Characterization and Kinetic Study of Agricultural Biomass Orange Peel Waste Combustion Using TGA Data

This study presents a comprehensive kinetic and thermodynamic investigation of dried orange peel (OP) combustion, employing thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) at high heating rates (20-80 K min^-1). This gap in high heating rate analysis motivates the novelty of present study, by investigating OP combustion at 20, 40, 60, and 80 K min^-1 using TGA, to closely simulate rapid thermal conditions typical of industrial combustion processes. Thermal decomposition occurred in three distinct stages corresponding sequentially to the dehydration, degradation of hemicellulose, cellulose, and lignin. Activation energy (<i>E_a</i>) was calculated using six model-free methods-Friedman (FR), Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink (STK), Kissinger (K), and Vyazovkin (VY)-yielding values between 64 and 309 kJ mol^-1. The <i>E_a</i> increased progressively from the initial to final degradation stages, reflecting the thermal stability differences among biomass constituents. Further kinetic analysis using the Coats-Redfern (CR) model-fitting method identified that first-order (F1), second-order (F2), and diffusion-based mechanisms (D1, D2, D3) effectively describe OP combustion. Calculated thermodynamic parameters-including enthalpy (ΔH), Gibbs free energy (ΔG), and entropy (ΔS)-indicated the endothermic and increasingly non-spontaneous nature of the reactions at higher conversions. These findings demonstrate the potential of OP, an abundant agricultural waste product, as a viable bioenergy resource, contributing valuable insights into sustainable combustion processes.