Hydrogen production in the process of electrochemical treatment of sulfur-containing acid gases (hydrogen sulfide or sulfur dioxide) supplied in solution with amine-based or other organic absorbents

Abstract

A method and an electrochemical cell for hydrogen production by electrochemical decomposition of a sulfur-containing acid gas such as H.sub.2S or SO.sub.2 are disclosed. The method comprises electrolysis of the acid gas in solution in the presence of an absorbent, which may be chemical, physical, or a mixture thereof. In typical embodiments, the absorbent is alkanolamine-based.

Claims

1. A method for production of hydrogen gas in the presence of a sulfur-containing acid gas, said method comprising: providing at least one electrochemical cell, said electrochemical cell comprising: at least one positive electrode (anode) and one negative electrode (cathode); solution supply and withdrawal means for supplying and withdrawing a feed/electrolyte solution to and from said electrochemical cell; product withdrawal means for withdrawing from said electrochemical cell products of electrochemical reactions occurring within said electrochemical cell; and, electrical connecting means configured to provide external electrical connections to at least one of said positive electrode and said negative electrode; supplying to said electrochemical cell a feed/electrolyte solution comprising a sulfur-containing acid gas and at least one absorbent for said sulfur-containing acid gas; connecting said electrochemical cell to an external power supply so as to cause within said electrochemical cell an electrochemical reaction that produces hydrogen gas; and, removing said electrochemically produced hydrogen gas from said electrochemical cell; wherein: said feed/electrolyte solution is selected from the group consisting of: feed/electrolyte solutions comprising hydrogen sulfide and a hydrogen sulfide absorbent comprising an alkanolamine; feed/electrolyte solutions comprising hydrogen sulfide and a physical hydrogen sulfide absorbent selected from the group consisting of N-methylpyrrolidone, dimethyl ether of polyethylene glycol, tributyl phosphate, and methanol; and, feed/electrolyte solutions comprising sulfur dioxide, water, and a sulfur dioxide absorbent selected from the group consisting of primary amines, secondary amines, tertiary amines, triamines, and tetraamines.

2. The method according to claim 1, wherein said step of supplying a feed/electrolyte solution comprising a sulfur-containing acid gas and at least one absorbent for said sulfur-containing gas comprises supplying a feed/electrolyte solution comprising at least 10% by weight of said absorbent.

3. The method according to claim 1, wherein: said electrochemical cell comprises a proton-conductive separator that divides said cell into an anode compartment in electrical connection with said anode and a cathode compartment in electrical connection with said cathode; and, said solution supply and withdrawal means are in fluid connection with said anode compartment but are not in fluid connection with said cathode compartment.

4. The method according to claim 3, wherein said proton-conductive separator comprises at least one component selected from the group consisting of proton-conductive membranes and catalyst layers.

5. The method according to claim 4, wherein: said proton-conductive separator comprises a catalyst layer, said catalyst layer comprising an anode side and a cathode side; said anode side comprises a catalyst selected from the group consisting of platinum, ruthenium, palladium, and mixtures thereof; and, said cathode side comprises a catalyst selected from the group consisting of platinum, ruthenium, palladium, iridium, aluminum, lead, metal oxides, mixtures thereof, alloys thereof, and combinations thereof.

6. The method according to claim 1, wherein said feed/electrolyte solution comprises hydrogen sulfide and a hydrogen sulfide absorbent and said method comprises removing from said electrochemical cell sulfur produced in said electrochemical reaction.

7. The method according to claim 1, wherein: said feed/electrolyte solution comprises hydrogen sulfide and an absorbent comprising an alkanolamine; and, said alkanolamine is selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine, and mixtures thereof.

8. The method according to claim 1, wherein said feed/electrolyte solution comprises sulfur dioxide, water, and a sulfur dioxide absorbent and, said method comprises removing from said electrochemical cell said feed/electrolyte solution containing products of said electrochemical reaction.

9. The method according to claim 4, wherein said proton-conductive separator comprises at least one of: an anode side catalyst layer comprising a catalyst selected from the group consisting of platinum, ruthenium, palladium, and mixtures thereof; and, a cathode side catalyst layer comprising a catalyst selected from the group consisting of platinum, ruthenium, palladium, iridium, aluminum, lead, metal oxides, mixtures thereof, alloys thereof, and combinations thereof.

10. The method according to claim 1, wherein: said feed/electrolyte solution comprises sulfur dioxide and a sulfur dioxide absorbent, and, said sulfur dioxide absorbent is selected from the group consisting of: at least one amine compound selected from the group consisting of Monoethanolamine (MEA), Diethanolamine (DEA), Trimethylamine (TMA), Triethylamine (TEA), Triethanolamine (TEOA), Methyldiethanolamine (MDEA), Dimethylamine (DMA), Diisopropanolamine (DIPA), Diglycolamine (DGA), Tripropanolamine, Tributanolamine, Tetrahydroxy-methylenediamine, Tetrahydroxyethyl-ethylenediamine, Tetrahydroxyethyl-I, 3-propylenediamine, Tetrahydroxyethyl-1, 2 propylenediamine, Tetrahydroxyethyl-1, 5 -pentylenediamine, Dihydroxyethyl-ethylenediamine, Monohydroxymethyl-diethylenetriamine, Monomethyl-monohydroxylethyl-triethylenetetramine, Diethylenetriamine, Triethylenetetramine, Tetraethylenepentamine, N,N,N′,N′-Tetrakis-(2-hydroxyethyl)-I, 3-diaminopropane, N,N,N′,N′-Tetrakis-(2-hydroxyethyl)-ethylenediamine, N,N,N′,N′-Tetrakis (Z-hydroxyethyl)-ethylenediamine, N,N,N′,N′-Tetramethyl-ethylenediamine, N,N,N′,N′-Tetramethyl-diaminomethane, N,N′,N′-Trimethyl-N-(2-hydroxyethyl)-ethylenediamine, N′,N′-Dimethyl-N,N-bis(2-hydroxyethyl)-ethylenediamine, N,N′-Dimethylpiperazine, N,N′-Bis(2-hydroxyethyl)-piperazine, N-Methyl, N′-(2-hydroxyethyl)-piperazine, N-(2-hydroxyethyl)-ethylenediamine, N-(2-hydroxyethyl)-piperazine, N-Methyl-piperazine, and mixtures thereof and, at least one physical sulfur dioxide absorbent selected from the group consisting of Dimethyl ether (DME), Polyethylene glycol, Tributyl phosphate, Methanol, Dimethyl Ether of Polyethylene Glycol (DEPG), Diethylene Glycol Methyl Ether (DGM), Sulfolane (SUF), Ethylene glycol (EG), Propylene carbonate (PC), N-methylimidazole (NMI), N-Methyl-Pyrrolidone (NMP), and mixtures thereof.

11. The method according to claim 1, wherein said feed/electrolyte solution comprises sulfur dioxide, a sulfur dioxide absorbent, and at least one organic solvent selected from the group consisting of pyridine and piperazine.

12. The method according to claim 1, wherein said step of supplying to said electrochemical cell a feed/electrolyte solution comprising a sulfur-containing acid gas and at least one absorbent for said sulfur-containing acid gas comprises supplying a feed/electrolyte solution comprising a sulfur-containing acid gas obtained from sour gas.

13. The method according to claim 1, wherein said step of providing at least one electrochemical cell comprises providing a plurality of electrochemical cells connected in series.

14. An electrochemical cell (electrolyzer) for production of hydrogen in the presence of a sulfur-containing acid gas, comprising: at least one positive electrode (anode) and one negative electrode (cathode); a feed/electrolyte solution comprising said sulfur-containing acid gas; solution supply and withdrawal means for supplying and withdrawing said feed/electrolyte solution to and from said electrochemical cell; optionally, circulating means configured to circulate feed/electrolyte solution through said electrochemical cell; product withdrawal means for withdrawing from said electrochemical cell products of electrochemical reactions occurring within said electrochemical cell; and, electrical connecting means configured to provide external electrical connections to at least one of said positive electrode and said negative electrode; wherein: said feed/electrolyte solution is selected from the group consisting of: feed/electrolyte solutions comprising hydrogen sulfide and an absorbent comprising an alkanolamine; feed/electrolyte solutions comprising hydrogen sulfide and a physical hydrogen sulfide absorbent selected from the group consisting of N-methylpyrrolidone, dimethyl ether of polyethylene glycol, tributyl phosphate, and methanol; and, feed/electrolyte solutions comprising sulfur dioxide, water, and a sulfur dioxide absorbent selected from the group consisting of primary amines, secondary amines, tertiary amines, triamines, and tetraamines.

15. The electrochemical cell according to claim 14, wherein: said electrochemical cell comprises a proton-conductive separator that divides said cell into an anode compartment in electrical connection with said anode and a cathode compartment in electrical connection with said cathode; and, said solution supply and withdrawal means are in fluid connection with said anode.

16. The electrochemical cell according to claim 15, wherein said proton-conductive separator comprises at least one component selected from the group consisting of proton-conductive membranes and catalyst layers.

17. The electrochemical cell according to claim 16, wherein: said proton-conductive separator comprises a catalyst layer comprising an anode side and a cathode side; said anode side comprises a catalyst selected from the group consisting of platinum, ruthenium, palladium, and mixtures thereof; and, said cathode side comprises a catalyst selected from the group consisting of platinum, ruthenium, palladium, iridium, aluminum, lead, metal oxides, mixtures thereof, alloys thereof, and combinations thereof.

18. The electrochemical cell according to claim 14, wherein: said feed/electrolyte solution comprises hydrogen sulfide and an absorbent comprising an alkanolamine; and, said product withdrawal means comprise means for withdrawing sulfur from said electrochemical cell.

19. The electrochemical cell according to claim 14, wherein: said feed/electrolyte solution comprises sulfur dioxide, water, and a sulfur dioxide absorbent selected from the group consisting of primary amines, secondary amines, tertiary amines, triamines, and tetraamines; and, said product withdrawal means comprise means for withdrawing said feed/electrolyte solution containing products of said electrochemical reaction.

20. The electrochemical cell according to claim 14, wherein at least one of solution supply and withdrawal means and said product withdrawal means is in fluid connection with regenerating means for regenerating said absorbent from products of said electrochemical reactions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be further explained in more detail with reference to drawings, wherein:

(2) FIG. 1 shows a simplified schematic diagram of one embodiment of an apparatus for electrochemical production of hydrogen from the hydrogen sulfide supplied in solution with absorbent, comprising an electrochemical cell (electrolyzer) with a proton conductive membrane separating the electrodes; and,

(3) FIG. 2 shows a simplified schematic diagram of one embodiment of an apparatus for electrochemical production of hydrogen from water with presence of sulfur dioxide as an anode depolarizer, where the sulfur dioxide supplied in the solution with absorbent.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) The following description of certain exemplary embodiments of the invention is given to explain the principles of the invention and its practical applicability in order that a person of ordinary skill will be able to make and use the invention. The embodiments disclosed in the following description are not intended to be limiting. The invention disclosed herein is thus not defined by the particular embodiments described in the specification, but by the claims, and only by the broadest interpretation of said claims. In addition, while in some cases, for clarity, individual components, method steps, or specific combinations thereof, are described, all combinations of components or method steps disclosed in the specification that are not self-contradictory are considered by the inventor to be within the scope of the invention.

(5) With reference to electrical connections to an electrochemical cell, as used herein, the term “electrical connections from an external power supply” refers to any connection that places at least part of the electrochemical cell in electrical contact with a physical body or a circuit that is located partially or entirely outside of the electrochemical cell.

(6) As used herein, with respect to an electrochemical cell, the term “positive electrode” refers to the anode and the term “negative electrode” refers to the cathode.

(7) As used herein, with reference to electrochemical production of hydrogen from a solution containing hydrogen sulfide, the term “sulfur” is used to refer generically to any sulfur-containing species produced at the anode. Non-limiting examples of substances that fall within this definition include elemental sulfur as isolated sulfur atoms, elemental sulfur in any of its allotropic forms, and polysulfide anions.

(8) As used herein, the term “sour gas” is used to refer to a gas that contains at least one acidic sulfur gas such as H.sub.2S or SO.sub.2 as an impurity.

(9) The invention disclosed herein provides a method and system for electrochemical production of hydrogen in the presence of a sulfur-containing acid as, and for electrochemical purification of a gas that comprises a sulfur-containing acid gas. In preferred embodiments of the invention, the sulfur-containing acid gas is H.sub.2S or SO.sub.2.

(10) In the case where the gas contains hydrogen sulfide, the reaction is carried out in an electrochemical cell (electrolyzer) where hydrogen sulfide is decomposed electrochemically to hydrogen gas and elemental sulfur. The regeneration of hydrogen sulfide rich absorbents in an electrochemical cell is likely to be more effective than traditional methods of regenerating absorbents in desorber columns by heating and reducing pressure.

(11) In preferred embodiments, alkanolamines are used as absorbents for H.sub.2S. These compounds tend to be more effective for the electrochemical decomposition of hydrogen sulfide than physical absorbents due to their use in the form of aqueous solutions.

(12) Without being bound by theory, in solution, H.sub.2S, which is acidic, reacts almost instantaneously with the basic amines by proton transfer. The amine accepts a hydrogen ion (H.sup.+) from the H.sub.2S, creating an HS.sup.− anion, eqs (22) and (23):
H.sub.2S HS.sup.−+H.sup.+  (22)
H.sub.2S+Amine⇔[Amine]H.sup.++HS.sup.−  (23)

(13) The reaction with the amine creates an anion from the acid gas, thereby removing it from the gas phase, while the amine is bound to the H.sup.+ and does not readily release it. The ionization reaction is instantaneous but can be readily reversed just by a shift in pH. When the H.sub.2S/amine feed/electrolyte solution is placed in an electrochemical cell which is then connected to an external power source, hydrogen gas will be generated at the cathode and elemental sulfur will be generated at the anode, eqs (24)-(26).
At anode: H.sub.2S.fwdarw.S+2H.sup.++2ē  (24)
At cathode: 2H.sup.++2ē.fwdarw.H.sub.2  (25)
Overall reaction: H.sub.2S.fwdarw.H.sub.2+S  (26)

(14) Different designs of electrolyzers for the electrochemical decomposition of hydrogen sulfide are within the scope of the invention. Non-limiting examples include liquid electrolyte electrolyzers and Proton Exchange Membrane (PEM) electrolyzers that have been developed for water electrolysis applications. A membrane electrode assembly (MEA) of the PEM electrolyzer provides both the reaction interface and the ion migration route; in addition, it provides a good surface for electron dispersal away from the reaction interface. The PEM electrolyzer includes a membrane that will let hydrogen ions (protons) pass through but stop hydrogen gas from flowing through. The membrane is also intended to prevent other chemical species from migrating between electrodes and undergoing undesired reactions that could poison the cathode or reduce overall process efficiency.

(15) It is within the scope of the invention to disclose an electrochemical cell configured to produce hydrogen from a gas containing an acidic sulfur-containing gas such as H.sub.2S or SO.sub.2.

(16) In the method disclosed herein, a feed/electrolyte solution comprising an acidic sulfur-containing gas and an absorbent is introduced into an electrochemical cell. The electrochemical cell is attached to an external energy source, thereby causing an electrochemical reaction to take place within the cell that generates hydrogen gas and oxidizes the sulfur in the sulfur-containing acid gas (e.g. to sulfur in the case of H.sub.2S and to H.sub.xSO.sub.y.sup.n− in the case of SO.sub.2).

(17) The feed/electrolyte solution may be prepared by any method known in the art. The feed/electrolyte solution may be prepared, for example, directly from a source of the sulfur-containing acid gas, the absorbent, and an appropriate solvent. In cases in which the sulfur-containing acid gas serves as an anode depolarizer in the electrochemical cell (e.g. when it is SO.sub.x), then the solution will necessarily contain water, as in these cases the water is the source of the electrochemically produced hydrogen gas. In some embodiments of the invention, the sulfur-containing acid gas is obtained from sour gas. While any means known in the art can be used to separate the sulfur-containing acid gas from the sour gas, in preferred embodiments of the invention, a sour gas stream is passed through a column containing a solution of an absorbent under appropriate conditions of temperature and pressure. The sulfur-containing acid gas preferentially reacts with the absorbent and is thereby at least partially removed from the sour gas stream. A purified gas stream exits the column, and the remaining solution, comprising the sulfur-containing acid gas and the absorbent, is removed from the column and used as the feed/electrolyte solution. The method and system disclosed herein can thus be integrated into a system for removing sulfur-containing impurities from sour gas, e.g. in a sour gas or flue gas scrubber.

(18) The electrochemical cell comprises at least two electrodes connected to an external power supply; in different electrochemical cell designs the electrodes can be separated by the feed/electrolyte solution or by a proton conductive separator such as a proton-conductive membrane. It is also necessary to ensure supply of the feed/electrolyte solution to the electrochemical cell and withdrawal of the regenerated solution and products of the electrochemical reaction from the cell.

(19) In those embodiments in which the acidic sulfur-containing gas is H.sub.2S, a feed/electrolyte solution comprising hydrogen sulfide and an absorbent such as an alkanolamine, a physical hydrogen sulfide absorbent, or a mixture thereof is introduced into the electrochemical cell.

(20) Reference is now made to FIG. 1, which illustrates schematically one non-limiting embodiment of an electrochemical cell for production of hydrogen from hydrogen sulfide according to the present invention. The electrochemical cell depicted in the figure comprises a frame (1); a proton exchange membrane (PEM) (2); a positive electrode (anode) (3); and a negative electrode (cathode) (4). Each electrode typically consists of an electrically-conductive structure and when the cell is in use, both are connected to an external power supply. In the embodiment shown, one PEM membrane is used; in other embodiments, a plurality of membranes may be used, or the anode and cathode can be separated by the feed/electrolyte solution. The PEM membrane can be made from polymeric, ceramic or other specially elaborated and composite materials, such as Nafion, Polybenzimidazole, Sulfornated Polybenzimidazole (s-PBI), Sulfonated Diels-Alder Polyphenylene, Sulfonated PFCB-BPVE Tetramer, Silica, Hybrid Silica Nafion nanocomposites etc., which let hydrogen ions (protons) pass through membrane but stop hydrogen gas and other compounds. PEM 2 divides the interior of frame 1 into an anode chamber (1-1) and a cathode chamber (1-1). Anode chamber 1-1 includes an inlet (5) and an outlet (6), and cathode chamber 1-2 includes an outlet (7). In operating mode, inlet 5 is used to admit into anode chamber 1-1 a feed/electrolyte solution comprising hydrogen sulfide and absorbent, and outlet 6 is used to remove the absorbent solution and the sulfur (i.e. the product of the electrochemical reaction) from the anode chamber. Molecular hydrogen generated at the cathode exits the cathode chamber via outlet 7. Note that in embodiments of the invention in which the cathode an anode are separated by the feed/electrolyte solution, there will not be separate anode and cathode chambers, and inlet 5 and outlets 6 and 7 will all be connected to the single chamber of the cell.

(21) In some embodiments of the invention in which the electrochemical cell comprises a proton-conductive separator, the separator (e.g. a PEM) comprises at least one catalyst layer that incorporates a catalyst. Such membranes and catalysts are well-known in the art, for example, in the SDE process described above. These catalysts can influence the cell voltage for the electrolysis, thereby enhancing the efficiency of the process, and can also favorably affect the stable operation of the cell. The separator may include more than one catalyst layer, and the anode and cathode sides of the separator may incorporate different catalysts. In some non-limiting preferred embodiments, the separator comprises an anode-side catalyst selected from the group consisting of platinum, ruthenium, palladium, and mixtures, alloys, and combinations thereof. In some non-limiting preferred embodiments, the separator comprises a cathode-side catalyst selected from the group consisting of platinum, ruthenium, palladium, iridium, aluminum, lead, metal oxides, and mixtures, combinations, and alloys thereof. In some preferred embodiments of the invention, the metal oxide is selected from the group consisting of oxides of palladium, ruthenium iridium, aluminum, and lead, SnO.sub.2, SbO.sub.2, TaO.sub.2, TiO.sub.2, and Ti.sub.4O.sub.7.

(22) In some embodiments of the invention, it comprises means for circulating feed/electrolyte solution through the cell. Any means known in the art (e.g. a pump with a speed and capacity appropriate for the cell) may be used. In some embodiments of the invention, the circulation means provide a fluid connection between inlet 5 and outlet 6 so that the feed/electrolyte solution is recirculated through the cell. In some embodiments of the invention, it comprises a water supply inlet to the cathode chamber. The water serves for hydration of the PEM in cases in which a physical hydrogen sulfide absorbent is used. The hydrated regions in some types of polymer electrolyte membranes create better conductivity of H.sup.+ ions. In some embodiments, the water is used for cooling or temperature control. For simplicity and clarity, certain standard elements of PEM electrochemical cell are not shown or described herein (for example anode and cathode collectors, diffusion layers and catalysts which are used in order to increase the cell's capacity).

(23) Absorbents, which are supplied to the electrochemical cell according to the invention, are preferably based on alkanolamines, non-limiting examples of which include monoethanolamine, diethanolamine, triethanolamine, methyldiethanolamine, diisopropanolamine, diglycolamine and mixtures thereof, and physical hydrogen sulfide solvents, such as N-methylpyrrolidone, dimethyl ether of polyethylene glycol, tributyl phosphate, methanol or mixtures thereof, as well as any mixtures of at least one alkanolamine-based absorbent with at least one physical hydrogen sulfide solvent at any ratio thereof. The alkanolamine containing absorbents are supplied in solution with water. The concentration of the solution of alkanolamine based absorbents and/or physical hydrogen sulfide solvents supplied to the electrochemical cell is preferably from 10 to 100% by weight, depending on the absorbent type.

(24) If necessary, the electrochemical cell may further comprise means for removing the product of the reaction occurring in the electrochemical cell, in particular, means for removing sulfur-containing species such as elemental sulfur and polysulfide ions produced within the cell.

(25) In some embodiments, the electrochemical cell herein disclosed is configured to produce hydrogen from water in the presence of sulfur dioxide as an anode depolarizer and an aqueous feed/electrolyte solution comprising a sulfur dioxide absorbent. Non-limiting examples of sulfur dioxide absorbents include amines, other chemical or physical sulfur dioxide organic absorbents, and mixtures thereof. When in use, the electrochemical cell comprises at least two electrodes connected to an external power supply; in different electrochemical cell designs the electrodes can be separated by the feed/electrolyte solution per se or at least one proton conductive membrane. It is also necessary to ensure supply of the feed/electrolyte solution to the electrochemical cell and withdrawal of the regenerated solution and products of the electrochemical reaction from the cell.

(26) Without wishing to be bound by theory, in some embodiments of the invention, the following reactions are believed to occur in the electrochemical cell (electrolyzer) with the sulfur dioxide rich chemical absorbents and/or physical sulfur dioxide absorbents:
At anode: SO.sub.2 (aq)+2H.sub.2O.fwdarw.4H.sup.++2ē+SO.sub.4.sup.2−.sub.(aq)  (27)
At cathode: 2H.sup.++2ē.fwdarw.H.sub.2(g)  (28)
Overall reaction: SO.sub.2 (aq)+2H.sub.2O.fwdarw.2H.sup.++SO.sub.4.sup.2−.sub.(aq)+H.sub.2(g)  (29)

(27) In eqs (27) and (29), the product of oxidation of SO.sub.2 is written as SO.sub.4.sup.2−, but depending on specific conditions, other products of the general formula H.sub.xSO.sub.y.sup.n−, 0≤x≤2, y=3 or 4, 0≤n≤2, may be formed in addition to or instead of sulfate anion.

(28) The absorbents increase the solubility of the sulfur dioxide in the aqueous solution, thus the oxidation of SO.sub.2 occurs at a much lower voltage than water electrolysis. Due to the “chemical solubility”, the electrochemical oxidation of SO.sub.2 dissolved, for example, in amine-based absorbents is expected to occur at a lower voltage than in the SDE electrolyzer discussed above.

(29) Reference is now made to FIG. 2, which illustrates a second non-limiting embodiment of an electrochemical cell for production of hydrogen in the presence of SO.sub.2 according to the present invention. In this embodiment, the electrochemical cell comprises a frame (1); a proton exchange membrane (PEM) (2); a positive electrode (anode) (3) and a negative electrode (cathode) (4). Each of the anode 3 and the cathode 4 typically consists of an electrically-conductive structure and when the cell is in use, both are connected to an external power supply. In the embodiment shown, one PEM membrane is used; in other embodiments, a plurality of membranes may be used, or the anode and cathode can be separated by the feed/electrolyte solution. The PEM membrane can be made from polymeric, ceramic or other specially elaborated and composite materials, such as Nafion, Polybenzimidazole, Sulfornated Polybenzimidazole (s-PBI), Sulfonated Diels-Alder Polyphenylene, Sulfonated PFCB-BPVE-Tetramer, Silica, Hybrid Silica Nafion nanocomposites etc., which let hydrogen ions (protons) pass through membrane but stop hydrogen gas and other compounds. PEM 2 divides the interior of frame 1 into an anode chamber (1-1) and a cathode chamber (1-2). Anode chamber 1-1 includes an inlet (5) and an outlet (6), and cathode chamber 1-2 includes an outlet (7). In operating mode, inlet 5 is used to admit into anode chamber 1-1 the water and the sulfur dioxide supplied in the solution with absorbent, and the outlet 6 is used to remove from the anode chamber 1-1 the feed/electrolyte solution with products of the reaction (sulfate anions or sulfuric acid). Hydrogen gas generated at the cathode exits the cathode chamber via outlet 7. Note that in embodiments of the invention in which the cathode an anode are separated by the feed/electrolyte solution, there will not be separate anode and cathode chambers.

(30) In some embodiments, the electrochemical cell comprises an inlet to cathode chamber 1-2 for water supply, in order to enhance hydrogen gas removal and for safety. In some embodiments, the water is used as needed for cooling or temperature control. For simplicity and clarity, certain standard elements of PEM electrochemical cell are not shown or described herein (for example anode and cathode collectors, diffusion layers and catalysts which are used in order to increase cell's capacity).

(31) Analogously to the electrochemical cell described above for production of hydrogen gas from H.sub.2S, the proton-conductive separator may contain one or more catalyst layers. In some non-limiting preferred embodiments, the separator comprises an anode-side catalyst selected from the group consisting of platinum, ruthenium, palladium, and mixtures, alloys, and combinations thereof. In some non-limiting preferred embodiments, the separator comprises a cathode-side catalyst selected from the group consisting of platinum, ruthenium, palladium, iridium, aluminum, lead, metal oxides, and mixtures, combinations, and alloys thereof. In some preferred embodiments of the invention, the metal oxide is selected from the group consisting of oxides of palladium, ruthenium iridium, aluminum, and lead, SnO.sub.2, SbO.sub.2, TaO.sub.2, TiO.sub.2, and Ti.sub.4O.sub.7.

(32) If necessary, the electrochemical cell may further comprise means for removing the product of the reaction occurring in the electrochemical cell, which are not removed by withdrawing the feed/electrolyte solution, or which occurs in the cathode chamber (in case of undesirable SO.sub.2 crossover through the PEM), in particular, sulfur compounds.

(33) The sulfur dioxide absorbent supplied to the electrochemical cell according to the invention is preferably either the amine-based and/or other chemical or physical sulfur dioxide organic absorbent, or a mixture thereof, as described above. In this process, the amount of the organic absorbents in the sulfur dioxide absorbent solution can be from 10 to 100 percent by weight depending on the absorbent type. Solutions including any mixtures containing a combination of any of the amines and any other chemical and physical sulfur dioxide organic solvents may also be employed.

(34) In some embodiments of the invention, the method is performed on a system comprising a plurality (stack) of electrochemical cells connected in series. The use of a plurality of cells will enhance the overall electrolysis capability relative to the use of a single cell.

(35) In some embodiments of the invention in which a stack of electrochemical cells is used, the feed/electrolyte solution is circulated through the system. In one non-limiting of the invention, inlet 5 of the first cell in the stack is connected to a source of feed/electrolyte system, and for each succeeding cell in the stack until the last one, outlet 6 of the cell is connected to inlet 5 of a following cell (e.g. the next cell) in the stack. The feed/electrolyte solution may be discarded from the final cell in the stack, or outlet 6 of the final cell can be connected to inlet 5 of the first cell, thereby allowing circulation of feed/electrolyte solution through the stack. If the outlet of the final cell is connected to the inlet cell, then the connection from the source of feed/electrolyte solution to the first cell can be closed after the cells in the stack are full. In embodiments that comprise a stack of electrochemical cells, any connection of the cells to a source and drain of feed/electrolyte solution, whether it permits circulation to and from any or all of them, is considered by the inventor to be within the scope of the invention.

(36) In some embodiments of the invention, the absorbent is regenerated and optionally reused. In some non-limiting embodiments, the absorbent is regenerated by removing the feed/electrolyte solution from the cell and separating the absorbent therefrom. Any means for regenerating the absorbent known in the art may be used.

(37) It shall be understood that the above description is merely illustrative, and the claims cover all modifications or alternatives that could be obvious to a person skilled in the art.