Hydrogen production from solar thermal dissociation of methane in a high-temperature fluid-wall chemical reactor

This study addresses the exploration of an unconventional route for potentially cost effective hydrogen production with solar thermal energy. The process co-produces hydrogen-rich gas and high-grade Carbon Black (CB) from concentrated solar energy and methane. The approach is based on a single-step thermal decomposition (pyrolysis) of methane to hydrogen and CB, without catalysts and without emitting carbon dioxide since solid carbon is sequestered as carbon black. A high temperature nozzle-type solar chemical reactor has been developed in which the solar radiation absorbed by a graphite nozzle is transferred to the flow of reactant (fluid-wall reactor). The conversion of methane dissociation depends strongly on the solar power input, on the geometry of the graphite nozzle, and on the inert and reactive gas flow rates, which determine both the residence time and the inlet CH4 mole fraction. Maximum chemical conversion of methane was up to 99% (yield of hydrogen up to 90%). It was obtained with a vertical-axis solar furnace (2 m-diameter concentrator), with a given geometry of the nozzle determining the fluid-wall reaction surface area, and with the lowest flow rate of methane investigated (0.1 Ln/min). For each target tested, the higher the inlet flow rate of methane or argon, the lower the gas residence time, thus the lower the chemical conversion.