Hydrogen production from hydrogen sulfide in a packed-bed DBD reactor

The effect of different reactor packing materials on the nonthermal plasma (NTP) assisted decomposition of hydrogen sulfide (H₂S) in a coaxial dielectric barrier discharge (DBD) reactor has been described in the present investigation. The packing materials studied include ceramic beads, glass material with different geometries like spherical (glass beads), hollow cylinder (glass tubes) and honeycomb (glass wool), and for comparison the reaction was carried out in the absence of any packing material. The packing material studied in the present work do not exhibit any catalytic activity in the traditional sense; however, they do have different dielectric constants and morphologies that may influence the plasma discharge behavior and may also affect the residence time of the gas molecules in the discharge zone. From the experimental results, it has been found that the ceramic pellets and hollow cylindrical glass material packed reactor showed better performance for H₂S decomposition into H₂ and S.     

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.     

Liquid hydrogen production via hydrogen sulfide methane reformation

Hydrogen sulfide (H₂S) methane (CH₄) reformation (H₂SMR) (2H₂S + CH₄ = CS₂ + 4H₂) is a potentially viable process for the removal of H₂S from sour natural gas resources or other methane containing gases. Unlike steam methane reformation that generates carbon dioxide as a by-product, H₂SMR produces carbon disulfide (CS₂), a liquid under ambient temperature and pressure—a commodity chemical that is also a feedstock for the synthesis of sulfuric acid. Pinch point analyses for H₂SMR were conducted to determine the reaction conditions necessary for no carbon lay down to occur. Calculations showed that to prevent solid carbon formation, low inlet CH₄ to H₂S ratios are needed. In this paper, we analyze H₂SMR with either a cryogenic process or a membrane separation operation for production of either liquid or gaseous hydrogen. Of the three H₂SMR hydrogen production flowsheets analyzed, direct liquid hydrogen generation has higher first and second law efficiencies of exceeding 80% and 50%, respectively.     

The exploitation of hydrogen sulfide for hydrogen production in geothermal areas

Hydrogen is a valuable energy resource and it is widespread in nature. As a matter of fact, researches on hydrogen production are currently experiencing an increasing interest from scientists around the world since this resource is clean and renewable. Several methods of producing hydrogen have been developed in industrialized countries such as the United States of America and Germany.This paper is interested in the process by which hydrogen sulfide of geothermal areas is exploited for hydrogen production. In fact, research advances in this field have concluded that hydrogen sulfide of geothermal resources can contribute significantly and economically in the process of hydrogen generation.The present paper was principally conducted from a literature study and a synthesis of works achieved in recent years in order to highlight the various aspects of hydrogen production from hydrogen sulfide and particularly to study the possibility of the exploitation of Algeria’s thermal resources in this field.     

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)

     

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.     

Recovery of hydrogen from hydrogen sulfide by indirect electrolysis process

Recovery hydrogen from hydrogen sulfide is an effective way of utilizing exhaust gas. In this paper, removal of hydrogen sulfide by indirect electrochemical process was studied using acidic aqueous solution of Fe³⁺/Fe²⁺ as the electrochemical intermediate. Solid polymer electrolyte was applied to hydrogen production by indirect electrolysis of H₂S, in which the anode was graphite cloth, the cathode was the platinized graphite cloth, and the membrane was proton exchange membrane. The results of electrolysis experiments showed the relationship of current density as a function of electrolytic voltage at constant flow rate of electrolyte, temperature, and electrolyte composition. The effect of the cathode liquid velocity on current density was small. When the flow rate of anode electrolyte was greater than 200 L/hr., the current density tended to be stable. When [Fe³⁺]>0.20 mol/L, the concentrations of Fe²⁺ and Fe³⁺ ions in the anode solution had no significant impact on the current density. The current density gradually increased with temperature. In the electrolytic process of hydrogen production, the Fe²⁺ ions diffused from the anode to the cathode. The amount of diffusing Fe²⁺ ions gradually increased with time. The effect of Fe²⁺ ions diffusion from anode to cathode on hydrogen production was discussed.     

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).     

Effective use of hydrogen sulfide and natural gas resources available in the Black Sea for hydrogen economy

In this article, we propose a novel system to effectively deploy an integrated fuel processing system for hydrogen sulfide and natural gas resources available in the Black Sea to be used for a quick transition to the hydrogen economy. In this regard, the proposed system utilizes offshore wind and offshore photovoltaic power plants to meet the electricity demand of the electrolyzer. A PEM electrolyzer unit generates hydrogen from hydrogen sulfide that is available in the Black Sea deep water. The generated hydrogen and sulfur gas from hydrogen sulfide are stored in high-pressure tanks for later use. Hydrogen is blended with natural gas, and the blend is utilized for industrial and residential applications. The investigated system is modeled with the Aspen Plus software, and hydrogen production, blending, and combustion processes are analyzed accordingly. With the hydrogen addition up to 20% in the blend, the carbon dioxide emissions of combustion decrease from 14.7 kmol/h to 11.7 kmol/h, when the annual cost of natural gas is reduced from 9 billion $ to 8.3 billion $. The energy and exergy efficiencies for the combustion process are increased from 84% to 97% and from 62% to 72%, respectively by a 20% by volume hydrogen addition into natural gas.     

Hydrogen production via decomposition of hydrogen sulfide by synergy of non-thermal plasma and semiconductor catalysis

Direct H₂S decomposition induced by plasma with an aid of alumina-supported metal sulfide semiconductors (ZnS/Al₂O₃ and CdS/Al₂O₃) for the production of hydrogen was investigated in a dielectric barrier discharge (DBD) reactor. Effects of specific input energy (SIE), feed flow rate, metal sulfide loading, and added hydrogen on the performance of H₂S decomposition were studied. With the aids of ZnS/Al₂O₃ and CdS/Al₂O₃, full conversion was obtained at reasonably low energy costs. The 100-h test runs indicated that both ZnS/Al₂O₃ and CdS/Al₂O₃ were stable in the course of H₂S decomposition. A supported metal sulfide solid solution (Zn_0.4Cd_0.6S/Al₂O₃) exhibited higher performance than ZnS/Al₂O₃ and CdS/Al₂O₃, achieving full conversion at a reduced energy cost. The mechanism of the plasma-induced H₂S decomposition with an aid of a semiconductor catalyst was tentatively proposed.     

Cobalt sulfide modified graphitic carbon nitride semiconductor for solar hydrogen production

Mesoporous graphitic carbon nitride (mpg-CN) was modified with cobalt sulfide (CoS) by using an impregnation-sulfidation approach. The gas-phase sulfidation of CoS in nanoporous networks at certain temperature allows for the formation of intimate contact between the host carbon nitride and CoS nanoparticle, establishing noble-metal free heterojunctions for charge separation and collection at material interface. The resultant CoS/mpg-CN was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂-sorption, X-ray photoelectron spectroscopy (XPS), UV–Vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and electrochemical measurement. On the basis of the physicochemical and electrocatalytic characterization results of CoS/mpg-CN, it was revealed that CoS functioned as a cocatalyst to promote the migration of excited electron from mpg-CN toward CoS as well as to provide reactive sites for H₂ production at lower overpotentials. As a result, the rate of H₂ evolution over mpg-CN under visible light illumination (λ > 420 nm) was significantly improved after loading with CoS and the optimal loading amount of CoS was found to be 1.0 at. %.     

Hydrogen photoproduction from hydrogen sulfide on Bi2S3 catalyst

Films of polycrystalline Bi₂S₃ have been prepared onto bismuth and platinum substrates by electrodeposition from an aqueous sulfide bath. The films were thin, uniform and well adhered. Bi₂S₃ is a direct band gap semiconductor with a value of 1.28 eV optimally matched with the solar spectrum. The photoelectrochemical study was undertaken for the generation of hydrogen by using illuminated n-Bi₂S₃ particles; it was found that hydrogen evolution depends highly on the synthesis method of powder. Impregnation of platinum onto Bi₂S₃ shows a production enhancement of about 25%. The most active photocatalyst, prepared by a solvent thermal process and loaded with Pt in 0.1 M S²⁻ alkaline electrolyte, yields 2.13×10⁻² ml mg⁻¹ of H₂ after 4 h of irradiation with the visible output of a 500 W halogen lamp.     

Towards a hydrogen economy in Poland

The global changes in energy policy, including the increasing contribution of renewable sources of energy to the total output of produced energy and various attempts to introduce advanced energy technologies, and the increasingly efficient use of the energy that had already been emitted are sufficient reasons to discuss Poland's energy policy. The present work features an analysis of the current state of Poland's energy economy and the economic factors that affect the power industry. The tenets of Poland's current energy policy are also presented in the context of hydrogen energy. The possibilities and limitations concerning the transition to hydrogen power in Poland are discussed taking into account a number of aspects, some of which include the degree of development of the electric power infrastructure, the current and future demand for electric energy with regard to the current geopolitical and economic situation of Poland, and Poland's membership in the European Union.     

Towards a sustainable hydrogen economy: Hydrogen pathways and infrastructure

Results from the European HySociety project (2003–2005) are revealed in which political, societal and technical challenges for developing a European hydrogen economy have been addressed. The focus is placed on the assessments of hydrogen pathways and infrastructure. It will show that no chain can be selected as an obvious winner according to primary energy demand, emission and cost. In order to ensure that the pathway losses are compensated by the more efficient end-use of the H₂ fuel, calculations based on well-to-tank losses and tank-to-wheel efficiencies are used. Furthermore, in order to look into the consequences of introducing hydrogen, a top-down scenario has been worked out. The message is that certainly the hydrogen distribution part for the transport application has to be improved to avoid loosing the emission gain that is obtainable, especially via carbon capture and storage of the CO₂. In order to quantify the market development a bottom-up approach has been established in particular for the transport sector.     

Challenges towards hydrogen economy in China

The increasingly serious energy crisis and environmental pollution caused by the excessive use of fossil fuels have been prompting China to aggressively seek a clean and self-sufficient energy source in the future. In the past decades, hydrogen has emerged as a promising alternative due to its advantages of cleanliness, abundance, high energy density, and high conversion efficiency. However, several challenges have to be overcome for China's successful transition to hydrogen economy. In this paper, the hydrogen supply chain is firstly described to help the readers to clearly understand the hydrogen economy. Subsequently, the feasibility of hydrogen economy is discussed by reviewing viewpoints from the literature. Finally, the challenges of China's transition to hydrogen economy are detailed summarized and discussed, and the strategies for China to develop hydrogen economy were compared with that of Japan and Australia.     

Hydrogen station evolution towards a poly-generation energy system

The present paper analyzes an innovative energy system based on a hydrogen station, as the core of a smart energy production center, where the produced hydrogen is then used in different hydrogen technologies adopted and installed nearby the station. A case study analysis has been proposed and then investigated, with a station capacity of up to 360 kg of hydrogen daily generated, located close to a University Campus. A hydrogen mobility network has been included, composed of a fuel cell hydrogen fleet of 41 vehicles, 43 bicycles, and 28 fuel cell forklifts. The innovative proposed energy system needs to meet also a power and heat demand for a student housing 5400 m² building of the University Campus. The performance of the system is presented and investigated, including technical and economic analyses, proposing a hydrogen refueling station as an innovative alternative fuel infrastructure, called Multi-modular Hydrogen Energy Station, marking its great potential in future energy scenarios.     

Hydrogen sulfide removal from biogas by biotrickling filter inoculated with Halothiobacillus neapolitanus

Hydrogen sulfide (H₂S), a highly corrosive gas, is found in biogas due to the biodegradation of proteins and other sulfur containing organic compounds present in feed stock during anaerobic digestion. The presence of H₂S is one of the biggest factors limiting the use of biogas. It should be removed prior to application of biogas in an electric generator or industrial boiler. The present research evaluated the performance of biotrickling filter inoculated with Halothiobacillus neapolitanus NTV01 (HTN) on the H₂S removal from synthetic biogas. HTN, isolated and purified from activated sludge, is a sulfur oxidizing bacteria able to degrade H₂S and thiosulfate to elemental sulfur and sulfate, respectively. Operational parameters in a short term operation were varied as following; gas flow rate (0.5–0.75 LPM); EBRT (40–120 s); the inlet H₂S concentrations (0–1500 ppmv); liquid recirculation rate (3.6–4.8 L/h). EBRT showed a greater effect to the removal efficiency than increasing H₂S concentration. Longer EBRT resulted higher removal efficiency. The changes of liquid recirculation rates did not significantly affect the removal efficiency. In long term operation, the gas flow rate and liquid recirculation rate were fixed at 0.5 LPM (120 s EBRT) and 3.6 L/h; and H₂S concentrations were varied (0–2040 ppmv). The maximum elimination capacity was found as 78.57 g H₂S/m³ h, which had greater performance than the previous studies.     

Hydrogen trapping: Synergetic effects of inorganic additives with cobalt sulfide absorbers and reactivity of cobalt polysulfide

The biphasic product CoS₂ + Co(OH)₂ obtained by oxidation of cobalt sulfide is known to trap hydrogen at room temperature and low pressure according to a balanced reduction equation. Adding various inorganic compounds to this original absorber induces their reduction by hydrogen in the same conditions at a significant rate: (i) excess cobalt hydroxide is reduced to metallic cobalt; (ii) nitrate ions are reduced to ammonia; (iii) sulfur and sodium thiosulfate are reduced to H₂S or NaHS and Na₂S, respectively. Without a hydrogen absorber these inorganic compounds are not reduced by H₂, suggesting synergetic effects involving H₂ and the hydrogen absorber. Amorphous cobalt polysulfide, CoS₅, is also reduced by hydrogen at room temperature and releases H₂S gas. In the presence of a base to neutralize H₂S gas, the reaction rate is initially slower than with the CoS₂ + Co(OH)₂ mixture due to the higher stability of polysulfide chains but the H₂ trapping yield is improved, making CoS₅ a good candidate for H₂ trapping.     

Enhancing the photocatalytic hydrogen evolution of copper doped zinc sulfide nanoballs through surfactants modification

In this study, copper-doped zinc sulfide nanoballs were successfully synthesized in DI water and ethanol solvent by a sonochemical approach using surfactants in aqueous medium, such as citric acid (CIT), sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPBr), polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP), and polyvinyl butyral (PVB). Since surfactants are usually organic compounds that are amphiphilic molecules and surface-active agents with unique properties stemming from their exclusive structure with a hydrophobic tail and hydrophilic head, they can self-organize to form colloidal aggregates of different morphologies. TEM images show that copper doped ZnS crystallites without surfactant have a hollow-sphere-like self-assembled nanostructure. When 2.0Cu/ZnS was prepared with CTAB surfactant, it had a flower-like microspheres. The other surfactants would make copper-doped zinc sulfide exhibit the nanospheric structure. The surfactant plays an important role on the transfer of photogenerated electrons and holes and prevents non-radiative recombination of electrons and holes at surface sites. Therefore, surfactants could significantly improve the photocatalytic activity. Hydrogen evolution from an aqueous solution containing 0.1 M Na₂S at pH 3 and 0.15 g L⁻¹ of 2.0Cu/ZnS photocatalyst with PVB surfactant had the maximum of 1137.5 μmol h⁻¹ g⁻¹.