Kinetic and thermodynamic analysis of biodiesel and associated oil from Jatropha curcas L. during thermal degradation

Herein, Jatropha curcas seed oil, a non-edible plant oil, was employed as low-grade feedstock to make biodiesel via a two-step transesterification process. The Jatropha curcas oil (JCO) and its corresponding biodiesel (JCO-B) were characterized by FTIR and GC-FID analyses. Thermal stability experiments were conducted using thermogravimetry (TGA/DTG) technique at different heating rates of 5, 10 and 15 °C/min with a temperature range from 30 to 900 °C. Kinetic and thermodynamic characteristics of JCO and JCO-B were investigated. The TGA data were evaluated by the Flynn-Wall-Ozawa (FWO) and Vyazovkin kinetic models, and the reaction order was predicted by Avrami theory. The obtained JCO-B conformed to European standard EN 14103, while its FAME content was 97.51 wt.%. The TGA data fitted well to the FWO isoconversional model with average activation energies of 108.22 kJ mol⁻¹ and 33.91 kJ mol⁻¹ for JCO and JCO-B, respectively. Additionally, on average, reaction orders estimated by the Avrami model were 1.21 and 1.19 for JCO and JCO-B, respectively. Positive enthalpy change (∆H) and Gibbs-free energy (∆G) suggested an endothermic and nonspontaneous thermal degradation process, while the negative entropy change (∆S) indicated a more ordered process and reaffirmed nonspontaneous reaction. The findings from this study indicated that the TGA/DTG technique could be used to predict the thermal and oxidation stability of biodiesel with respect to time.