This work explores the co-combustion behavior and oxidative degradation kinetics of high ash fraction loblolly pine (HAF-LP), kaolin clay (KC), and their binary mixtures (25:75, 50:50, 75:25) using thermogravimetric analysis (TGA) under a dynamic air environment. Heating rates of 5, 10, and 20 K/min and gas flow rates of 10, 20, and 30 mL/min were applied to investigate how thermal conditions and air exposure influence decomposition behavior. The aim is to better understand feedstock thermal variability, combustion behavior, and reactivity—critical parameters for conditioning, transport, and conversion reliability in biorefinery feedstock logistics. Compared to inert pyrolysis, the presence of oxygen introduced simultaneous combustion and devolatilization reactions. Pure HAF-LP exhibited three distinct degradation stages—hemicellulose, cellulose, and lignin—while KC followed a third-order (F3) dehydroxylation pathway. The blended samples showed overlapping thermal events, with increased KC content stabilizing decomposition and delaying ignition. TGA data revealed that increasing air flow rates accelerated burn-off, with faster ash point achievement for HAF-LP at 30 mL/min compared to 10 mL/min. DTG analysis showed peak shifts toward lower temperatures with higher air flow, indicating enhanced combustion kinetics. The sharpness and amplitude of DTG peaks increased at higher heating rates, especially for biomass-dominant blends, suggesting more aggressive volatile release and oxidation. DDTG profiles confirmed this, showing that higher flow rates and heat ramps led to faster and more complete burn-off, with steeper derivative slopes. Conversely, lower flow rates resulted in prolonged combustion, particularly in clay-rich mixtures. These behaviors were inverted compared to nitrogen runs, emphasizing oxygen’s catalytic effect on thermal degradation. Kinetic parameters were derived using Coats-Redfern (CR), Distributed Activation Energy Model (DAEM), and Friedman methods. While CR offered mechanistic insights across conversion zones, DAEM and Friedman revealed continuous activation energy profiles reflecting multi-stage oxidation and biomass-mineral interactions. This study provides a kinetic and thermal decomposition framework to predict and manage feedstock combustion variability in real-world systems. The findings directly support strategies for feedstock conditioning, reactor feeding reliability, equipment wear mitigation, and conversion predictability—ultimately improving the efficiency and consistency of biomass-to-energy operations in integrated biorefineries as well as promising applications in building materials.
