Valorização energética do caroço de açaí (Euterpe oleracea): caracterização físico-química e termodinâmica pós-torrefação úmida

Abstract

Excessive consumption of fossil fuels is depleting their reserves and intensifying greenhouse gas emissions, worsening global warming. The shift to renewable energy sources is crucial for a sustainable future. This study investigates the energy potential of açaí seeds, an abundant lignocellulosic biomass in the Amazon, in their natural form (CA-IN) and after hydrothermal pretreatment via wet torrefaction (HTCA) through pyrolysis and thermogravimetric analysis. The samples were torrefied at 160, 180, and 190°C for 1, 2, 4, and 6 hours, and characterized for their chemical and energy composition. Thermogravimetric analyses were performed to identify stages of thermal decomposition. Gas evolution was observed during pyrolysis in a thermogravimetric analyzer coupled with a mass spectrometer (TGA/MS). The Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) kinetic models determined the activation energy (Ea) between 154.27 and 177.65 kJ/mol-1 for the studied samples and the pre- exponential factor (A) between 1.96×1014 and 1.67×1017 s-1. These data indicated that wet torrefaction improves the thermal stability of the biomass. Thermodynamic parameters (enthalpy, entropy, and Gibbs free energy) were calculated, confirming the efficiency of the pyrolysis process. The predominant reaction mechanisms F2, D1, and D2 were determined by the master plot method, showing second-order reactions and one-dimensional and two-dimensional diffusion, suggesting the complexity of the pyrolysis process for this biomass. Overall, considering the optimized parameters and the increased thermal stability of the material, the results demonstrated great potential for the use of açaí seeds torrefied at 160°C for 2 hours, with a mass yield after torrefaction of 90.06%, as a promising source for biofuel production using Amazonian biomass.