Deepening the understanding and extending the potential of waste biomass temperature treatment using sunflower husk as an example

The efficient management of waste biomass, such as sunflower husk (SH), is vital for the currently desired shift towards Circular Economy and maximizing resource efficiency in various industrial sectors. Among the most popular approaches applied to biomass are thermal treatments aimed at energy production and the manufacturing of solid and liquid fuels. Therefore, torrefaction and pyrolysis of biomass, especially wood, have been comprehensively investigated in this context. Herein, the presented study focuses on slightly overlooked aspects critical for other potential applications, such as fertilizers, active fillers in composite systems, or food additives. Torrefaction temperatures lower than conventionally applied in the energy sector have been investigated, and the impact of temperature-induced non-enzymatic browning reactions, including Maillard reactions, as well as partial thermal decomposition and structural rearrangements on the appearance, chemical composition, morphology, grinding susceptibility, and thermal stability of SH has been analyzed. Proper selection of torrefaction parameters enabled adjustment of SH browning extent and covered the entire palette of brown colors. Appearance changes aligned with the moisture removal, hemicellulose degradation, and rearrangements in cellulose crystalline structures, increasing SH crystallinity and reducing atomic H/C and O/C ratios. Moreover, these structural changes gradually enhanced the grinding susceptibility of SH, which will facilitate its particle size reduction, crucial in multiple applications. Partial and controllable temperature-induced degradation also shifted the thermal decomposition onset by ∼50 °C, which significantly extends the potential processing window and opens up new directions for torrefied SH. Finally, tracking torrefaction energy consumption revealed satisfactory energy efficiency of the proposed process.