An assessment of carbon oxidation mechanism by dynamic oxidation/desorption in a Looping reactor

The mechanism of carbon oxidation by oxygen has been scrutinized by means of dynamic experiments consisting of cyclic oxidation of solid carbon at low-moderate temperature (200-300°C) followed by desorption of surface oxides at high temperature (700-800°C). The rapid shift between oxidation and desorption conditions is accomplished thanks to a purposely designed reactor consisting of a dual fluidized bed configuration equipped with a rapid transfer line that enables fast pneumatic conveying of the solid sample from one reactor to the other while keeping distinct reaction conditions in the two reactors. Results are analysed with a specific focus on the role and nature of surface oxides as intermediates in carbon gasification. The existence of surface oxides of different chemical nature and stability provides the starting point to elaborate a tentative mechanistic frame of the experiment. The key features of the phenomenology, namely the oxidation rate and the CO/CO2 ratio in the evolved gasification products, are interpreted in the light of the relative abundance and stability of "edge" oxides and epoxy moieties generated by carbon oxidation