Anode useful for electrochemical conversion of anhydrous hydrogen halide to halogen gas

Abstract

A particular anode comprising an electrochemically active material selected from the group .[.comprising.]. .Iadd.consisting of .Iaddend.the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of such elements is useful in an electrochemical cell for the direct production of essentially dry halogen gas from essentially anhydrous halogen halide, or in a process for such production of essentially dry halogen gas. This cell or process may be used to produce halogen gas such as chlorine, bromine, fluorine and iodine from a respective anhydrous hydrogen halide, such as hydrogen chloride, hydrogen bromide, hydrogen fluoride and hydrogen iodide.

What is claimed is: 
     
       1. A process for the direct production of essentially dry halogen gas from essentially anhydrous hydrogen halide, wherein molecules of essentially anhydrous hydrogen halide are fed to an inlet of an electrochemical cell comprising a cation-transporting membrane, a cathode disposed in contact with one side of the membrane and an anode disposed in contact with the other side of the membrane and are transported to the anode of the cell, the anode and the cathode each comprising an electrochemically active material, wherein the electrochemically active material of the anode is selected from the group consisting of the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of said elements, and further wherein the molecules of the essentially anhydrous hydrogen halide are oxidized at the anode to produce essentially dry halogen gas and protons, the protons are transported through the membrane and the transported protons are reduced at the cathode. 
     
     
       2. The process of claim 1, wherein the hydrogen halide is selected from the group consisting of: hydrogen chloride, hydrogen bromide, hydrogen fluoride and hydrogen iodide. 
     
     
       3. The process of claim 1, wherein the transported protons are reduced to form hydrogen gas. 
     
     
       4. The process of claim 1, further including the step of keeping the cathode side of the membrane moist to increase the efficiency of proton transport through the membrane. 
     
     
       5. An electrochemical cell for the direct production of essentially dry halogen gas from essentially anhydrous hydrogen halide, comprising: (a) means for oxidizing molecules of essentially anhydrous hydrogen halide to produce essentially dry halogen gas and protons, the oxidizing means comprising an electrochemically active material, wherein the electrochemically active material is selected from the group consisting of the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of said elements;   (b) cation-transporting means for transporting the protons therethrough, wherein the oxidizing means is disposed in contact with one side of the cation-transporting means; and   (c) means for reducing the transported protons, wherein the reducing means is disposed in contact with the other side of the cation-transporting means.   
     
     
       6. The electrochemical cell of claim 5, wherein the electrochemically active material comprises tin oxide. 
     
     
       7. The electrochemical cell of claim 5, wherein the oxidizing means is an anode and the reducing means is a cathode, and further wherein the anode and the cathode are gas-diffusion electrodes. 
     
     
       8. The electrochemical cell of claim 7, wherein the cathode also comprises an electrochemically active material. 
     
     
       9. The electrochemical cell of claim 8, wherein the electrochemically active material of the cathode comprises one of the following elements: platinum, ruthenium, osmium, rhenium, rhodium, iridium, palladium, gold, titanium and zirconium, the oxides of said elements, the alloys of said elements and mixtures comprising any of said elements, oxides and alloys. 
     
     
       10. The electrochemical cell of claim 7, wherein the anode comprises tin oxide extended with carbon. 
     
     
       11. The electrochemical cell of claim 10, wherein the cathode comprises ruthenium oxide extended with carbon. 
     
     
       12. A process for the direct production of essentially dry halogen gas from essentially anhydrous hydrogen halide, wherein: (a) molecules of essentially anhydrous hydrogen halide are fed to an inlet of an electrochemical cell and are transported to an anode of the cell, the anode comprising an electrochemically active material, wherein the electrochemically active material is selected from the group consisting of the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of said elements;   (b) the molecules of the essentially anhydrous hydrogen halide are oxidized at the anode to produce essentially dry halogen gas and protons;   (c) the protons are transported through a cation-transporting membrane of the electrochemical cell to a cathode, the membrane having an anode side and a cathode side;   (d) a gas containing oxygen is introduced at the cathode side of the membrane; and   (e) the transported protons are reduced at the cathode, and the protons and oxygen are reduced at the cathode to form water.   
     
     
       13. The process of claim 12, wherein the oxygen-containing gas comprises one of the following air, oxygen and oxygen-enriched air. 
     
     
       14. A process for recycling unreacted anhydrous hydrogen halide generated from the direct production of essentially dry halogen gas from essentially anhydrous hydrogen halide, wherein: (a) molecules of essentially anhydrous hydrogen halide are fed to an inlet of an electrochemical cell and are transported to an anode of the cell, wherein the anode comprises an electrochemically active material selected from the group consisting of the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of said elements;   (b) a portion of the essentially anhydrous hydrogen halide is oxidized at the anode to produce essentially dry halogen gas and protons;   (c) the protons are transported through a cation-transporting membrane of the electrochemical cell;   (d) the transported protons are reduced at a cathode of the electrochemical cell;   (e) another portion of the essentially anhydrous hydrogen halide is unreacted and is separated from the essentially dry halogen gas; and   (f) the unreacted, separated portion of the anhydrous hydrogen halide exits the cell through an outlet thereof and is recycled to the inlet of the electrochemical cell.   
     
     
       15. The process of claim 14, wherein the essentially dry halogen gas is recycled to a synthesis process which produces anhydrous hydrogen halide as a by-product. 
     
     
       16. A process for recycling essentially dry halogen gas to a synthesis process, wherein the essentially dry halogen gas is generated directly from essentially anhydrous hydrogen halide, wherein: (a) molecules of essentially anhydrous hydrogen halide are fed to an inlet of an electrochemical cell and are transported to an anode of the cell, wherein the anode comprises an electrochemically active material selected from the group consisting of the oxides of the elements tin, germanium and lead and mixtures comprising at least one of the respective oxides of said elements;   (b) a portion of the essentially anhydrous hydrogen halide is oxidized at the anode to produce essentially dry halogen gas and protons;   (c) the protons are transported through a cation-transporting membrane of the electrochemical cell;   (d) the transported protons are reduced at a cathode of the electrochemical cell; and   (e) the essentially dry halogen gas is recycled to a synthesis process which produces anhydrous hydrogen halide as a by-product.