Thermal-oxidation study of biodiesel by proton nuclear magnetic Resonance (1H NMR)

Abstract Biodiesel is a renewable biofuel suitable for diesel replacement. Biodiesel has in its composition unsaturated fatty esters making it easily degraded. The objective of the present work was to investigate biodiesel thermal-oxidation by 1H NMR spectroscopy. Using the NMR was possible to analyze the signal intensities of the olefinic, bis-allylic and allylic protons of the chemical bonds, obtain the oleic, linoleic, linolenic and saturated acyl groups proportions, observe and classify some oxidation products. Two sets of biodiesel were analyzed, the first was oxidize in the Rancimat equipment at 110 °C during 8 h, and the second was oxidized in an oven at 50 °C during 17 days. The biodiesel oxidized at 110 °C had a more expressive degradation when compared to the samples oxidized at 50 °C. The samples presented an increase in the saturated proportion. It was possible to observe the formation of oxidation products as hydroperoxides and aldehydes as propanal and 2-propenal.