The evolution of the sunflower oil ethanolysis conversion with reaction
time at 50 °C and several NaOH concentrations within the 0.06–
0.30 wt.% range is shown in Fig. 2A and B for initial alcohol-to-oil
molar ratios of 6:1 and 12:1, respectively. As expected, for a given initial
concentration of the reactants, the oil conversion increases as the initial
NaOH concentration increases. As discussed in the previous section,
there is a great influence of the excess of ethanol utilized. In fact, at
the relatively low ethanol-to-oil molar ratio of 6:1, Fig. 2A shows that
the final oil conversions are between 69% and 98% for NaOH concentrations
of 0.06 and 0.3 wt.%, respectively. If the ethanol-to-oil molar ratio
increases to 12:1, it is possible to reach almost complete oil conversion
within 15 min with an initial NaOH concentration of 0.3 wt.%. These results
illustrate the importance of the excess of alcohol to preserve the
catalytically active ethoxide species during ethanolysis reactions catalyzed
by NaOH. This positive effect ismainly based on the shift of the hydroxide/
ethoxide equilibrium (Eq. (4)) towards the formation of the
alkoxide.