2.5. Biodiesel purification

The phase separation was carried out in a separation funnel at room temperature. Acid solution of HCl 5% by weight was added to interrupt the reaction, neutralize biodiesel, and promote phase separation. The crude ester phase was purified with distilled water until the pH of the washing water stays neutral. This washing was performed to remove some residues in biodiesel, including excess alcohol and catalyst, glycerin, and soap. After the extraction steps (commonly called biodiesel washing), magnesium sulfate (B'Herzog©, Brazil) was added to the biodiesel to remove moisture. Then, the drying agent was separated from the biodiesel by simple filtration. The final products were analyzed to determine the speed of sound.