Purification of biodiesel by dry washing, employing starch and cellulose as natural adsorbents

• Biodiesel from sunflower oil was successfully purified with natural adsorbents.
• Starch from different sources and cellulose fibers were used as adsorbents.
• Dry washing has removed more impurities than the wet washing.
• Was reduced the acidity index, alkalinity, free glycerine and turbidity of biodiesel.

This work describes a study of the purification of biodiesel produced from sunflower oil by dry cold washing using natural adsorbents as cellulose and starch from different sources (corn, potato, cassava and rice), and the comparison with dry cold washing with a commercial adsorbent Select 450® and with the conventional wet washing with hot water. The purification by dry washing was carried out by varying the amount of adsorbents in 1%, 2%, 5% and 10% (w/v) at 25 °C for 10 min. For the purification by wet washing, the biodiesel was successively washed with acidified water and pure water at 85 °C until neutralisation. The efficiency of the processes for the removal of biodiesel impurities was evaluated by determining the acidity index, combined alkalinity, free glycerine and turbidity of the biodiesel. All adsorbents studied presented good efficiency in the removal of the impurities and showed similar behaviour independent of the kind or amount of adsorbent employed. The use of natural adsorbents for the purification of biodiesel have been shown to be a promissory process to be applied as an industrial stage of the purification of biodiesel during their production.