Electrochemical separation and concentration of sulfur containing gases from gas mixtures

Abstract

A method of removing sulfur oxides of H 2 S from high temperature gas mixtures (150°-1000° C.) is the subject of the present invention. An electrochemical cell is employed. The cell is provided with inert electrodes and an electrolyte which will provide anions compatible with the sulfur containing anions formed at the anode. The electrolyte is also selected to provide inert stable cations at the temperatures encountered. The gas mixture is passed by the cathode where the sulfur gases are converted to SO 4 ═ or, in the case of H 2 S, to S═. The anions migrate to the anode where they are converted to a stable gaseous form at much greater concentration levels (>10X). Current flow may be effected by utilizing an external source of electrical energy or by passing a reducing gas such as hydrogen past the anode.

I claim: 
     
       1. A method of removing .[.sulfur gases.]. .Iadd.SO 2  .Iaddend.from a gas mixture at a temperature of about 150° C. or above, said method comprising the steps of: providing an electrochemical cell having an inert .Iadd.gas porous .Iaddend.cathode and an inert anode.Iadd., said cathode and anode being held in place in said cell by porous members.Iaddend.;   providing said cell with an electrolyte which is molten at temperatures above about 150° C. selected from the group comprising alkali metal sulfates, alkali metal bisulfates, and alkali metal pyrosulfates;   raising the temperature of said cell to at least 150° C. whereby said electrolyte is in its molten state;   .[.effecting.]. .Iadd.providing an external source of electrical energy to effect .Iaddend.current flow between said cathode and said anode;   directing said gas mixture past said cathode where oxidation of .[.sulfur.]. .Iadd.SO 2  .Iaddend.occurs and sulfur containing anions are formed which migrate .[.toward.]. .Iadd.from said cathode to .Iaddend.said anode .[.and are converted.]. .Iadd.converting said sulfur containing anions to SO 3  at said anode .Iaddend..[.to gaseous species.]. .Iadd.SO 3  .Iaddend.,   whereby concentrated .[.sulfur gases are.]. .Iadd.SO 3  is .Iaddend.evolved at said anode.   
     
     
       2. A method as set forth in claim 1, .[.wherein said sulfur gases comprise principally SO 2  and.]. wherein said step of directing said gas mixture past said cathode results in the formation of SO 4   --  ions at the cathode. .[.3. A method as set forth in claim 2, wherein said step of providing an electrolyte comprises providing at least one alkali metal salt..]. .[.4. A method as set forth in claim 2, wherein said step of providing an electrolyte comprises selecting at least one alkali metal salt from the group consisting of SO 4   -- , HSO 4   -  and S 2  O 7   -- ..]. .[.5. A method as set forth in claim 1, wherein said step of effecting current flow comprises providing an external source of electrical energy across said anode and cathode..]. .[.6. A method as set forth in claim 1, wherein said step of effecting current flow comprises passing a reducing gas past said anode..]. .[.7. A method as set forth in claim 6, wherein said step of passing a reducing gas comprises passing hydrogen past said anode..]. .[.8. A method as set forth in claim 1, wherein said sulfur gases comprise principally H 2  S and wherein said step of directing said gas mixture past said cathode results in the formation of S --  ions..]. .[.9. A method as set forth in claim 8, wherein said step of providing an electrolyte comprises providing at least one alkali metal salt..]. .[.10. A method as set forth in claim 8, wherein said step of providing an electrolyte comprises providing at least one 
     
     
        alkali metal sulfide salt..]. .[.11.  A method as set forth in claim 8, wherein said step of effecting current flow comprises providing an external source of electrical energy across said anode and cathode..]. .[.12. A method as set forth in claim 8, wherein said step of effecting current flow comprises passing a reducing gas past said anode..]. .[.13. A method as set forth in claim 12, wherein said step of passing a reducing 
     
     
        gas comprises passing hydrogen past said anode..]. 14. A method of removing .[.sulfur gases.]. .Iadd.SO 2  .Iaddend.from a gas mixture at a temperature of about 150° C. or above, utilizing an electrochemical cell characterized by an inert anode and an inert .[.cathode.]. .Iadd.gas porous cathode held in place in said cell by porous members .Iaddend.and having an electrolyte which is molten at operating temperatures, said electrolyte being selected from the group comprising alkali metal sulfates, alkali metal bisulfates and alkali metal pyrosulfates, said method comprising the steps of: raising the temperature of said cell to at least 150° C. whereby said electrolyte is in its molten state;   .[.effecting.]. .Iadd.providing an external source of electrical energy to effect .Iaddend.current flow betwee said cathode and said anode;   directing said gas mixture past said cathode where oxidation of .[.sulfur.]. .Iadd.SO 2  .Iaddend.occurs and sulfur containing anions are formed which migrate .[.toward.]. .Iadd.from said cathode to .Iaddend.said anode .[.and.]. .Iadd.where they .Iaddend.are converted to .[.gaseous species.]. .Iadd.SO 3  .Iaddend.,   whereby concentrated .[.sulfur gases are.]. .Iadd.SO 3  is   
     
     
        .Iaddend.evolved at said anode. 15. A method as set forth in claim 14, wherein is included the step of recovering said gas evolving at said anode. .[.16. A method as set forth in claim 15, wherein said step of effecting current flow, comprises providing an external source of electrical energy across said anode and cathode..]. .[.17. A method as set forth in claim 15, wherein said step of effecting current flow comprises 
     
     
        passing a reducing gas past said anode..]. 18. A method as set forth in claim 14, .[.wherein said sulfur gases comprise principally SO 2  and.]. wherein said step of directing said gas mixture past said cathode results in the formation of SO 4   --  ions at said cathode. .[.19. A method as set forth in claim 14, wherein said sulfur gases comprise principally H 2  S and wherein said step of directing said gas mixture past said cathode results in the formation of S --  ions at said cathode..].