Biomass char gasification by H₂O, CO₂ and their mixture: Evolution of chemical, textural and structural properties of the chars

The present study aims to understand the phenomenology of char gasification by monitoring the chemical, structural and textural char characteristics through the gasification reaction. Chars from beech wood were gasified under 20%H₂O, 20%CO₂ and 20%H₂O + 20%CO₂ in N₂ at 900° C. The gasification reactions were stopped at 20%, 50% and 70% of char conversion. The char properties were analysed by different analytical techniques such as temperature programmed desorption coupled to mass spectrometry, Raman spectroscopy, Scanning Electron Microscopy, N₂ manometry and X-ray Fluorescence. These analyses provide valuable information on the unfolding of the gasification reactions with H₂O, CO₂ and their mixtures. In particular, it is noted that H₂O and CO₂ gasification reactions follow different pathways. Moreover, during mixed atmosphere, despite that the char reactivity can be fairly expressed by summing the two individual reactivities, this apparent additivity appears to be the result of several competitions and synergies between H₂O and CO₂ reactions. - Highlights: • The char reactivity in gas mixture can be fairly represented by an additive law. • Structure, texture and surface chemistry of chars change during gasification. • H₂O and CO₂ gasification mechanisms are different. • The apparant additivity is the result of several inhibition and synergy interactions.