Advanced characterization of oxidized derivatives in alternative fatty esters mixture for biodiesel purposes

Biofuels from unconventional sources contribute to the reduction of environmental impacts without competing with the food market. Samples of fatty esters mixture (FEM) for biodiesel purposes were produced from conventional and alternatives feedstocks sources of triacylglycerols (TAG). In this work, we evaluated the oxidative stability through a complex and advanced characterization at the molecular level of the chemical changes that occurred in these samples for a storage period of 2.5 years. Esters contents were determined by both TG and GC-FID analyses, and values with relative errors from 0.36 to 23.28% were obtained. Low molecular mass compounds derived from the oxidative processes and free fatty acids (FFA) contribute to these differences. TG curves also showed the presence of contaminants with high thermal stability, which were characterized by EASI(+)-MS. TAG and diacylglycerol (DAG) were identified, however, dimers and theirs derived from hydroperoxide degradation were detected as major contaminants, confirmed by the presence of biomarkers ions characteristics of dimers. Our work mapping and presenting the chemical profile of oxidative products of FEM, and in addition, we propose the correlation of relative abundance of ion m/z 349 corresponding to the hydroperoxide [C-18:2 + 2O + Na](+) with the peroxide index values.

Automated summary

This study evaluated the oxidative stability of fatty esters mixture (FEM) for biodiesel purposes and analyzed the chemical changes that occurred in these samples during a storage period of 2.5 years. The results showed differences in esters contents, which were influenced by low molecular mass compounds and free fatty acids (FFA). Contaminants with high thermal stability were also detected, and the relative abundance of ion m/z 349 was proposed as a correlation to the peroxide index values.