Uncovering Structure-Reactivity Relationships in Pyrolysis and Gasification of Biomass with Varying Severity of Torrefaction

The objective of this study is to establish the structure reactivity relationships in pyrolysis and gasification of biomass with varying severity of torrefaction. Pine was torrefied in a bench scale tubular reactor with varying torrefaction temperature (220-300 degrees C). The structural alterations in torrefied pine and its derived biochar were characterized by solid-state nuclear magnetic resonance spectroscopy (NMR) and Raman spectroscopy, respectively. The effect of torrefaction severity, as well as the resulting structural changes in pine, upon subsequent pyrolysis and gasification reactivity were systematically studied. The experimental results showed that the pyrolysis reactivity of pine was promoted by torrefaction, whereas the gasification reactivity of biochar derived from pine was reduced by torrefaction. The results were mainly attributed to the severe degradation, polycondensation, and carbonization of hemicellulose and lignin fractions during torrefaction of pine. The pyrolysis and gasification reactivity of torrefied pine was a strong linear function of its aromaticity or H/C molar ratio. Therefore, H/C molar ratio and aromaticity of pine were good indicators to quantitatively assess the structural alterations of pine during torrefaction and their impacts on the reactivity of subsequent pyrolysis and gasification. These findings provide a simple and efficient method to predict the pyrolysis and gasification reactivity of biomass with varying severity of torrefaction.