Results and discussions
The yield of biodiesel, obtained in the transesterification process employed in this study, was 87% (calculated in relation to the initial mass of oil and the final mass of biodiesel fraction). This value is in agreement with the values found in the literature [4], [7], [11], [12] and [15]. Fig. 1 shows the SEM images of the adsorbents employed in the purification processes carried out in this work. It is possible to verify the different morphologies and sizes of the samples. The corn starch, rice starch and Select 450® are polyhedral, the potato starch is ellipsoidal, the cassava starch is semi-spherical, and the cellulose is in tape format. The sizes of the adsorbent particles estimated from the SEM images are presented in Table 1. Both the morphologies and sizes of the samples are in agreement with the values reported in the literature [20]. These differences in size and shapes can reflect, mainly, the sizes of the surface areas of the particles, and hence can perform different roles in the processes of adsorption of impurities from the biodiesel. Although was observed differences of the particle sizes from SEM images, it is possible see from Table 1, that the values of the surface area and pore sizes were not significantly different for the starch and cellulose samples. Additionally, it was observed that the surface area and pore size for Select 450® is very higher than that observed for cellulose and starch samples.