Valorization of royal palm tree agroindustrial waste via pyrolysis with a focus on physicochemical properties, kinetic triplet, thermodynamic parameters, and volatile products

Abstract

This work reports experimental findings for pyrolysis of the royal palm tree (RPT) waste, particularly emphasizing the kinetic triplet, thermodynamic parameters, and characterization of volatile products. Pyrolysis experiments were conducted in a thermogravimetric analyzer and an analytical pyrolyzer coupled with a gas chromatography-mass spectrometry (Py–GC/MS). First, pyrolysis of RPT waste was considered to proceed in four independent devolatilization reactions linked to extractives, hemicellulose, cellulose, and lignin. The fractional contributions for these pseudo-components were determined as follows: 0.0600 for extractives, 0.3140 for hemicellulose, 0.2667 for cellulose, and 0.3196 for lignin. The following standard procedure for determining the kinetic triplet was adopted: four isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Starink), Kissinger's method, and integral master plots. The mean overall activation energy and the pre-exponential factor for the four independent devolatilization reactions are 78.3 kJ mol−1 and 9.5 × 107 min−1, 107.2 kJ mol−1 and 5.7 × 109 min−1, 130.6 kJ mol−1 and 7.0 × 1010 min−1, and 153.6 kJ mol−1 and 1.2 × 1013 min−1, respectively. The most suitable reaction models for the pyrolysis of RPT waste belong to the nucleation-growth and n-order reaction mechanisms. The resulting values of the thermodynamic parameters ΔH, ΔG, and ΔS were respectively within 71.8–144.3 kJ mol−1, 138.0–173.2 kJ mol−1, and −138.4–(−43.7) J mol−1 K−1. Numerical simulations were performed to verify the kinetic triplets' results in one overall pyrolysis rate expression. The simulated and experimental kinetic curves exhibited a strong agreement, indicating a high level of consistency between them. The findings from this work suggest the suitability of royal palm waste as a promising raw material for producing bioenergy and renewable chemicals, in addition to being valuable for designing large-scale pyrolyzers for this type of waste.