Pirólise de resíduos torrefados de castanha-do-brasil: impactos no comportamento térmico e cinético

Abstract

The residues of Brazil nuts (Bertholletia excelsa) were evaluated, in their natural state and in torrefied form, for their energy potential during pyrolysis. Samples of shells (CBC) and husks (CBO) were torrefied at 220, 260 and 300 ºC for 30 and 60 min, and were characterized for their chemical and energetic composition. The evolution of gases was also observed during pyrolysis in a thermogravimetric analyzer coupled to a mass spectrometer (TGA/MS). In addition, the kinetics of the pyrolysis of untorrefied and torrefied samples were evaluated using the Flynn-Wall-Ozawa (FWO) and Vyazovkin (VYZ) models. The predominant reaction mechanism was determined by Master-plot method. The mean value of the activation energies ranged from 132.24 to 134.95 kJ mol-1 for CBC, from 135.53 to 138.47 kJ mol-1 for CT263, from 149.10 to 150.96 kJ mol-1 for CBO and from 145.83 to 148.14 kJ mol-1 for OT263. It was found that D2 and D4 diffusion mechanisms are prevalent in the decomposition of untorrefied samples, while torrefied samples were better adjusted to the F1/A2/A3/A4 nucleation models. As a whole, in view of the optimized parameters and elevation of the thermal stability of the material, the results demonstrate good potential for the use of Brazil nut shells and husks torrefied at 260 ºC for 30 min as biochar, whose mass yield after torrefaction was 77 and 69.2%, respectively. In addition, pyrolyzed Brazil nut residues also have great potential in the production of bio-oil and biogas, considering the large amount of volatile material in their composition.