Waste to H 2 Sustainable Processes: A Review on H 2 S 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 H 2 S 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 H 2 S conversion is well-established through the Claus process, novel technologies for H 2 S 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 (H 2 SMR), non-thermal plasma, photocatalytic decomposition, decomposition through cycles and electrolysis are analyzed for the H 2 production from H 2 S. They represent promising alternatives for the simultaneous H 2 S valorization and H 2 production, without direct CO 2 emissions, as opposite to the traditional methane steam reforming. The various H 2 S 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 H 2 SMR 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.