Characterization, Combustion Behaviour, and Kinetic and Thermodynamic Modelling of Mango Peel as a Potential Biomass Feedstock

Abstract

Mango peel (MP), an abundant agro-industrial residue, was evaluated as a solid biofuel using combined physicochemical characterisation and non-isothermal thermogravimetric kinetics (TGA). Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed hydroxyl-rich surfaces and porous microstructures. Thermogravimetric combustion, conducted at heating rates of 20–80 K min−1, displayed three distinct stages. These stages correspond to dehydration (330–460 K), hemicellulose/cellulose oxidation (420–590 K), and cellulose/lignin oxidation (540–710 K). Kinetic analysis using six model-free methods (Friedman (FR), Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Starink (STK), Kissinger (K), and Vyazovkin (VY)) yielded activation energies (Ea) of 52–197 kJ mol−1, increasing with conversion (mean Ea ≈ 111 kJ mol−1). Coats–Redfern (CR) fitting confirmed a three-dimensional diffusion mechanism (D3, R2 > 0.99). Thermodynamic analysis revealed that the formation of the activated complex is endothermic, with activation enthalpy (ΔH) values of 45–285 kJ mol−1. The process was found to be non-spontaneous under the studied conditions, with Gibbs free energy (ΔG) values ranging from 83 to 182 kJ mol−1. With a high heating value (HHV) of 21.9 MJ kg−1 and favourable combustion kinetics, MP is a promising supplementary fuel for industrial biomass boilers. However, its high potassium oxide (K2O) content requires dedicated ash management strategies to mitigate slagging risks, a key consideration for its practical, large-scale application.