Hydrogen production from thermo-catalytic decomposition of methane using carbon black catalysts in an indirectly-irradiated tubular packed-bed solar reactor

Abstract

The solar thermo-catalytic decomposition of methane using carbon black catalysts for CO2-free hydrogen production is studied in a packed-bed reactor. The indirectly-irradiated reactor is based on a cavity receiver and a tube-type absorber in which a given load of particle catalyst is injected during on-sun operation, while enabling multiple refilling for catalyst replacement. Concentrated solar power is used as an external radiative source for supplying the high temperature process heat and for driving the endothermic reaction. The indirect irradiation via the intermediate opaque tubular absorber results in a more uniform heating of the whole reacting bed volume and thus an easier reaction temperature control and determination. Carbon particles are used for enhancing the rate of the heterogeneous decomposition reaction and the coupling of the reactor with a particle injection system is implemented to operate in semi-continuous mode with possibility of catalyst load renewal after deactivation.The packed-bed reactor was operated on-sun to investigate the effect of the various operating parameters on the reactor thermochemical performances. Complete methane conversion to hydrogen was achieved (100% selectivity to H2 with no side-products), but catalyst deactivation occurred progressively because of carbon deposition at the surface, with acetylene as the main evolving by-product. The temperature and the residence time of the flowing gas through the catalyst bed were identified as the main parameters influencing the chemical conversion and hydrogen yield. This type of scalable reactor configuration could be applied for continuous hydrogen production with in-situ catalyst regeneration or substitution without reactor operation break-down at high temperatures.