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Up to 80% of hydrogen production is currently carried out through CO2 emission-intensive natural gas reforming and coal gasification. Water-splitting electrolysis using renewable energy (green H2) is the only process that does not emit greenhouses gases, but it is a quite energy-demanding process. To significantly contribute to the clean energy transition, it is critical that low-carbon hydrogen production routes that can replace current production methods and can expand production capacity to meet new demands are developed. A new path, alternative to steam reforming coupled with CCS (blue H2) that is based on methane cracking, in which H2 production is associated with solid carbon instead of CO2 (turquoise H2), has received increasing attention recent years. The reaction takes place inside the liquid bath, a molten metal reactor. The aim of this article is to model the main kinetic mechanisms involved in the methane cracking reaction with molten metals. The model developed was validated using experimental data produced by the University of La Sapienza. Finally, such a model was used to scale up the reactor architecture.

Methane cracking is considered a bridge technology between gray and green hydrogen production processes. In this work an experimental study of methane cracking in molten tin is performed. The tests were conducted in a quartz reactor (i.d. = 1.5 cm, L = 20 cm) with capillary injection, varying temperature (950–1070 °C), inlet methane flow rate (30–60 mL·min –1) and tin height (0–20 cm). The influence of the residence time in the tin and in the headspace on methane conversion and on carbon morphology was investigated. The conversions obtained in tin and in the empty reactor were measured and compared with results of detailed kinetic simulations (CRECK). Furthermore, an expression of a global kinetic constant for methane conversion in tin was also derived. The highest conversion (65% at Q 0 = 30 mL·min –1 and t = 1070 °C) is obtained for homogeneous gas phase reaction due to the long residence time (70 s), the presence of tin leads to a sharp decrease of residence time (1 s), obtaining a conversion of 35% at 1070 °C, thus meaning that tin owns a role in the reaction. Carbon characterization (scanning electron microscopy, Raman) reported a change in carbon toward sheet-like structures and an increase of the carbon structural order in the presence of molten tin media.