Biodiesel production by two-stage transesterification with ethanol by washing with neutral water and water saturated with carbon dioxide

► A first washing with neutral water improves the purification procedure. ► Water saturated with CO2 can be used as the second purification step. ► Lower acidity in the final biodiesel is obtained using this procedure. ► This procedure successfully purified biodiesel with high soap content. ► Conventional acid-washing cannot be used in case of high soap containing biodiesel.