Drastic changes in biomass char structure and reactivity upon contact with steam

An Australian cane trash biomass was pyrolysed by heating at a slow heating rate to 700-900 °C in an inert gas atmosphere. The chars were then gasified in situ with steam. Our results indicate that the gasification of char with steam, even only for 20 s when the char conversion was minimal, resulted in drastic reduction in the intrinsic reactivity of char with air at 400 °C. The decreases in the char reactivity were not mainly due to the possible volatilisation of inherent catalysts during gasification in steam. Instead, the FT-Raman spectroscopy of the chars showed that the gasification of char with steam resulted in drastic changes in char structure including the transformation of smaller ring systems (3-5 fused rings) to large ring systems (≥6 fused rings). It is believed that the intermediates of char-steam reactions, especially H, penetrated deep into the char matrix to induce the ring condensation reactions.