Study of solid chemical evolution in torrefaction of different biomasses through solid-state 13C cross-polarization/magic angle spinning NMR (nuclear magnetic resonance) and TGA (thermogravimetric analysis)

The objective of this work is to compare mass loss and chemical evolution of the solid phase, versus time, during dynamic torrefaction of different types of biomass. For this purpose, two experiments, ThermoGravimetric Analysis and solid-state 13C Cross-Polarization/Magic Angle Spinning Nuclear Magnetic Resonance, were run on four representative biomasses. Overall mass loss and chemical evolution of the solid phase were followed, respectively, as a function of temperature and time. Thanks to this coupled information, it was shown that the knowledge of both solid mass loss and chemical evolution is necessary to characterize torrefaction severity. Moreover, biomasses containing higher proportions of xylan lost mass faster than those containing lower proportions. Lignin showed a protecting role towards cellulose, which would lead to a faster degradation of non-woody biomasses in comparison with woody biomasses. Three parameters would have an influence on solid chemical evolution during torrefaction: xylan content in hemicellulose, lignin content in biomass, and cellulose crystallinity.