Biodiesel Dry Purification Using Unconventional Bioadsorbents

The dry washing method is an alternative to replace water washing, thereby reducing the negative impacts of contamination. However, commercial adsorbents come from industrial processes that, due to their composition, may not be such a sustainable resource in the global biodiesel production process. In this study, the use of organic residues, such as sawdust, coconut fiber, nutshell, rice husk, and water hyacinth fiber, were proposed as bioadsorbents for the purification of biodiesel from waste cooking oil. Quality parameters such as the acid number, water content, and free and total glycerin content were evaluated and compared with those after purification with commercial adsorbents (Magnesol and Amberlite BD10DRY). Promising results were obtained using sawdust in the purification process, achieving a reduction in the acid number value of 31.3% respect to the unpurified biodiesel. Indeed, the reduction with sawdust was more efficient than with Amberlite BD10DRY (that increased the acid number). In addition, sawdust reduced free glycerin by 54.8%, again more efficient than Amberlite BD10DRY. The total glycerin values were similar between commercial adsorbents and sawdust. Water content after purification with sawdust was similar to the obtained with Amberlite BD10DRY and better than with Magnesol (399, 417, and 663 mg/kg respectively). These results show that sawdust can be used as an alternative bioadsorbent in a dry purification method for biodiesel, generating less environmental impact.