Process for preparing an alkali metal

Abstract

Process for preparing an alkali metal from a salt of the alkali metal which is soluble in a solvent, including a first electrolysis, a concentration, and a second electrolysis. The first electrolysis produces a product mixture. This product mixture is then concentrated to give a largely solvent-free alkali metal (poly)sulfide melt. A second electrolysis at a temperature above the melting point of the alkali metal is then performed in a second electrolysis cell comprising an anode space and a cathode space, separated by a solid electrolyte which conducts alkali metal cations. The alkali metal (poly)sulfide melt from the concentration step is fed to the anode space. Sulfur is removed from the anode space and liquid alkali metal is removed from the cathode space.

1 .- 14 . (canceled) 
     
     
         15 . A process for preparing an alkali metal from a salt of the alkali metal which is soluble in a solvent, said process comprising
 (a) carrying out a first electrolysis in a first electrolysis cell comprising an anode space and a cathode space, where the anode space and the cathode space of the first electrolysis cell are separated by a membrane which is permeable to alkali metal cations, wherein the salt of the alkali metal dissolved in a first solvent is fed to the anode space and a suspension comprising sulfur and a second solvent is fed to the cathode space, and wherein a mixture comprising the second solvent, the alkali metal cations, (poly)sulfide anions, and further ionic sulfur compounds, is taken off from the cathode space,   (b) concentrating the mixture comprising the second solvent, the alkali metal cations, the (poly)sulfide anions, and the further ionic sulfur compounds, which is taken off from the cathode space, to give a largely solvent-free alkali metal (poly)sulfide melt,   (c) carrying out a second electrolysis at a temperature above the melting point of the alkali metal in a second electrolysis cell comprising an anode space and a cathode space, where the anode space and the cathode space of the second electrolysis cell are separated by a solid electrolyte which conducts alkali metal cations, and wherein the alkali metal (poly)sulfide melt from step (b) is fed to the anode space and sulfur is taken off from the anode space and liquid alkali metal is taken off from the cathode space.   
     
     
         16 . The process of  claim 15 , wherein concentration of the alkali metal cations and the (poly)sulfide anions in the mixture comprising the second solvent, the alkali metal cations, the (poly)sulfide anions, and the further ionic sulfur compounds, which is taken off from the cathode space of the first electrolysis cell, is carried out in an evaporator. 
     
     
         17 . The process of  claim 15 , wherein the concentrating step is carried out at a temperature in the range from 80 to 400° C. and a pressure of the vapor in the range from 0.1 to 2 bar absolute. 
     
     
         18 . The process of  claim 15 , wherein the concentrated mixture obtained in step (b) is purified before carrying out the second electrolysis. 
     
     
         19 . The process of  claim 18 , wherein the concentrated mixture obtained in step (b) is brought into contact with a gaseous stream comprising hydrogen sulfide to effect purification. 
     
     
         20 . The process of  claim 19 , wherein the concentrated mixture obtained in step (b) and the gaseous stream comprising hydrogen sulfide are conveyed in counter-current. 
     
     
         21 . The process of  claim 19 , wherein the purification is carried out in a column, and wherein the concentrated mixture obtained in step (b) is fed in at the top of the column and the gaseous stream comprising hydrogen sulfide is fed in via a side inlet. 
     
     
         22 . The process of  claim 21 , wherein the column is heated below the side inlet for the gaseous stream comprising hydrogen sulfide. 
     
     
         23 . The process of  claim 15 , wherein the solid electrolyte which conducts alkali metal cations of the second electrolysis cell comprises alkali metal β-aluminum oxide, alkali metal β″-aluminum oxide or alkali metal β/β″-aluminum oxide. 
     
     
         24 . The process of  claim 15 , wherein the sulfur taken off from the anode space of the second electrolysis cell is recirculated to the first electrolysis in step (a). 
     
     
         25 . The process of  claim 15 , wherein the alkali metal is sodium, potassium, or lithium. 
     
     
         26 . The process of  claim 15 , wherein the salt of the alkali metal is an alkali metal halide. 
     
     
         27 . The process of  claim 15 , wherein the salt of the alkali metal is sodium chloride. 
     
     
         28 . The process of  claim 15 , wherein the first solvent and/or the second solvent is water.