Unlocking the potential of pequi (Caryocar brasiliense) residues for bioenergy and renewable chemicals: Multicomponent kinetic modeling, thermodynamic parameter estimation, and characterization of volatile products through TGA and Py-GC/MS experiments

Abstract

The first study in the literature on the pyrolysis of pequi (Caryocar brasiliense) residues, focusing on the kinetic triplet, thermodynamic parameters, and characterization of volatile products utilizing TGA and Py−GC/MS techniques, is presented in this paper. Slow pyrolysis experiments were conducted on a thermogravimetric scale in a controlled atmosphere of pure nitrogen, with five distinct heating rates (5, 10, 20, 30 and 40 ºC min−1). The pyrolysis progress profiles were fitted using the Asym2Sig function to deconvolute the devolatilization rates of individual biomass pseudo-components, including extractives, hemicellulose, cellulose, and lignin. The average activation energies for pequi peel pyrolysis, as determined by the isoconversional methods of Friedman, Flynn−Wall−Ozawa, Kissinger−Akahira−Sunose and Starink, were higher (114.30 −319.13 kJ mol−1) than those estimated for pequi seeds (88.05 −168.39 kJ mol−1). The pre-exponential factors, obtained through the kinetic compensation effect method, exhibited a range of values between 3.6 × 1011 and 2.4 × 1030 min−1 for pequi peel and between 1.2 × 107 and 9.4 × 108 min−1 for pequi seeds. Utilizing the master-plots method revealed the involvement of F-type, A-type, and D-type reaction models in the pyrolysis of pequi residues. A slight difference between the Ea and ΔH values, less than 5 kJ mol−1, indicates the facile formation of reaction products during pyrolysis. The main organic volatile products obtained from the fast pyrolysis of pequi peel, as revealed by Py−GC/MS analysis, include furans, ketones, aldehydes, and ethers, constituting up to 52% of the total yield of the condensable fraction at 550 °C. Aliphatic hydrocarbons are the major organic volatile products derived from the fast pyrolysis of pequi seeds, accounting for approximately 74% of the total condensable fraction yield at 650 °C. This study provides new insights into the valorization of residues resulting from pequi fruit processing. As a result, a novel pathway for bioenergy and biobased chemical production via pyrolysis is established, aligning with the circular economy principle and capable of promoting energy matrix diversification.