Waste to H₂ Sustainable Processes: A Review on H₂S Valorization Technologies

In the energy transition from fossil fuels to renewables, the tendency is to benefit from ultra-sour natural gas reserves, whose monetization was previously considered unviable. The increasing H2S content together with the growing concern about emissions that are harmful to the environment, make necessary the development of efficient strategies for pollutants management. Although large-scale H2S conversion is well-established through the Claus process, novel technologies for H2S valorization could be a reliable alternative for waste-to-valuable chemicals, following the circular economy. In this perspective, technologies such as Hydrogen Sulfide Methane Reformation (H2SMR), non-thermal plasma, photocatalytic decomposition, decomposition through cycles and electrolysis are analyzed for the H-2 production from H2S. They represent promising alternatives for the simultaneous H2S valorization and H-2 production, without direct CO2 emissions, as opposite to the traditional methane steam reforming. The various H2S conversion routes to H-2 are examined, highlighting the advantages and disadvantages of each of them. This review focuses in particular on the most promising technologies, the H2SMR and the non-thermal plasma, for which preliminary process scheme and techno-economic analysis are also reported. Finally, the major research gaps and future developments necessary to unlock the full potential of hydrogen sulfide valorization as a sustainable pathway for hydrogen production are discussed.