Thermal decomposition behavior and kinetic analysis of microalgae from Lake Van (Türkiye): implications for biochar production

Abstract

In this study, microalgae isolated from the extreme environmental conditions of Lake Van (T & uuml;rkiye) 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 degrees 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 (Delta H) ranged from 241.26 to 395.93 kJ mol(-)1, the Gibbs free energy change (Delta G) ranged from 137.74 to 151.61 kJ mol(-)1, and the entropy change (Delta S) 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.