Process for recovering alkali metals and sulfur from alkali metal sulfides and polysulfides

Abstract

Alkali metals and sulfur may be recovered from an oil desulfurization process which utilized alkali metal in an electrolytic process that utilizes an electrolytic cell having an alkali ion conductive membrane. An anolyte solution includes an alkali monosulfide, an alkali polysulfide, or a mixture thereof and a solvent that dissolves elemental sulfur. A catholyte includes molten alkali metal. Applying an electric current oxidizes sulfide and polysulfide in the anolyte compartment, causes alkali metal ions to pass through the alkali ion conductive membrane to the catholyte compartment, and reduces the alkali metal ions in the catholyte compartment. Liquid sulfur separates from the anolyte solution and may be recovered. The electrolytic cell is operated at a temperature where the formed alkali metal and sulfur are molten.

1 . A process for electrochemically oxidizing alkali metal monosulfides and polysulfides obtained from an oil desulfurization process comprising:
 separating one or more solids containing at least one of the alkali metal monosulfides and alkali metal polysulfides from a liquid comprising the solids;   thermally treating the solids in a nonoxidizing environment;   adding the thermally treated solids to a solvent to at least partially dissolve at least one of the alkali metal monosulfides and alkali metal polysulfides to create a plurality of alkali ions and at least one of a sulfide and a polysulfide;   obtaining an electrolytic cell comprising an alkali ion conductive membrane configured to selectively transport alkali ions, the membrane separating an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode;   introducing into the anolyte compartment an anolyte solution comprising an anolyte solvent that partially dissolves elemental sulfur, the plurality of alkali ions and at least one of a sulfide and a polysulfide;   introducing into the catholyte compartment a catholyte wherein the catholyte comprises a molten alkali metal;   applying an electric current to the electrolytic cell at an operating temperature thereby:
 i. oxidizing at least one of a sulfide and a polysulfide in the anolyte compartment to form liquid elemental sulfur; 
 ii. causing the plurality of alkali ions to pass through the alkali ion conductive membrane from the anolyte compartment to the catholyte compartment; and 
 iii. reducing the plurality of alkali ions in the catholyte compartment to form liquid elemental alkali metal; 
   allowing liquid elemental sulfur to become saturated in the anolyte solution and to form a second liquid phase.   
     
     
         2 . The process according to  claim 1  where the liquid elemental sulfur separates from the anolyte solution in a settling zone that is within the electrolytic cell. 
     
     
         3 . The process according to  claim 1  where the liquid elemental sulfur separates from the anolyte solution in a settling zone that is external to the cell. 
     
     
         4 . The process according to  claim 1  where the separation of liquid elemental sulfur from the anolyte solution includes one or more of the separation techniques selected from gravimetric, filtration, and centrifugation. 
     
     
         5 . The process according to  claim 1 , wherein the alkali ion conductive membrane is substantially impermeable to anions, the catholyte solvent, the anolyte solvent, and dissolved sulfur. 
     
     
         6 . The process according to  claim 1 , wherein the alkali ion conductive membrane comprises in part an alkali metal conductive ceramic or glass ceramic. 
     
     
         7 . The process according to  claim 1 , wherein the alkali ion conductive membrane comprises a solid MSICON (Metal Super Ion CONducting) material, where M is Na or Li. 
     
     
         8 . The process according to  claim 1 , wherein the anolyte solvent comprises one or more solvents selected from N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene, tetraethylene glycol dimethyl ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether, dimethylpropyleneurea, formamide, methyl formamide, dimethyl formamide, acetamide, methyl acetamide, dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. 
     
     
         9 . The process according to  claim 1 , wherein the anolyte solvent comprises from about 60-100 vol. % polar solvent and 0-40 vol. % apolar solvent. 
     
     
         10 . A process for electrochemically oxidizing alkali metal monosulfides and polysulfides obtained from an oil desulfurization process comprising:
 separating one or more solids containing at least one of the alkali metal monosulfides and alkali metal polysulfides from a liquid comprising the solids;   thermally treating the solids in a nonoxidizing environment;   adding the thermally treated solids to a solvent to at least partially dissolve at least one of the alkali metal monosulfides and alkali metal polysulfides to create a plurality of alkali ions and at least one of a sulfide and a polysulfide;   obtaining an electrolytic cell comprising an alkali ion conductive membrane configured to selectively transport alkali ions, the membrane separating an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode;   introducing into the anolyte compartment an anolyte solution comprising an anolyte solvent that partially dissolves elemental sulfur, the plurality of alkali ions and at least one of a sulfide and a polysulfide;   introducing into the catholyte compartment a catholyte wherein the catholyte comprises a molten alkali metal;   applying an electric current to the electrolytic cell at an operating temperature thereby:
 i. oxidizing at least one of a sulfide and a polysulfide in the anolyte compartment to form a higher level polysulfide; 
 ii. causing the plurality of alkali ions to pass through the alkali ion conductive membrane from the anolyte compartment to the catholyte compartment; and 
 iii. reducing the plurality of alkali ions in the catholyte compartment to form liquid elemental alkali metal; 
   transporting the anolyte solution from the first electrolytic cell to a second electrolytic cell comprising an alkali ion conductive membrane configured to selectively transport alkali ions, the membrane separating an anolyte compartment configured with an anode and a catholyte compartment configured with a cathode and a catholyte;   applying an electric current to the second electrolytic cell thereby:
 i. oxidizing the higher level polysulfide in the anolyte compartment to form liquid elemental sulfur; 
 ii. causing the plurality of alkali ions to pass through the alkali ion conductive membrane from the anolyte compartment to the catholyte compartment; and 
 iii. reducing the plurality of alkali ions in the catholyte compartment to form liquid elemental alkali metal; 
   allowing liquid elemental sulfur to become saturated in the anolyte solution and to form a second liquid phase.   
     
     
         11 . The process according to  claim 10  where the liquid elemental sulfur separates from the anolyte solution in a settling zone that is within the electrolytic cell. 
     
     
         12 . The process according to  claim 10  where the liquid elemental sulfur separates from the anolyte solution in a settling zone that is external to the cell. 
     
     
         13 . The process according to  claim 10  where the separation of liquid elemental sulfur from the anolyte solution includes one or more of the separation techniques selected from gravimetric, filtration, and centrifugation. 
     
     
         14 . The process according to  claim 10 , wherein the alkali ion conductive membrane is substantially impermeable to anions, the catholyte solvent, the anolyte solvent, and dissolved sulfur. 
     
     
         15 . The process according to  claim 10 , wherein the alkali ion conductive membrane comprises in part an alkali metal conductive ceramic or glass ceramic. 
     
     
         16 . The process according to  claim 10 , wherein the alkali ion conductive membrane comprises a solid MSICON (Metal Super Ion CONducting) material, where M is Na or Li. 
     
     
         17 . The process according to  claim 10 , wherein the anolyte solvent comprises one or more solvents selected from N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene, tetraethylene glycol dimethyl ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether, dimethylpropyleneurea, formamide, methyl formamide, dimethyl formamide, acetamide, methyl acetamide, dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. 
     
     
         18 . The process according to  claim 10 , wherein the anolyte solvent comprises from about 60-100 vol. % polar solvent and 0-40 vol. % apolar solvent. 
     
     
         19 . An electrolytic cell for oxidizing alkali metal polysulfides obtained from an oil desulfurization process comprising:
 an anolyte compartment configured with an anode and containing an anolyte solution comprising an alkali metal monosulfide, an alkali metal polysulfide, or a mixture thereof and an anolyte solvent that partially dissolves elemental sulfur, the anolyte compartment further comprising an anolyte solution inlet and an anolyte solution outlet;   a catholyte compartment configured with a cathode and containing a catholyte, wherein the catholyte comprises a molten alkali metal, the catholyte compartment further comprising a catholyte outlet;   an alkali ion conductive membrane configured to selectively transport alkali ions, wherein the alkali ion conductive membrane is substantially impermeable to anions, the anolyte solvent, and dissolved sulfur;   a source of electric potential electrically coupled to the anode and the cathode and configured to:
 oxidize monosulfide or polysulfide in the anolyte compartment to form liquid elemental sulfur; 
 cause alkali metal ions to pass through the alkali ion conductive membrane from the anolyte compartment to the catholyte compartment; and 
 reduce the alkali metal ions in the catholyte compartment to form liquid elemental alkali metal; and 
   an elemental sulfur settling zone where liquid elemental sulfur separates from the anolyte solution.   
     
     
         20 . The electrolytic cell according to  claim 19 , wherein the alkali ion conductive membrane comprises in part an alkali metal conductive ceramic or glass ceramic. 
     
     
         21 . The electrolytic cell according to  claim 19 , wherein the alkali ion conductive membrane comprises a solid MSICON (Metal Super Ion CONducting) material, where M is Na or Li. 
     
     
         22 . The electrolytic cell according to  claim 19 , wherein the anolyte solvent comprises one or more solvents selected from N,N-dimethylaniline, quinoline, tetrahydrofuran, 2-methyl tetrahydrofuran, benzene, cyclohexane, fluorobenzene, thrifluorobenzene, toluene, xylene, tetraethylene glycol dimethyl ether (tetraglyme), diglyme, isopropanol, ethyl propional, dimethyl carbonate, dimethoxy ether, dimethylpropyleneurea, formamide, methyl formamide, dimethyl formamide, acetamide, methyl acetamide, dimethyl acetamide, triethylamine, diethyl acetamide, ethanol and ethyl acetate, propylene carbonate, ethylene carbonate, and diethyl carbonate. 
     
     
         23 . The electrolytic cell according to  claim 19 , wherein the anolyte solvent comprises from about 60-100 vol. % polar solvent and 0-40 vol. % apolar solvent. 
     
     
         24 . The electrolytic cell according to  claim 19 , further comprising a sulfur outlet for removal of elemental sulfur from the electrolytic cell.