Evaluating the bioenergy potential of cupuassu shell through pyrolysis kinetics, thermodynamic parameters of activation, and evolved gas analysis with TG/FTIR technique

Abstract

This research aimed to investigate the physicochemical properties and the pyrolysis performance of cupuassu shell (Theobroma grandiflorum) under a thermogravimetric scale. The pyrolysis experiments were carried out using a pure nitrogen atmosphere and at five heating rates (5, 10, 20, 30, and 40 K min−1). The pyrolysis kinetic triplet was calculated from the DTG thermograms using the isoconversional methods of Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink combined with the compensation effect and master plots methods. TGA analyses revealed that cupuassu shell pyrolysis follows a devolatilization process of two steps: (1) represented by the two-dimensional diffusion-reaction model (D2), with average activation energies within 102.9–107.5 kJ mol−1, and (2) represented by the fourth-order reaction model (F4) with average activation energies within 176.7–243.0 kJ mol−1. Still, the pre-exponential factor value for the first kinetic stage (1.64×108 min−1) was lower than that of the second kinetic stage (3.19×1010 min−1). As verified, the kinetic triplets efficiently derived the global kinetic expression of cupuassu shell pyrolysis, reproducing reliable data on conversion rates. The evaluation of thermodynamic parameters of activation showed that cupuassu shell is viable biomass for pyrolysis applications, with values of ΔH≠ > 0, ΔG≠ > 0, and ΔS≠ < 0. The TGA-FTIR analysis showed that the evolved pyrolysis products were dominated by alcohols, aldehydes, ketones, organic acids, and aromatic/aliphatic hydrocarbons, supporting the utility of cupuassu shell as a potential source for bio-based chemicals production. In summary, the insights of this study validate the cupuassu shell as a prospective feedstock for producing bioenergy and bio-based chemicals, also bringing useful information for engineering purposes in the design or simulation of large-scale pyrolysis reactors.