## 2 Results and Discussion
### Physicochemical Characterization of the Residual Babassu oil and Free Fatty Acids
In this study, the oxidative stability of the babassu residual oil was 1.30 h, which is much lower than that found by [PERSON] et al., (2019) [55], which was 33.69 h. This is due to the fact that the raw material used in this study is a residual oil, favoring the activity of oxidizing agents. Kinematic viscosity is related to the length of the carbon chain and the degree of saturation of the fatty acids present in oils and fats [63]. Saturated fatty acids have a linear conformation, allowing a more effective interaction between molecules, while unsaturated fatty acids present folds in the carbon chain for each double bond, causing molecular interactions with low efficiency and reducing their kinematic viscosity [68]. It is possible to observe that the value of the kinematic viscosity of the residual oil (3.96 mm\({}^{2}\)/s) is greater than that of the fatty acids produced (7.78 mm\({}^{2}\)/s), this fact may be \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Analytical Parameter** & \begin{tabular}{c} **Technical** \\ **Norm** \\ \end{tabular} & \begin{tabular}{c} **Residual** \\ **Babassu Oil** \\ \end{tabular} & \begin{tabular}{c} **Babassu Oil** \\ \end{tabular} & \begin{tabular}{c} **Soy Oil** \\ \end{tabular} & \begin{tabular}{c} **CODEX** \\ \end{tabular} \\ \hline \multirow{2}{*}{Acidity Level (mgKOH/g)} & [PERSON] & 4.851  & - & 0.41 & 0.28 & 0.50 \\ \hline \multirow{2}{*}{\begin{tabular}{c} Saponification Index \\ (mgKOH/g) \\ \end{tabular} } & [PERSON] & \multirow{2}{*}{271.94} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{245-256} \\  & Institute [59] & & & & & \\ \hline \multirow{2}{*}{\begin{tabular}{c} Oxidative Stability \\ (hours) \\ \end{tabular} } & EN 14.214 & \multirow{2}{*}{1.30} & \multirow{2}{*}{-} & \multirow{2}{*}{-} & \multirow{2}{*}{7.16} & \multirow{2}{*}{-} \\  & [60] & & & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Kinematic Viscosity at 40 \({}^{\circ}\)C \\ (mm\({}^{2}\)/s) \\ \end{tabular} } & ASTM & 3.96 & \multirow{2}{*}{2.95} & \multirow{2}{*}{3.18} & \multirow{2}{*}{3.15} & \multirow{2}{*}{1.44–1.45} \\  & D445-18 [61] & & & & & \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Density at 20 \({}^{\circ}\)C \\ (g/cm\({}^{2}\)) \\ \end{tabular} } & NBR 14.065 & \multirow{2}{*}{0.92} & \multirow{2}{*}{0.92} & \multirow{2}{*}{0.92} & \multirow{2}{*}{0.92} & \multirow{2}{*}{0.914–0.917} \\  & [62] & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of the physicochemical characterization of residual babassu oil. linked to the quality of the raw material since it had both saturated and unsaturated fatty acids, in addition to oxidizing agents favoring their degradation. After the saponification reaction followed by acid hydrolysis, it was possible to obtain saturated fatty acids, increasing the kinematic viscosity [68]. Both results showed high values compared to literature, shown in Table 3.  
The density values obtained were (0.92 g/cm\({}^{3}\)) for the residual babassu oil and (0.87 g/cm\({}^{3}\)) for the free fatty acids. Density is a measure used in the characterization of oils and fats in the liquid state and that varies inversely with the average molecular weight of fatty acids or with temperature and directly with the degree of unsaturation [69]. As the fatty acids obtained were mostly saturated, their value was lower, compared to the residual oil, which was also composed of unsaturated fatty acids [70]. The values of the physicochemical properties of residual babassu oil and free fatty acids are very close to the oils studied in the literature by [PERSON] et al. (2019) [58] and [PERSON] (2013) [57] (Table 3), so that babassu residual oil could be further explored as a raw material in the production of biodiesel.