Investigation on thermal degradation properties of oleic acid and its methyl and ethyl esters through TG-FTIR

Thermogravimetric analysis in conjunction with Fourier transform infrared spectroscopy (TG-FTIR) is used to investigate thermal degradation properties of oleic acid and its esterification derivants of methyl ester and ethyl ester. Based on TG experimental results, which are operated under nitrogen atmosphere from 298 to 773 K at the sample temperature heated rates of 5, 10, and 15 K min−1, respectively, two degradation iso-conversional approaches of Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) are mentioned to calculate the apparent activation energy, based on which the apparent pre-exponential factor is obtained. Meanwhile, Avrami theory is used for the apparent reaction order estimation. Further, thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated to label the thermal degradation process directly. Also, the evolved gaseous products from TG are detected by FTIR online to understand the thermal degradation comprehensively. Information about fatty acid and its methyl ester and ethyl ester derived from TG-FTIR, especially the comparison between esterification derivants and their feedstock, has been rarely reported and is expected to contribute to the commercial application of biodiesel.