Kinetic and thermodynamics study of the pyrolytic process of the freshwater macroalga,Chara vulgaris

This is the first study where the pyrolysis of the freshwater macroalga Chara vulgaris was explored to reveal its bioenergy potential. The suitability of C. vulgaris to bioenergy conversion via pyrolysis was accessed in terms of kinetic triplet and thermodynamic parameters. For this purpose, pyrolysis experiments under a thermogravimetric scale were conducted at multiple heating rates (5, 10, and 20 °C min^?1) in an inert atmosphere. The mass-loss profiles of C. vulgaris pyrolysis showed that there are two dominant decomposition stages that are related to distinct chemical components inside its structure and that directly affect the calculated kinetic triplet and thermodynamics parameters. The average activation energy obtained using isoconversional methods of Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Friedman was in the range of 52.87–72.91 kJ mol^?1 for the first decomposition stage and 156.14–174.65 kJ mol^?1 for the second decomposition stage. The pyrolytic conversion of C. vulgaris initially follows a second-order reaction model (first decomposition stage), while in second decomposition stage is controlled by a second-order Avrami-Erofeev reaction model. The kinetic results derived from the non-isothermal decomposition of C. vulgaris proved its suitable characteristics for pyrolysis. Additionally, multi-stage kinetic interpretation was successfully attained based on two kinetic triplets, where reconstructed pyrolysis behavior correlated well with experimental pyrolysis behavior. The changes in enthalpy, Gibbs free energy, and entropy for first decomposition stage were 67.58±0.25 kJ mol^?1, 180.77±5.30 kJ mol^?1, and ?176.65±0.41 J mol^?1 K^?1, and for the second decomposition stage the values were 166.70±0.09 kJ mol^?1, 285.51±1.29 kJ mol^?1, and ?124.29±0.09 J mol^?1 K^?1, respectively. Based on thermodynamic aspects, C. vulgaris is particularly interesting for use as a raw material to produce biofuels and bioenergy.