Transformation of lignocellulosic biomass during torrefaction

In this study, the effect of torrefaction on the chemical and structural transformation of lignocellulosic biomass was investigated using complementary analytical tools. It was observed that the acid-insoluble fraction was increased from approximately 30 to 38% and the methoxyl content was decreased to about half after torrefaction at 330 °C for 2.5 min. These results highlight the formation of condensed structures along with lignin transformation via demethoxylation. Solid-state NMR spectroscopy indicated that upon torrefaction the aromaticity increased from about 36 to 60%. For the sample torrefied at 330 °C, the non-protonated aromatic carbon fraction was found to be about 60% of total aromatic carbons, indicating the formation of large aromatic clusters. The complementary analyses used in this study are proposed as a suitable approach for the elucidation of chemical and structural transformation of biomass during thermal treatment.

► Acid-insoluble residue increased to 38.2 from 30.1% in torrefied biomass at 330 °C.
► 51% of lignin modified via demethoxylation in torrefied biomass at 330 °C.
► Aromaticity increased from 35.8 to 59.6% in torrefied biomass at 330 °C.
► Non-protonated aromatic carbon fraction increased during torrefaction.