Thermal decomposition behavior and kinetic analysis of microalgae from Lake Van (Türkiye): implications for biochar production
摘要
In this study, microalgae isolated from the extreme environmental conditions of Lake Van (Türkiye) which is characterized by high salinity and alkalinity, were cultivated, characterized and pyrolytic behavior, kinetic and thermodynamic properties were investigated for biochar production. Thermogravimetric analysis was performed under a nitrogen atmosphere at heating rates of 10, 20 and 40 °C min⁻1. Activation energy values were calculated using the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Starink and Friedman isoconversional methods. The average activation energy values were determined to be 328.61, 321.96, 328.75, and 335.48 kJ mol⁻1 for the KAS, FWO, Starink and Friedman methods. According to the thermodynamic analysis results, the enthalpy change (ΔH) ranged from 241.26 to 395.93 kJ mol⁻1, the Gibbs free energy change (ΔG) ranged from 137.74 to 151.61 kJ mol⁻1, and the entropy change (ΔS) ranged from 0.14 to 0.49 J mol⁻1 K⁻1. The pre-exponential factor (A) values (1020–1039 min⁻1) were significantly higher than those typical of simple reactions, suggesting that the pyrolysis process involves complex, multi-step reaction mechanisms. Furthermore, the increase in the carbon content of the biochar from 50.30 to 74.64% and the decrease in the O/C atomic ratio from 0.58 to 0.06 indicated an increase in the degree of carbonization and the development of an aromatic structure. FTIR analysis also demonstrated that oxygen-containing functional groups decreased after pyrolysis and more stable aromatic structures formed. These results revealed that microalgae isolated from Lake Van possesses high thermal stability and is a suitable precursor material for biochar production.