Pyrolysis of cocoa shell and its bioenergy potential: evaluating the kinetic triplet, thermodynamic parameters, and evolved gas analysis using TGA-FTIR

Abstract

This study presents the first attempt to focus on the cocoa shell pyrolysis in terms of kinetic triplet, thermodynamic parameters, and evolved volatile analysis using the TGA-FTIR technique. For reliable interpretation of the multistep pyrolysis of cocoa shell, the multiple kinetic triplets were adequately estimated by a combined kinetic procedure using five independent parallel reactions with the Vyazovkin isoconversional method, the compensation effect, and the master plot method. According to the results, the multiple kinetic triplets were able to describe the pyrolysis behavior of the cocoa shell with an accuracy of R2 > 0.9446 and the pyrolysis mechanisms exhibited different reaction models (n-order and contracting cylinder). Evolved volatile analysis suggested the presence of high-energy compounds (aromatic) and useful chemicals (aldehyde, ketone, esters, ether, and alcohols). The pre-exponential factors for the five pseudo-components of cocoa shell pyrolysis ranged from 2.56 × 1011 to 8.66 × 1016 min−1 (derived from the compensation effect method), while the values of Ea ranged from 99 to 271 kJ mol−1. From a comparative analysis, it was found that the results from the compensation effect method ensured the overall kinetic expression to be consistent with the experimental cocoa shell pyrolysis behavior. In contrast, the overall kinetic expression using pre-exponential factors derived from Kissinger’s method failed to match the experimental curves. The pyrolytic conversion of cocoa shell into bioenergy appeared as potentially viable (Ea – ΔH ≤ 5.5 kJ mol−1). The promising findings on the cocoa shell pyrolysis can expand the use of this residue in bioenergy applications, consisting of a great attempt toward its valorization.