Effect of extractive removal and heating rates on pequi seed torrefaction: A detailed kinetic and predictive study for biofuel production

This study uniquely applied the two-step reaction model to predict kinetics, solid yield (SY), and biocoal properties for valorizing raw (PS) and de-oiled (PSWE) pequi (Caryocar brasiliense) seed residues via torrefaction. It highlights the impact of extractives on kinetic behavior and biocoal properties, establishing an optimal biofuel valorization pathway. Torrefaction experiments were conducted at 200–300 °C, holding times of 20–60 min, and heating rates of 7–15 °C min−1. Thermogravimetric analysis (TGA) revealed distinct thermal behaviors between PS and PSWE, particularly at 225–250 °C, linked to the decomposition of unsaturated fatty acids and carotenoids. Extractive removal influenced SY during light torrefaction but not under severe conditions, enabling chemical valorization without yield loss. The model predicted torrefaction outcomes with high accuracy (R2 = 0.97–0.98). Predicted HHVs and energy yields ranged from 22.89 to 24.70 MJ kg−1 and 85.8–48.81 % (PS) and 18.84–22.79 MJ kg−1 and 96.54–54.84 % (PSWE). Sobol sensitivity analysis identified temperature as the most influential factor (45.84–50.04 %), followed by holding time (25.8–33.57 %), with minimal heating rate impact (<2.6 %). Integrating circular economy principles, this work underscores the dual valorization of biomass as biofuel and extractives as potential biorefinery feedstock, aligning with SDGs 7 (Clean Energy) and 13 (Climate Action).