About 50 g sample of unpurified biodiesel was transferred to a125 mL Erlenmeyer flask and the purification was performed in a batch mode under heating at 65 °C and stirring. The concentration of the adsorbent in the sample was
but with concentrations of 1%, 2%, 3%, 4% and 5% (w/w). The RHA did not suffer any previous treatment. The purified biodiesel was filtered through a simple funnel with filter paper to remove the adsorbent and stored for later analysis. Each one purification was done in duplicate