Conclusions
Analyses of the results show that natural adsorbents were effective in the removal of contaminants of biodiesel, independent of the kind and amount of adsorbent employed. Additionally, from the studied adsorbents, potato starch and cassava starch presented the best compliances when faced with the parameters of ANP standards. For all adsorbents studied via dry washing, there was a decrease in the values relative to the acidity index, combined alkalinity, free glycerine and turbidity, when compared with the pure biodiesel and mainly when compared with the biodiesel purified via wet washing with hot water. It became quite clear that the use of adsorbents for the purification of biodiesel via dry cold washing has the advantage of drastically reducing wastewater, making the process environmentally friendly and avoiding the formation of sub-products by the thermal degradation of biodiesel.