Processes and reactors for alkali metal production

Abstract

Electrochemical processes and apparatus for obtaining metals from metal salts, including for separating alkali metal and alcohols from alkali metal alkoxide compounds, are disclosed. Aqueous solutions of metal alkoxides or metal carbonates are converted to metals by electrochemical processes which may also be integrated into processes for the production of borohydrides, such as sodium borohydride.

1 . An electrochemical cell comprising:
 an anode compartment containing an anode, the anode compartment having a first inlet and a first outlet;   a cathode compartment containing a, cathode, the cathode compartment having a second inlet and a second outlet; and   a separator located between the anode and cathode compartments, wherein the separator is permeable to ions, and wherein the separator is held in a polymer frame that is substantially impervious to water.   
   
   
       2 . The electrochemical cell of  claim 1 , wherein the polymer is selected from the group consisting of polyphenylene sulfide and polyetheretherketone. 
   
   
       3 . The electrochemical cell of  claim 1 , wherein the separator comprises a material selected from the group consisting of lithium-β-aluminum oxide, lithium-β″-aluminum oxide, lithium-β/β″-aluminum oxide, sodium-β-aluminum oxide, sodium-β″-aluminum oxide, sodium-β/β″-aluminum oxide, potassium-β-aluminum oxide, potassium-β″-aluminum oxide and potassium-β/β″-aluminum oxide. 
   
   
       4 . The electrochemical cell of  claim 1 , wherein the separator is a NaSICON, a LiSICON or a KSICON membrane. 
   
   
       5 . The electrochemical cell of  claim 1 , wherein the separator is round. 
   
   
       6 . A reactor comprising:
 a first compartment containing a first electrode;   a second compartment;   a first separator located between the first and second compartments, wherein the separator is permeable to ions;   a third compartment containing a second electrode; and   a second separator located between the second and third compartments, wherein the separator is permeable to ions.   
   
   
       7 . The reactor of  claim 6 , further comprising a gas inlet in the first compartment. 
   
   
       8 . The reactor of  claim 6 , wherein the reactor is configured to maintain the third compartment at a temperature of about 5° C. to about 110° C. 
   
   
       9 . The reactor of  claim 6 , wherein at least one of the first and second separators comprises a material selected from the group consisting of lithium-β-aluminum oxide, lithium-β″-aluminum oxide, lithium-β/β″-aluminum oxide, sodium-β-aluminum oxide, sodium-β″-aluminum oxide, sodium-β/β″-aluminum oxide, potassium-β-aluminum oxide, potassium-β″-aluminum oxide and potassium-β/β″-aluminum oxide. 
   
   
       10 . The reactor of  claim 6 , wherein at least one of the first and second separators is a NaSICON, a LiSICON or KSICON membrane. 
   
   
       11 . A process for reducing a metal salt of formula M n OR wherein M is a metal cation selected from the group consisting of Li + , Na + , K + , Rb + , Cs + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+  and Ba 2+ ; R is selected from the group consisting of H and straight- or branched-chain or cyclic alkyl groups containing from 1 to 6; and n is the valence of the active metal cation compound, comprising:
 providing an electrolytic cell containing anode and cathode compartments separated by a separator which is permeable to ions;   supplying at least one metal salt to the anode compartment;   applying an electric potential to the cell; and   providing hydrogen to the anode compartment.   
   
   
       12 . The process of  claim 11 , wherein the electrical potential is from about 1 volt to about 7 volts. 
   
   
       13 . The process of  claim 11 , further comprising electrooxidizing hydrogen at the anode. 
   
   
       14 . The process of  claim 11 , further comprising maintaining the cathode compartment at a temperature of about 95° C. to about 150° C. 
   
   
       15 . A process for reducing a metal carbonate, comprising:
 providing a reactor comprising a first compartment containing a first electrode, a second compartment, a first separator between the first and second compartments, a third compartment containing a second electrode, and a second separator between the second and third compartments, wherein the first and second separators are permeable to ions;   supplying a metal carbonate compound to the first compartment;   supplying a metal alkoxide salt to the second compartment; and   applying an electric potential to the cell.   
   
   
       16 . The process of  claim 15 , wherein the electrical potential is from about 1 volt to about 15 volts. 
   
   
       17 . The process of  claim 16 , wherein the electrical potential is from about 2 volts to about 10 volts. 
   
   
       18 . The process of  claim 17 , wherein the electrical potential is from about 3 volts to about 3.5 volts. 
   
   
       19 . The process of  claim 15 , further comprising supplying hydrogen to the first compartment and electrooxidizing hydrogen. 
   
   
       20 . A process for producing sodium borohydride, comprising:
 reacting sodium hydride and trialkylborate to produce sodium borohydride and sodium alkoxide;   separating the sodium borohydride and the sodium alkoxide by extraction with a solvent;   electrolyzing the sodium alkoxide to sodium metal and an alcohol; and   reacting the sodium metal with hydrogen to produce sodium hydride.   
   
   
       21 . The process of  claim 20 , further comprising electrolyzing sodium carbonate to produce sodium and reacting the sodium with hydrogen to form sodium hydride. 
   
   
       22 . The process of  claim 20 , further comprising:
 reacting the alcohol with boric acid to prepare a triaklyborate; and   electrolyzing a mixture comprising an alcohol and sodium borate to produce sodium and trialkylborate, and reacting the sodium with hydrogen to form sodium hydride.   
   
   
       23 . The process of  claim 20 , wherein the solvent is selected from the group consisting of an alcohol, an esther, an amine, dimethylacetamide, dimethylsulfoxide and acetonitrile. 
   
   
       24 . The process of  claim 23 , wherein the alcohol is selected from the group consisting of methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, tert-butanol, pentanol, hexanol and phenol. 
   
   
       25 . The process of  claim 23 , wherein the ether is selected from the group consisting of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and tetrahydrofuran.