Advances in molten media technologies for methane pyrolysis

Methane pyrolysis in molten media appears as a promising alternative to allow industrial scale-up of turquoise hydrogen production. The operation in a bubble column solves the main drawbacks of gas-phase traditional processes such as low heat transfer, reactor clogging and catalyst deactivation due to carbon deposition. High thermal conductivity and high density of molten media are the key features which make the achievement of high temperatures easy and the continuous separation of carbon feasible. The use of molten media enables the possibility to catalyze the process in continuous long-term operation. However, R&D efforts are still needed to ease the scale-up of the process, which actually is realized only at lab-scale. Issues include the optimization of hydrodynamic parameters such as bubble dimensions and bubble residence time, fundamental to maximize the process efficiency and the desired product, i.e., H2, yield. In this chapter, a deep review of the methane pyrolysis in molten media is conducted with the aim of evaluating the influence of hydrodynamic parameters and types of molten media used for methane conversion. Molten media are classified into three groups according to their chemical nature (metals, alloys and salts). The morphology and purity of the produced carbon is also discussed. Metals and alloys appear more active in methane decomposition already at low temperature, but they produce carbon highly contaminated by metals. On the contrary, molten salts have poor activity but guarantee the production of high purity carbon thanks to their solubility in water which enables easy removal of salt contaminations through water scrubbers.