point with stirring. 
When the sodium has the desired particle size, the stirrer is stopped, the 
dispersion is permitted to cool and the sodium metal which has risen to 
the surface is skimmed off. Yield: 19.8 g (84% of theoretical yield). 
EXAMPLE 3 
Production of Potassium Metal From Potassium Alcoholate 
In the reactor described in Example 1, a mixture of 74.8 g potassium 
tertiary amylate (0.59 mole), 7.3 magnesium chips (0.3 mole) and 400 ml 
decalin is heated with stirring at 150.degree. C. for 3 hours. A regulus 
consisting of 15.1 g (0.38 mole) potassium is recovered from the cold 
reaction product mixture. Yield: 65.5%. 
EXAMPLE 4 
Production of Sodium Metal From Sodium Alcoholate 
In the reactor described in Example 1, a mixture of 19.24 g sodium tertiary 
butylate (200 millimoles), 2.48 g magnesium chips (102 millimoles) and 150 
ml Shellsol D 70 is reacted with stirring and refluxing for 1.5 hours. 
From the cold reaction product mixture, a sodium regulus with adherent 
magnesia is recovered and is cleaned by filtration at 100.degree. C. 
through a frit. Sodium yield: 1.2 g (25% of theoretical yield). 
EXAMPLE 5 
Production of Cesium Metal From Cesium Hydroxide 
In the procedure described in FIG. 1, a mixture of 32.5 g cesium hydroxide 
(217 millimoles), 5.4 g magnesium chips (220 millimoles) and 300 ml 
undecane are heated with stirring at the boiling temperature of 
196.degree. C. in the procedure of Example 1. 1.6 g (22 millimoles) 
tertiary butanol dissolved in undecane are then added in drops during 25 
min and the contents of the reactor is heated with refluxing for 
additional 13 hours (H.sub.2 O evolution: 22 millimoles). After cooling to 
temperatures below the melting point of cesium, the reaction product 
mixture is poured onto a fine-mesh sieve to separate cesium regulus having 
a silvery luster from the magnesia. When the molten cesium has been 
filtered through a frit, the pure metal is obtained in a yield of 11.2 g, 
corresponding to 39% of theory. 
EXAMPLE 6 
Production of Cesium Metal From Cesium Alkoxide 
In a reactor as described in Example 1, 69.6 g cesium hydroxide (443 
millimoles CsOH, 176 millimoles H.sub.2 O) and 18.0 g (741 millimoles) 
magnesium chips in 300 ml dodecane are heated. with stirring at the 
boiling temperature (216.degree. C.) for 1.5 hours. The H.sub.2 evolution 
resulting from the dehydration amounted to 180 millimoles. 
Thereafter, a mixture of 33.0 g (445 millimoles) tertiary butanol and 50 ml 
dodecane is added in drops within 2 hours and the mixture is then 
maintained at the boiling temperature for an additional hour. This 
resulted in an evolution of 440 millimoles H.sub.2 owing to the formation 
of cesium tertiary butylate. 
The reaction product mixture consisted of a grey suspension and contained 
cesium spheres, which has a silvery luster and had been formed by the 
reaction of the cesium tertiary butylate with the surplus magnesium metal 
(122 millimoles). When the reaction product mixture had cooled to about 
20.degree. C. it was filtered through a sieve to separate the cesium 
metal. Yield: 11.7 g (88 millimoles)=36% of theoretical yield. The 
filtrate that had passed through the sieve was filtered through a frit. 
The residue retained on the frit was washed several times with 
tetrahydrofurane. 
From the frit filtrate containing 276 millimoles cesium butylate and 84 
millimoles magnesium butylate, pure cesium butylate could be recovered by 
recrystallization from a mixture of tetrahydrofurane and toluene.