Thermochemical behavior and kinetics study of algae pyrolysis using iron oxide catalyst

The shift in emphasis from fossil fuel-derived energy to waste-to-energy technologies has widened the possibility for environmentally sustainable methods such as pyrolysis. Algae collected from local sources that grow in wastewater using atmospheric CO₂ is a potential feedstock for pyrolysis. Thus, the work focuses on studying the pyrolysis reaction of macroalgae sourced from regional sources in the presence of Fe₂O₃ catalyst using the thermogravimetric analysis, followed by kinetic analysis using iso-conversional methods of Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink methods, and model free Kissinger method. The kinetic model was developed using master plot method. XRD analysis of the Fe₂O₃ catalyst confirms the presence of the maghemite and hematite phases in the sample. Based on the conversion profile, DTG trend, and kinetic parameter variation, the overall pyrolysis process can be divided into three different stages of dissociation reactions. The apparent activation energy calculated from different models varies in the range: stage I (∼268 kJ/mol), stage II (∼261 kJ/mol), and stage III (∼328 kJ/mol), respectively. Master plot analysis of the kinetic data confirms the best fit of the nucleation model (A2) to experimental data in stage II. Further, the thermodynamic properties of the reaction, such as change in enthalpy (ΔH), change in Gibbs free energy (ΔG), and change in entropy (ΔS) range between 206 and 405 kJ/mol, 189 and 651 kJ/mol, −450 and 27 J/mol/K, respectively, corroborates the complexity of the reaction. Kinetics and thermodynamic property analysis of complex reactions like pyrolysis is essential for pilot plant design.