Thermal Conversion Pathways of Chontaduro (Bactris gasipaes Kunth) Rachis: Kinetic, Evolved- Gas, and Operational Assessment for Carbon-Enriched Products

Abstract Chontaduro ( Bactris gasipaes Kunth) rachis is an underutilized agro-industrial residue with potential as a lignocellulosic feedstock for thermochemical conversion and biorefinery applications. This study investigated its thermal conversion behavior by integrating multi-rate thermogravimetric and derivative thermogravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC), evolved-gas mass spectrometry (EGA-MS), and isoconversional kinetic modeling. Thermal decomposition proceeded through three main regimes: dehydration between 25 and 150°C, active devolatilization from approximately 162 to 277°C, and progressive carbonization up to 700°C. The active devolatilization stage accounted for nearly 35–37% mass loss and was associated with the synchronized evolution of CO₂, H₂O, and NH₃-related fragments near the principal DTG maximum. Flynn–Wall–Ozawa and Friedman analyses revealed conversion-dependent activation energies, indicating a transition from labile carbohydrate-rich structures to more recalcitrant cellulose- and lignin-derived domains. Differential master plots identified an Avrami–Erofeev-type behavior as the best apparent descriptor of the devolatilization stage, while thermal-shift factors confirmed that heating rate effects were conversion-dependent rather than uniform. The conversion–temperature map further enabled the identification of mild, torrefaction-like, and advanced carbonization windows for producing partially devolatilized or carbon-enriched solid products. Overall, this work provides a biorefinery-oriented framework linking feedstock composition, volatile evolution, kinetic barriers, and operational thermal-severity selection for the valorization of chontaduro rachis.