Pyrolysis Kinetics, Reaction Mechanisms, and Thermodynamic Analysis of Rice Husk via TGA–DSC Analysis for Biohydrogen Production Potential

ABSTRACT

Rice husk (RH) is one of the most abundant lignocellulosic agricultural residues with significant potential for thermochemical bioenergy conversion. In this study, the thermal degradation behavior, pyrolysis kinetics, reaction mechanism, and thermodynamic properties of RH collected from Fogera, Ethiopia, were investigated using integrated thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Pyrolysis experiments were conducted under nitrogen atmosphere at heating rates of 10, 20, and 30°C min ^{− 1} over a temperature range of 30°C–900°C. The TGA and DTG analyses revealed three major decomposition stages corresponding to moisture removal, active devolatilization of hemicellulose and cellulose, and lignin degradation with char formation. The maximum weight loss occurred during the active pyrolysis stage within 230°C–437°C, with peak decomposition temperatures shifting from 310°C to 345°C as the heating rate increased. The kinetic parameters were determined using iso‐conversional model‐free methods, namely Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO), together with the Coats–Redfern (CR) model‐fitting approach. The average activation energies obtained from KAS, FWO, and CR models were 80.51, 86.52, and 61.99 kJ mol ^{− 1} , respectively, indicating the favorable thermal reactivity of RH during pyrolysis. Thermodynamic analysis showed positive Gibbs free energy and enthalpy values, confirming that the decomposition process is energy‐dependent and thermally activated. The DSC analysis revealed both endothermic and exothermic thermal behaviors associated with multistage decomposition and volatile evolution during pyrolysis. However, the DSC results were interpreted only as indicators of thermochemical conversion behavior and not as direct confirmation of hydrogen evolution, since evolved gas compositions were not experimentally identified in this study. In a nutshell, the relatively low activation energy, significant volatile release, and favorable thermal decomposition characteristics suggest that rice husk is a promising feedstock for thermochemical bioenergy applications and hydrogen‐rich syngas production potential. The findings provide useful kinetic and thermodynamic data for reactor design, process optimization, and future advanced studies involving evolved‐gas analysis techniques such as TGA‐FTIR, TGA‐MS, and Py‐GC/MS.