MXPA00009973A - Electrochemical oxidation of hydrogen sulfide - Google Patents

Abstract

Process for gas phase electrochemical oxidation of H2S to sulfur and water or steam using an electrolysis cell (40) having an anode chamber (15, 42) on one side of a solid proton conducting membrane (17) and a cathode chamber (16, 41) on the other side of the membrane. The process comprises the steps of passing H2S-containing gas through the anode chamber to contact a catalytic anode, where it reacts to produce elemental sulfur, protons and electrons. The protons pass through the membrane from the anode chamber to the cathode chamber. An oxygen-containing gas is passed through the cathode chamber to contact the catalytic cathode, where it reacts with protons and electrons to produce water or steam. During the process, both the anode chamber and cathode chamber are maintained at a temperature of at least 120°C and an elevated pressure sufficient to keep the membrane moist. Sulfur is obtained in liquid or vapour form and is removed from the anode chamber while water or steam is removed from the cathode chamber. An electric current can be withdrawn from the anode and cathode. The cell can also be operated in the electrolysis mode to produce sulfur and hydrogen.

Description

"ELECTROCHEMICAL OXIDATION OF HYDROGEN SULFIDE" TECHNICAL FIELD This invention relates to the spontaneous electrochemical conversion of H2S to sulfur and water, with the simultaneous production of electrical energy or in sulfur and hydrogen.

ANTECEDENTS OF THE TECHNIQUE Hydrogen sulfide (H2S) is a corrosive and extremely toxic gas that is present in natural gas wells at concentrations ranging from a few parts per million up to 50 percent or even higher. The hydrodesulfurization of heavy oil and bitumen and coal gasification also produces gas stream containing hydrogen sulfide, as an undesirable by-product. At present, the approach to the removal of H2S has been to destroy it by oxidation in steam and sulfur, and not to use H2S as a source of hydrogen. A number of processes are available for the removal of H2S from natural gas and process gas streams, and to convert it into useful products or - at least harmless products. Most of these methods are multi-stage processes that begin with the chemical or physical absorption of H2S. In practice, H2S is usually removed by contacting the process gas with a thin film of a basic organic solvent. The solvent is regenerated by heating in a second unit, and the flushed H2S is destroyed, using the Claus process well established. In this process, part of the H2S is oxidized yielding SO2 and H2O. The SO2 then reacts with additional stoichiometric amounts of H2S through an alumina-based catalyst, to produce elemental sulfur, water and heat. The total chemical reaction occurs at a temperature of 525 ° C-700 ° C, and can be summarized as follows: 1/3 H S + 1/2 0? 1/3 S02 + 1/3 H20 (1) 2/3 H2S + 1/3 S0? S + 2/3 H20 (2) Net reaction: H2S + 1/2 02? S + H20 + Q (3) Even though the Claus process is exothermic and generates thermal energy, the heat is generally not used and therefore has no economic value. The electrolysis of H2S solutions has been considered as an attractive alternative strategy due to the more favorable thermodynamics compared to the electrolysis of water. Neither this, nor other approaches that recover hydrogen - using thermal catalytic decomposition and membranes for separation, it has still been commercialized, which is partially due to the total net energy input that is required. A much more desirable strategy is to directly oxidize electrochemically the hydrogen that originates from the decomposition reaction of H2S. In this way, a fuel cell using H2S as the feed would generate electrical energy, leaving only sulfur and water as environmentally acceptable products. There is very little information in the literature related to the electrochemical oxidation of the H2S gas phase in a fuel cell. A fuel cell using a fuel containing H2S is described in the North American Patent issued to Pohl et al., Number 3,874,930. The electrolyte was a mineral acid, and the anode consisted of M0S2 or WS2 mixed with a conductive material. A work was recently reported in which zirconia stabilized with yttria and calcite was used as the electrolyte conductor of solid oxygen ion that was operated at 900 ° C. Practical cell voltages were less than 0.9 V at current densities of only a few mA. The problem of producing the undesirable byproduct SO2 has not been eliminated. The potential applications of the solid state, the oxygen ion conductive membranes for the - oxidation of H2S in sulfur, have been described in the North American Patent of Sammells, Number 4,920,015. The same group has investigated the use of mixed solid conductors (oxygen-anion and proton) in a "Claus electrochemical process". The findings indicate the possibility that there is a reforming mechanism to provide hydrogen, which subsequently reacts as a fuel at the anode. There was a significant decrease in the cell voltage when the H2S content in the inert gas was increased. This discovery suggests that elemental sulfur covers the electocatalytic sites and limits the diffusion currents for hydrogen oxidation. Ven Atesan et al., US Pat. No. 4,544,461, used aluminosilicate materials (zeolites) both as proton conductors and catalytic materials in a fuel cell of H2S-O2. The cell temperatures were <370 ° C, which seems to be of crucial importance for the conductivity of zeolite. It was stated that aluminosilicates that can be activated to a satisfactory conductivity by partial removal of water. The maximum electromotive force obtained was 0.35 V. The disadvantage of the design seems to be that the porous zeolite structure can not ensure both a sufficiently high conductivity and gas impermeability. In a related system, LÍ2SO4 was tested as the proton-conducting electrolyte in a fuel cell of H2S-O2 at 700 ° C. From the foregoing description of the prior art, it can be seen that the dissociation of H2S exclusively towards its elements has not previously been achieved with high efficiency. In this way, no economically viable system has existed until now for the electrochemical oxidation of H2S exclusively in sulfur and steam, with the generation of electrical power.

COMPENDIUM OF THE INVENTION One embodiment of the present invention relates to a process for the electrochemical oxidation of gas phase of H2S in sulfur and water or steam, using an electrolysis cell having an anode chamber on one side of a solid proton-conducting membrane and a cathode chamber on the other side of the membrane. The process comprises the steps of passing the gas containing H2S through the anode chamber to contact a catalytic anode, where it reacts to produce elemental sulfur, protons and electrons. The protons pass through the membrane from the anode chamber to the cathode chamber. It passes a gas that - It contains oxygen through the cathode chamber to contact the catalytic cathode, where it reacts with protons and electrons to produce water or steam. During the process, both the anode chamber and the cathode chamber are maintained at a temperature of at least 120 ° C, and a pressure high enough to keep the membrane moist. Sulfur is obtained in the form of liquid or vapor and is removed from the anode chamber while water or steam is removed from the cathode chamber. An electric current can be removed from the anode and the cathode. The solid proton conductive membrane can be produced from a variety of materials, such as perfluorosulfonic acid or polybenzimidazole. A particularly effective proton-conducting membrane is the perfluorosulfonic acid product sold under the trademark Nafion®. The anode and the cathode can be formed from a variety of different materials, such as carbon products and electrodes made of compressed carbon powder that have been found to be particularly effective. These are charged with a metal catalyst, which can be selected from a wide variety of metals, such as Mo, Co, Pt, Pd, Cu, Cr, Ni, Fe, Mn, etc. Preferably, the catalyst except Pt and Pd is in the form of sulfide. The body of the electrolysis cell can also be formed from a variety of materials such as Teflon, a block of carbon, metal, etc. Preferably, the body of the electrolysis cell is metal for operation at high temperature and pressure. A preferred anode catalyst according to the invention is a metal sulfide prepared by the sol-gel technique (ST Srinivasan, P. Kanta Rao, "Synthesis, Characterization and Activity Studies of Carbon Supported Platinum Alloy Catalysts", Journal of Catalysis , 179 (1998) 1-17). Using the sol-gel technique, the metal sulfide is deposited on the carbon in a highly dispersed state. In this way, the particles of the active material are each small and well dispersed throughout the carbon surface. The result of this well dispersed formation of very small particles is an increased surface area of the active catalyst. In addition, each particle remains in intimate contact with the support instead of simply being mixed with the carbon. This affects both the chemistry of the particles and the ability to transfer the electrons and protons within the anode. The basic fuel cell according to the invention has the following configuration: H2S / anode / solid electrolyte / 02 (g) The essential components of the reaction mechanism are the following: H2S anode? S + 2H + + 2e ~ Cathode 1/2 02 + 2H + + 2e ~? H20 Cell H2S + 1/2 02? S + H20 It is also possible in accordance with this invention to operate the cell only in an electrolysis mode to produce sulfur and hydrogen. When operated in the electrolysis mode, the gas that is being fed to the cathode chamber is an inert gas such as argon or nitrogen instead of oxygen. It has been found that the most effective method for operating the electrolysis cell is at temperatures above the sulfur melting temperature, preferably within the range of 125 ° C-165 ° C, and at sufficiently high pressures to ensure the presence of water from the liquid phase inside the Nafion membrane. The pressure to achieve this usually at least is about 0.14 MPa and preferably falls within the range of about 0.14 to 0.41 MPa.

BRIEF DESCRIPTION OF THE DRAWINGS The above further advantages of this invention will be seen upon reading the description of the - preferred embodiments together with reference to the drawings in which: Figure 1 is a schematic depiction of an embodiment of an electrolysis cell to be used in accordance with the invention; Figure 2 is a schematic representation of a further electrolysis cell; Figure 3 is a schematic representation of a tubular electrolysis cell, high pressure, high temperature; Figure 4 is a schematic flow sheet of an experimental electrolysis system; Figure 5 is a trace of the conversion of H2S and the potential as a function of time; Figure 6 is a trace of the conversion of H2S as a function of time at different gas flow rates; Figure 7 is a trace of the potential as a resistance function; Figure 8 is a trace of potential as a function of time at different temperatures and pressures; Y Figure 9 is a trace of the current as a function of applied potential for an electrolysis cell.

- - BEST WAYS TO CARRY OUT THE INVENTION Figure 1 shows an electrolysis cell having body portions 10 and 11, each with a flow inlet connector 12 and a flow outlet connector 13. Each body portion also has a body cavity 14 connected with connectors 12 and 13. The electrodes 15 and 16 are fitted within the recesses in the cavities of the body with the membrane 17 maintained between the electrodes 15 and 16. An alternative design of electrolysis cell, made of a carbon block, is shown in Figure 2. In this embodiment, a pair of carbon blocks 20 and 21 are used to form the body of the electrolysis cell. Slots 22 are provided in the carbon blocks to provide flow to the electrodes 23 and 24 which are maintained between the blocks 20 and 21. A membrane 25 is maintained between the electrodes 23 and 24 to complete the cell. This cell design is usually not adaptable to a wide range of conditions. Shown in Figure 3, a tubular high pressure and high temperature cell. This consists of an external tubular casting body 30 having end insertion pieces 32 to provide flow connectors 33 and 34, which are isolated from the tube 30. The pieces - 32 can be retained in place by end compression nuts, not shown. Mounted coaxially within the tube 30 is a porous metal, eg, a nickel tube 35 of a diameter smaller than the tube 30 so as to provide an annular space 36 between the porous nickel tube 35 and the outer case 30. One layer which comprises a proton-conducting membrane is formed on the outer surface of the nickel tube 35, sealing the pores of the tube. A nickel mesh 37 is wrapped around the tube 35, this mesh holding a metal catalyst. The mesh is wrapped tightly in the tube using a nickel wire 38 which also acts as the electrical contact. This embodiment provides a generally tubular configuration design with a tubular membrane. An anode catalyst is on the outside of the membrane and a cathode catalyst is on the membrane's interior. Therefore, the annular space 36 is the anode chamber and the central space 39 is the cathode chamber. Figure 4 shows an experimental system for the electrochemical oxidation of H2S. The core of this system is an electrochemical cell 40 which includes a cathode chamber 41 and an anode chamber 42 divided by a membrane. The cell is placed inside a furnace 43 to maintain a constant temperature. That temperature - - it is controlled by means of a thermoelectric pair 44 and a temperature controller 45 for a heating system (not shown). The gas is fed to the cathode chamber by means of a feed line 46 with the flow being controlled by the flow controller 47 and a pressure gauge 48. The cathode chamber is also included within this gas feed system. heated steam saturator 49 and a current transformer 50, The gas to the anode chamber is fed through line 51 with the flow also being controlled by means of a flow controller and pressure gauge. To control the electrochemical cell, a voltmeter 52, a resistor box 53 and a potentiostat 54 are fixed thereto. The product material from the anode chamber is discharged through line 55 through the trap 56. and the regulated backpressure valve 57. The discharge is preferably placed so that the liquid sulfur can be drained by gravity flow. In this way, the cell of preference is placed in a vertical configuration. A three-dimensional valve 58 allows discharge either through the gas chromatograph 59 or the vent 60.

- The discharge from the cathode chamber 41 is through the line 61 which also passes through a trap 56 and a regulated back pressure valve 57. This line is also connected either to the gas chromatograph 59 or the conduit of ventilation 60 through a three-dimensional valve 58.

Example 1 Catalytic electrodes were prepared using the active catalysts of Pd, Pt and M0S2. The materials of the catalysts were prepared consisting of: (a) 10 percent Pt / carbon Vulcan XC-72R (Alfa, Aesar) (b) 20 percent Pd / activated carbon powder, not reduced (Alpha, Aesar) (c) MoS2 / black powder (Alfa, Aesar) These were mixed with 35 percent Teflon-treated carbon black (Shawinigan C-100 acetylene carbon black, Chevron Chemical Corp.) to produce the electrodes. The mixture was then compressed in a mold to form the electrode. The anodes and catalytic cathodes had the compositions shown in Table 1, which is presented below.

TABLE 1 Sample Catalysts Catalyst Catalyst node Pd anode Catalyst P.02 12.22% of Pd / C 2.16% of Pt / C P.03 7.83% Pd / C 2.55% Pt / C P.04 8.35% 1from: Pd / C 2.16% from Pt / C P.05 9.94% «de: Pd / C 2.46% Pt / C P.12 9.54% 1from: Pd / C 2.37% from Pt / C P.14 9.88% 1of: Pd / C 2.05% of Pt / C M0S2 Catalysts of the node P.06 66.52% of MoS2 / C 2.52% of Pt / C P.07 62.47% of M0S2 / C 2.27% of Pt / C P.08 62.04% of M0S2 / C 2.41% of Pt / C P.09 65.78% of M0S2 / C 2.75% of Pt / C P.10 67.31% of M0S2 / C 2.22% of Pt / C P.ll 66.27% of M0S2 / C 2.23% of Pt / C P.13 60.18% of MoS2 / C 2.20% of Pt / C Pt Catal: Anode zeros P.01 5.96% Pt / C 2.16% Pt / C P.15 4.53% Pt / C 2.08% Pt / C - The membrane-electrode assemblies, which are the main components of the system, were obtained by pressing the psosos electrode materials on both sides of a proton exchange membrane. The membrane used was a commercially available perfluorosulfonic acid membrane Nafion® from DuPont.

Example 2 A test was carried out in the electrolysis system of Figure 4 to determine the dependence of the potential and conversion of H2S as a function of temperature. It was operated as a fuel cell of H2S / O2, with an anode catalyst of 60.24 percent M0S2 / C and a cathode catalyst of 2.41 percent Pt / C (P.08 above). The cell was operated at a pressure of 0.36 MPa and at variable temperatures up to 150 ° C. The results are illustrated in Figure 5, which clearly shows the favorable effect of the operation at high temperatures, curve (a) showing the conversion and (b) showing the potential.

Example 3 - The ratio of H2S conversion to an anode compartment feed gas flow rate was studied in the system of Figure 4 during operation as a fuel cell of H2S / O2 at conditions of 145 ° C and 0.36 MPa. For this test, a catalyst combination of 9.88 percent Pd / C anode of 2.05 percent Pt / C and cathode (P.14) was used from Table 1. The tests were carried out at flow rates of 4 cubic centimeters per minute, 9 cubic centimeters per minute and 16 cubic centimeters per minute and the results obtained are shown in Figure 6, with curve (a) being 4 cubic centimeters per minute, (b) 9 cubic centimeters minute and (c) of 16 cubic centimeters per minute.

Example 4 In order to determine the sustainable operating capacity of the H2S / O2 fuel cell, tests were carried out on the sisstema of Figure 4 over a prolonged period while the potential is measured as a function of the resistance in the external circuit. The anode catalyst combination of 7.83 percent Pd / C and cathode of 2.55 percent Pt / C (P.03) from Table 1 was used and the cell from - The fuel was operated at a temperature of 125 ° C and a pressure of 0.275 MPa. The results are shown in Figure 7 with curve (a) being for the fresh catalyst and curve (b) after being operated for 36 hours. The results clearly demonstrate the reliability of the operation of this system at high temperature, and high pressure.

Example 5 An additional test was carried out in the system of Figure 4 to examine the relationship of the potential in a fuel cell as a function of the operating time. For this test, the results were compared to operate the H2S / O2 fuel cell at room temperature and atmospheric pressure in one case and at 145 ° C and 0.345 MPa in the other case. The test at room temperature was carried out using an anode catalyst of 80 percent M0S2 / C, while the test at elevated temperature and pressure was carried out using an anode catalyst of 62.47 percent M0S2 / C and a cathode catalyst of 2.27 percent Pt / C in combination (P.07) from Table 1. The results are shown in Figure 8, with curve (a) at room temperature and atmospheric pressure and (b) a 145 ° C and 0.345 MPa. These results clearly show the reliability of operation at high temperature, high pressure.

Example 6 The system of Figure 4 was operated in the electrolysis mode to determine the ratio of the current as a function of time through a period of prolonged operation to an applied constant potential. For this test, the anode catalyst of 7.83 percent Pd / C and the cathode catalyst of 2.55 Pt / C (P.03) of Table 1 was used with the cell being operated at a temperature of 125 ° C and at a pressure of 0.275 MPa. A constant potential of 600 m V was applied. The cell was operated for 30 hours with the H2S feeding into the anode chamber and the atmosphere in the cathode compartment changing to nitrogen for the electrolysis mode. The results are shown in Figure 9, which show an average current capable of holding about 6.5 mA.

Example 7 A series of additional catalysts was prepared and tested in an H2S / O2 fuel cell. A laboratory cell having a circular design with an active area of approximately 3 square centimeters was used. A stainless steel mesh was used as a support for the membrane electrode assembly and as current collectors. The tests were carried out using both commercially obtainable materials and specially synthesized catalysts. 1. Preparation of the Catalyst a) MSX / C Carbon sulphide metal catalysts, MoSx / C and CoSx / C (initial composition x ~ 2.5 in each case), were prepared by a sol gel method combined with a technique of wet impregnation. The method will be explained with respect to MoSx / C. The Carbon Powder (Shawinigan C 100 Acetylene Carbon Black, Chevron Chemical Corp.) was suspended in a 2 propanol grade (Fisher Scientific, HPLC) and stirred for 15 minutes. After purging the reaction vessel containing the suspension with N2, molybdenum isopropoxide (V) (Alfa AEsar, 99.6 percent metal base, 5 weight percent / volume in 2 propanol) was added to the mixture. It was stirred for an additional 15 minutes and then hydrogen sulfide gas was introduced into the mixture. When the mixture was gelled, the H2S supply was stopped and the reaction vessel was closed. The gel was aged for 48 hours and then opened in air to evaporate the solvent. The catalyst contains 10 weight percent molybdenum. b) MoCoSx / C Dry MoSx / C was used as a substrate for the CoSx deposition (x ~ 1.5). Then the cobalt sulphide was precipitated into the substrate either by wet impregnation or wet gel combined impregnation method. The precursor for the wet impregnation synthesis was acetone acetyl Co (III) (Aldrich, 98 percent). An appropriate amount of the reagent was dissolved in acetone (Fisher Scientific, HPLC grade). MoSx was added to the solution and stirred for 30 minutes. The H2S gas was then bubbled through the suspension at 5 milliliters per minute for 1 hour, after which the suspension was closed and allowed to settle for 72 hours. The clear solution formed above the precipitated material was decanted and the precipitate was filtered. It was vacuum filtered through a Buchner funnel using Whatman # 40 filter paper. The precipitated cobalt / carbon sulfide material was washed with acetone first, and then with approximately 200 milliliters of deionized water, was placed on a glass plate and allowed to dry in an oven at 105 ° C overnight. The catalyst prepared contained 30 percent Co. CoSx precipitation in MoSx / C by combined sol gel and wet impregnation methods was carried out in the same manner as MoSx / C, described above. The reagent used was Co (V) methoxyethoxide (Alfa AEsar, 99.5 percent metal base, 5 weight percent / volume in 2 methoxy ethanol). c) CuFeSx / C Carbon iron sulfide catalyst based on carbon was prepared by the wet precipitation impregnation method. - The catalyst was synthesized in an aqueous acidic solution, pH = 5, Cu (N03) 2 * 21/2 H2S (Fisher Scientific, 98 percent), FeCl3 (Alpha, AEsar, 98 percent, anhydrous) and sulfur of hydrogen. The reagents, cupric nitrate and iron chloride, were dissolved in water. The pH was adjusted to 5 with IN HCl. The carbon powder was added to the solution (Carbon Black Acetylene Shawinigan CB 100, Chevron Chemical Co. ) and 5 milliliters of ethanol (Fisher Scientific, HPLC). The suspension was stirred for 30 minutes before the H2S was introduced. The gas bubbled. Then, the reaction vessel was closed and left for 72 hours so that the sulfides were precipitated. The supernatant liquid that formed was decanted and the sediment was filtered under vacuum. It was mixed with 3x100 milliliters of deionized water, until the filtrate showed a pH = 7. The carbon-supported catalyst was dried in an oven at 105 ° C overnight, d) 40 percent Pt / C This catalyst was prepared by the wet-impregnation method. A commercially available catalyst, 10 percent Pt on carbon Vulcan XC 72R (Alfa AEsar) was used as a support for a new catalyst with a higher Pt load. In this way, an appropriate amount of 10 percent Pt / C in acetone was suspended and stirred for 15 minutes. The solution of acetylacetone Pt (II) (Strem Chemicals, 98 percent) in acetone was added to the suspension. It was stirred on a hot plate at a temperature of about 50 ° C until the meniscus disappeared. The mixture was allowed to partially dry in air where occasionally it was stirred with a glass rod. To dry it completely, it was placed in an oven at 80 ° C for 1 hour. The 40 percent Pt / C catalyst was ground in a thin mortar. 2. Preparation of the electrodes The electrodes of the H2S / O2 fuel cell, the anode and the cathode, consist of a chemically active component, a catalyst, and an electrically conductive component, the carbon powder. In addition, polytetrafluoroethylene (Teflon®, Aldrich, 60 weight percent dispersion in water) was added to increase the hydrophobicity of the electrodes and their mechanical properties. Two methods were used for the electrode preparations: pressing the dry powders and depositing the powder suspension by filtration. The different electrodes and their methods of preparation are indicated in Table II. a) Preparation of electrodes by pressing the powder All the anodes prepared by pressing the powder were made from the same amount of commercially available catalysts and carbon black as teflonized. The procedure for the carbonization is described above. For the described electrodes, the same batch of teflonized carbon powder at 35 weight percent was used (Shawinigan Aceite Carbon Black CB 100, Chevron Chemical Co.). Therefore, 60 weight percent of a catalyst and 40 weight percent of the teflonized carbon powder were completely mixed in a beaker with a glass rod. The mixture was pressed into a 25.4 mm stainless steel die at 14 MPa pressure. The thickness of the anode is approximately 0.5 millimeter. The cathodes prepared by pressing the powder are the same for all described membrane electrode assemblies (MEA). They were prepared from a homogeneous mixture of 10 percent Pt / C and 35 percent teflonized carbon. They were passed in the same matrix under the same pressure as the anodes. The thickness of the cathodes is 0.5 mm. b) Preparation of electrodes by filtration. The thickness of the electrodes prepared by this method is < 0.050 mm In addition, a carbon cloth used as a substrate for electrode deposition is a current collector at the same time. Having a current collector and an anode is this narrow contact is advantageous since the accumulation of liquid sulfur between the electrode and the collector is prevented. • The electrodes consist of teflonized catalyst. Tephonization of the catalyst, either from metal sulphides supported on the carbon used for the anodes or 40 percent Pt / C used for the cathodes, was carried out in the same manner as the carbon powder teflonization described above. The prepared suspensions of the teflonized catalysts were deposited on the carbon cloth (GC 80 graphite cloth, Electrosynthesis Co.) which are substrates by vacuum filtration. The deposited layer was flattened, dried in air and placed in an oven at a temperature of about 350 ° C for 30 minutes. 3. Preparation of the Membrane Electrode Assembly (MEA) A solid polymer membrane of Nafion® 117 (Aldrich) was used as a proton-conducting electrolyte. Before ligating to the electrodes, it was treated in concentrated nitric acid for 30 minutes, washed with deionized water and soaked in IN H2SO4 for 30 minutes. The membrane was again washed in deionized water and allowed to air dry. The electrodes were coated with dissolved Nafion® (Aldrich, 5 weight percent Nafion® in an alcohol water solution) before they were fixed to the membrane. Only one side of each of the electrodes was covered with the Nafion® solution and then allowed to dry. The electrodes were hot pressed to the membrane under pressure of 0.5 MPa and at a temperature of 130 ° C. Results The anodes and cathodes were then tested in a laboratory cell. The fuel cell was operated on pure hydrogen sulfide (Liquid Air, 99.8 percent H2S) and pure oxygen (Liquid Air, 99.8 percent O2) at gas pressure of 3 atmospheres (0.3 MPa) and 130 ° C. Only oxygen was passed through the water bath in order to keep the membrane moist. The electrical direct current parameters of the cell were measured for each MEA. The current voltage characteristic of the cell was measured at regular intervals (ie, hourly). Meanwhile, the cell was operated in an open circuit mode. During a long-term experiment, the cell was operated at a constant load resistance of 10. The experiments were carried out for 4 to 48 hours under this load. The results of the open-circuit potential (Eoc), the electric current (J) was measured at 10 and at a maximum power (Wmax) for the different sets of membrane electrode is presented in Table III. From these results, it can be seen that an anode catalyst prepared by the sol gel technique provides a generally improved operation of the membrane electrode assembly, as compared to a catalyst prepared as a simple mixture. This is particularly important with respect to current density.

Table II Catalyst content in the electrodes and the ways of catalyst and electrode preparations (commercially available CA, synthesized in the LAB in our laboratory, F filtration, PP pressed powder).

MEA CONTENT PREPARA- PREPARA- CONTENT PREPARA- PREPARA TION OF C ONION OF C ALL TION OF CION (mg / cm2) CATALYANODO (mg / cm2) CATALI- CÁTODO ZADOR DE ZADOR DE ÁNODO CÁTODO B 2 60 CUSCA PP 4 Pt / C PP CA B 3 60 Cr2S3 CA PP 4 Pt / C PP CA B 4 60 WS2 CA PP 4 Pt / C PP CA B 5M 60 NiS2 CA PP 1.2 Pt / C F LAB B 6 60 FeS CA PP 4 Pt / C PP CA GDE 8 1.1 MoS? / C LAB F 1.2 Pt / C F CA GDE 14 5.1 MoCoS? / C LAB F 1.2 Pt / C F LAB GDE 16 5.0 CuFeS? / C LAB F 1.2 Pt / C F LAB GDE 21 5.8 MoCoS? / C LAB F 1.2 Pt / C F LAB GDE 22 6.2 CoS? / C LAB F 1.2 Pt / C F LAB Table III MEA Eoc (mV) J (mA / cm2) Wmax (mW / cm2) B 2 656 72 B 3 496 144 21 B 4 460 44 B 5M 758 176 31 B 6 552 56 GDE 699 30 GDE 14 608 104 11 GDE 16 525 110 12 GDE 21 713 200 40 GDE 22 585 < 1

Claims (13)

CLAIMS:

1. A process for the electrochemical oxidation of H2S gas phase in sulfur and water or steam using an electrolysis cell having an anode chamber on one side of a solid proton conducting membrane and a cathode chamber on the other side of the membrane, the process involves: passing the gas containing H2S through the anode chamber to contact a catalytic anode, where it reacts to produce elemental sulfur, protons and electrons; passing the protons through the membrane of the anode chamber to the cathode chamber; and either passing a gas containing oxygen through the cathode chamber to contact a catalytic cathode, where it reacts with the protons and electrons producing water or forming hydrogen in the cathode chamber; characterized in that both the anode chamber and the cathode chamber are kept at a temperature of at least 120 ° C and a high enough pressure to keep the membrane moist and the liquid sulfur is removed from the anode chamber and the water or the hydrogen are removed from the cathode chamber.

2. A process according to claim 1, characterized in that an oxygen-containing gas is passed through the cathode chamber to contact a catalytic cathode, where it reacts with the protons and electrons producing water or steam and removing the water or steam from the cathode chamber.

3. A process according to claim 1, characterized in that the hydrogen is formed in the cathode chamber.

4. A process according to claim 3, characterized in that the cathode chamber comprises an inert gas atmosphere.

5. A process according to any of claims 1 to 4 characterized in that an electric current is removed from the anode and the cathode.

6. A process according to claim 1, characterized in that the anode catalyst includes at least one metal which is selected from the group consisting of Mo, Co, Pt, Pd, Cu, Cr, W, Ni, Fe and Mn .

7. A process according to any of claims 1 to 6, characterized in that the catalytic anode is formed from the pressed carbon powder containing the catalyst.

8. A process according to any of claims 1 to 6, characterized in that the anode catalyst is formed by the sol gel technique.

9. A process according to claim 8, characterized in that the catalyst is selected from Mo, Co. Cu, Cr, W, Ni, Fe, Mn, or a combination thereof.

10. A process according to any of claims 1 to 9, characterized in that the anode and cathode chambers are maintained at a temperature within the range of 125 ° C to 165 ° C and a pressure of at least 0.14 MPa, sufficient to keep the membrane in a wet state.

11. A process according to any of claims 1 to 10, characterized in that the membrane is formed of perfluorosulfonic acid or polybenzimidazole.

12. A process according to any of claims 1 to 11, characterized in that the cathode is also formed of pressed carbon powder loaded with a catalyst.

13. A process according to claim 12, characterized in that the catalyst is platinum.