Materials and methods
2.1. Biodiesel preparation
The biodiesel employed in this study was obtained from commercial sunflower oil (LIZA) by alkaline transesterification via the methyl route. In the method employed for obtaining biodiesel from sunflower, 20% methanol (v/v) and 0.6% NaOH (w/v) were employed as catalysts, with respect to the sunflower oil. Initially, sodium methoxide was obtained by mixing methanol and sodium hydroxide under constant agitation until complete homogenisation. Then, the sodium methoxide was added to the sunflower oil, and the mixture was kept under constant stirring for 30 min, at a temperature of 60 °C. At the end of the reaction, the mixture was transferred to a separatory funnel in order to separate the phases. After resting, we observed two distinct phases: one containing esters, which was less dense and lighter, and the other rich in glycerine, which was denser and darker. After standing for 24 h, glycerine was removed and the resulting biodiesel was employed in the different purification processes studied here [11], [12] and [15].