Production of hydrogen from hydrogen sulfide assisted by dielectric barrier discharge

Hydrogen production by non-thermal plasma (NTP) assisted direct decomposition of hydrogen sulfide (H₂S) was carried out in a dielectric barrier discharge (DBD) reactor with stainless steel inner electrode and copper wire as the outer electrode. The specific advantage of the present process is the direct decomposition of H₂S in to H₂ and S and the novelty of the present study is the in-situ removal of sulfur that was achieved by operating DBD plasma reactor at ∼430 K. Optimization of various parameters like the gas residence time in the discharge, frequency, initial concentration of H₂S and temperature was done to achieve hydrogen production in an economically feasible manner. The typical results indicated that NTP is effective in dissociating H₂S into hydrogen and sulfur and it has been observed that by optimizing various parameters, it is possible to achieve H₂ production at 300 kJ/mol H₂ that corresponds to ∼3.1 eV/H₂, which is less than the energy demand during the steam methane reforming (354 kJ/mol H₂ or ∼3.7 eV/H₂).     

Development of Pd-based membranes as hydrogen diffusion anodes

Pd-based membranes have been prepared by Pd electroless deposition on porous stainless steel substrate and their structure, composition, morphology and thickness were analyzed by X-ray diffraction (XRD), EDS and scanning electronic microscopy (SEM). The performance of these membranes as hydrogen diffusion electrodes was evaluated in a three-electrode cell in alkaline medium. The activity towards hydrogen oxidation was high at the beginning of the experiment, but it significantly decreased with time. The major cause of this phenomenon has been attributed to the slow entry of hydrogen at the H₂/Pd interface. Even so, the technical feasibility of using these membranes as gas diffusion electrodes (GDE) has been proven.     

Stability and hydrogen permeation behavior of supported platinum membranes in presence of hydrogen sulfide

Chemical stability for hydrogen sulfide of a platinum composite membrane, consisting of a platinum layer supported on a porous alumina tube by a CVD technique, was evaluated in comparison with a palladium composite membrane. These composite membranes gave high fluxes comparable to that of a reported palladium composite membrane prepared by an electroless-plating technique, as well as high ideal permselectivity for hydrogen over nitrogen, typically 240 for palladium and 210 for platinum at 773 K. When these composite membranes were in contact with gas stream including hydrogen sulfide, their hydrogen permeability declined rapidly. Many cracks were formed on the surface metallic layer of the palladium composite membrane, so that other gases besides hydrogen permeated mainly through the cracks formed. On the other hand, cracks were hardly formed for the platinum composite membrane. It was reported that the lattice constant of palladium was expanded from 0.39 to 0.65 nm by sulfidation of the metallic layer, but that of platinum was slightly changed from 0.39 to 0.35 nm. The difference in the expansion of lattice constant may affect structural change and rupture phenomena of these composite membranes. After the sulfurized platinum composite membrane was treated with pure oxygen flow, the hydrogen permeability was recovered up to 50% of that of the fresh membrane.     

沼气中硫化氢气体的生物处理法

沼气中硫化氢的存在限制了沼气能源的推广。文章阐述了沼气生物脱硫法的原理、方法和可行性,介绍了该方法在国内外的研究发展现状。     

Strain gradient-induced diffusion of hydrogen in palladium and nickel membranes

The “uphill” diffusion of hydrogen during permeation through flat sheets of palladium and nickel has been studied by an electrochemical permeation method at 303 K. For both annealed and “as cold rolled” Pd samples, uphill diffusion effects on hydrogen absorption and desorption have been observed over a range of initial hydrogen contents from about H/Pd = 0.01, i.e. near or slightly less than the _max composition, up to H/Pd = 0.25–0.3. The occurrence of a non-Fickian component of permeation flux has been associated with temporary formation of lattice volume differences across the ( + β)/β and ( + β)/ interfaces during absorptions and desorptions, respectively. Influences of the magnitudes of galvanostatic hydrogen fluxes and of the membrane thickness on the uphill effects were examined. Analogous uphill effects were observed in similar studies with nickel membranes also in both annealed and “as cold rolled” states, which were much larger than those observed for palladium.     

Production of hydrogen and nanofibrous carbon by selective catalytic decomposition of propane

The process of production of highly concentrated CO_x-free hydrogen and nanofibrous carbon (NFC) by catalytic propane decomposition on Ni and Ni–Cu catalysts (different in active phase composition) at relatively low temperatures (400–700 °C) was investigated. The bimetallic Ni–Cu catalysts showed significantly higher propane conversion and longer lifetime than monometallic Ni catalyst. The Ni (50 wt.%)–Cu (40 wt.%)/SiO₂ catalyst exhibited the best activity and selectivity at 600 °C. Total hydrogen yield of 60.8 mol H₂/g_cat (during 24 h time on stream) and the total H₂:CH₄ ratio of 8.4 were obtained during propane decomposition under these optimal conditions. The possible reaction scheme of propane decomposition over Ni-based catalysts and the reasons of increasing the selectivity of hydrogen are discussed.     

Modelling of hydrogen production from hydrogen sulfide in geothermal power plants

Geothermal power plants emit high amount of hydrogen sulfide (H₂S). The presence of H₂S in the air, water, soils and vegetation is one of the main environmental concerns for geothermal fields. There is an increasing interest in developing suitable methods and technologies to produce hydrogen from H₂S as promising alternative solution for energy requirements. In the present study, the AMIS technology is the invention of a proprietary technology (AMIS^® - acronym for “Abatement of Mercury and Hydrogen Sulfide” in Italian language) for the abatement of hydrogen sulphide and mercury emission, is primarily employed to produce hydrogen from H₂S. A proton exchange membrane (PEM) electrolyzer operates at 150 °C with gaseous H₂S sulfur dimer in the anode compartment and hydrogen gas in the cathode compartment. Thermodynamic calculations of electrolysis process are made and parametric studies are undertaken by changing several parameters of the process. Also, energy and exergy efficiencies of the process are calculated as % 27.8 and % 57.1 at 150 °C inlet temperature of H₂S, respectively.     

Recovery of hydrogen from hydrogen sulfide with metals or metal sulfides

The following two types of reactions were investigated for the recovery of hydrogen from hydrogen sulfide: Type 1 H₂S → H₂ + S⁰, Type 2 H₂S + O₂ → H₂ + SO₂ Each type of reaction is constructed by a two-step cycle, in which H₂S is reacted with metal or metal sulfide and then the resulting sulfide undergoes thermal decomposition or oxidation. Ag₂S, FeS, Co₉S₈, Ni₃S₂, and the double sulfide CuFeS₂ were examined in the former type of reaction, while Ag, Cu, Ni, liquid Pb, and liquid BiAg alloy were used as an intermediate in the latter.     

Thermochemical production of hydrogen from hydrogen sulfide with iodine thermochemical cycles

With the goal of eventually developing a replacement for the Claus process that also produces $H_2$, we have explored the possibility of decomposing hydrogen sulfide through a thermochemical cycle involving iodine. The thermochemical cycle under investigation leverages differences in temperature and reaction conditions to accomplish the unfavorable hydrogen sulfide decomposition to $H_2$ and elemental sulfur over two reaction steps, creating and then decomposing hydroiodic acid. This proposed process is similar to ideas put forth in the 1980s and 1990s by Kalina, Chakma, and Oosawa, but makes use of thermochemical hydrogen iodide decomposition methods and catalysts rather than electrochemical or photoelectrochemical methods.Process models describing a potential implementation of this thermochemical cycle were created. Motivated by the process model results, experimentation showed the possibility of using alternative solvents to dramatically decrease the energy requirements for the process. Further process modeling incorporated these alternative solvents and suggests that this theoretical hydrogen sulfide processing unit has favorable economic and environmental properties.     

Advances in hydrogen selective membranes based on palladium ternary alloys

Hydrogen containing a minimum amount of contaminants is required for its application in fuel-cell technology. For this purpose, palladium and palladium binary alloy membranes have been widely studied in the last decades due to their ability to selectively permeate hydrogen. The scope of this review is to provide an in-depth analysis of the research on Pd-based ternary alloys and their application as hydrogen separation membranes with a special focus on the PdAgAu, PdCuAg, and PdCuAu systems. The combination of these particular elements - Cu, Au, Ag - can improve hydrogen permeability and chemical resistance. Correlations between structural, surface and permeation properties of the ternary alloys under pure hydrogen and gas mixtures are extensively discussed. A general correlation between hydrogen permeability and the lattice parameter is proposed. In particular, the surface segregation behavior is analyzed for these ternary alloys even after being exposed to CO, CO₂, and H₂S. Further research is needed to develop membranes with improved long-term stability.     

生物法脱除沼气中硫化氢的研究进展

生物脱硫是一种新兴的脱硫方法,在一定条件下通过微生物的代谢作用将硫化氢转化为单质硫,既解决了传统脱硫方法的污染问题,又可以回收硫资源,实现了环保和低成本脱硫,发展前景十分广阔。文章介绍了脱硫微生物以及生物脱硫的机理,综述了近年来国内外沼气生物脱硫技术的研究进展,并对今后的研究方向做了一定的展望。     

High temperature solar thermochemical processing—hydrogen and sulfur from hydrogen sulfide

Sunlight, concentrated to high intensities, has a rarely recognized potential for adding process heat to reactors at high temperatures. Hydrogen sulfide is a by-product of the sweetening of fossil fuels. In this paper, we use, as an example, the production of hydrogen and sulfur from hydrogen sulfide as a device for showing how solar processing might be considered as a successor to a currently used industrial process, the Claus process. We conclude that this and other processes should be explored as means of using as well as storing solar energy.     

Hydrogen and sulfur from hydrogen sulfide—II. Ambient temperature electrolysis using oxidation of hydrogen sulfide by air as the prime energy source

Hydrogen sulfide recovered from the sweetening of fossil fuels or sought as a mineral for its intrinsic value might be converted, in an electrolytic process which uses atmospheric oxygen, into pipeline pressure hydrogen and sulfur. Such a process may be an alternative to the Claus Process, which recovers only sulfur and uses the hydrogen wastefully. It is also suggested that electrolysis provides a mechanism by which other gaseous products, as well as hydrogen, may be brought to pipeline pressures easily.     

Graphite coating on alumina substrate for the fabrication of hydrogen selective membranes

Development of composite membranes is a suitable alternative to improve the hydrogen flux through palladium membranes. The porous substrate should not represent a barrier to gas permeation, but the roughness of its surface should be sufficiently smooth for the deposition of a thin and defect-free metal layer. In this study, the performances of the modification of the outer surface of an asymmetric alumina hollow fibre substrate by the deposition of a graphite layer were evaluated. The roughness of the substrate outer surface was reduced from 120 to 37 nm after graphite coating. After graphite coating, the hydrogen permeance through the composite membrane produced with 2 Pd plating cycles was of 1.02 × 10^?3 mol s^?1 m^?2 kPa^?1 at 450 °C and with infinite H₂/N₂ selectivity. Similar hydrogen permeance was obtained with the composite membrane without graphite coating, also at infinite H₂/N₂ selectivity, but 3 Pd plating cycles were necessary. Thus, graphite coating on asymmetric alumina hollow fibres is a suitable alternative to reduce the required palladium amount to produce hydrogen selective membranes.     

A novel approach to ammonia synthesis from hydrogen sulfide

There are a number of shortcomings for currently-available technologies for ammonia production, such as carbon dioxide emissions and water consumption. We simulate a novel model for ammonia production from hydrogen sulfide through membrane technologies. The proposed production process decreases the need for external water and reduces the physical footprint of the plant. The required hydrogen comes from the separation of hydrogen sulfide by electrochemical membrane separation, while the required nitrogen is obtained from separating oxygen from air through an ion transport membrane. 10% of the hydrogen from the electrochemical membrane separation along with the separated oxygen from the ion transport membrane is sent to the solid oxide fuel cell for heat and power generation. This production process operates with a minimal number of processing units and in physical, kinetic, and thermal conditions in which a separation factor of ~99.99% can be attained.     

Mechanism for SOFC anode degradation from hydrogen sulfide exposure

Recent results on solid oxide fuel cells with Ni/YSZ and Ni/GDC anodes reveal a mechanism for permanent performance degradation due to hydrogen sulfide exposure. Our results confirm the temporary performance decline observed by others but also reveal a mechanism for the long term permanent degradation. We find that hydrogen sulfide leads to nickel migration and depletion in the anode, thereby compromising electrical conductivity and cell performance.     

Steam reformation of hydrogen sulfide

A modified version of the Sulfur–Iodine cycle, here called the Sulfur–Sulfur Cycle, offers an all-fluid route to thermochemical hydrogen and avoids implications of the corrosive HI–H₂O azeotropic mixture:

equation(1)

4I_2(l) + 4SO_2(l) + 8H₂O_(l) ↔ 4H₂SO_4(l) + 8HI_(l) (120 °C)

equation(2)

8HI_(l) + H₂SO_4(l) ↔ H₂S_(g) + 4H₂O_(l) + 4I_2(l) (120 °C)

equation(3)

3H₂SO_4(g) ↔ 3H₂O_(g)+3SO_2(g) + 1½O_2(g) (850 °C)

equation(4)

H₂S_(g) + 2H₂O_(g) ↔ SO_2(g) + 3H_2(g) (900–1500 °C)