Determination of Residual Oil in Biodiesel via Quasi-Isothermal Thermogravimetry (TGA-qISO) and Differential Scanning Calorimetry (DSC)

The present work aims to determine the levels of contaminant oils in biodiesel obtained from the residual oil of the industrial processing of Nile tilapia via Quasi-Isothermal Thermogravimetry (TGA-qISO) and Differential Scanning Calorimetry (DSC). For this purpose, mixtures of tilapia oil (OT) and biodiesel (BD) were prepared in the mass proportions of OT/BD (5:95 m/m), OT/BD (10:90 m/m), OT/BD (15:85 m/m), OT/BD (20:80 m/m), OT/BD (25:75 m/m) and OT/BD (30:70 m/m). These mixtures were used to construct the calibration curve of the TGA-qISO and DSC techniques. To evaluate the efficiency of these techniques, three samples were prepared at concentrations of 7.01 OT%, 16.66 OT% and 27.05 OT%. The data obtained show that the biodiesel/oil mixtures presented two stages of mass loss, the first between 100 and 200 °C, which was attributed to the decomposition of the biodiesel, and from 250 °C, to the decomposition of the oil. In the DSC curves of the mixtures, it was observed that as the concentration of tilapia oil in the mixtures increases, there is a decrease in the intensity of the peaks and a shift to a higher temperature range. Statistical tools show that the TGA-qISO measurements presented analytical curves with a correlation coefficient (r) of 0.9999, while in the DSC analyses, r of −0.9727 and −0.9903 were obtained. Analysis of variance (ANOVA) confirmed that there is no significant difference between the measurements performed by TGA-qISO and DSC. This result shows that both techniques can be used to determine the oil adulteration in biodiesel samples.