Improvement of palm oil biodiesel filterability by treatment with reactivated spent bleaching earths

•Spent bleaching earths were reactivated by heating and acid treatment.•The resulting adsorbent was efficient to improve biodiesel filterability.•More than 1 mass% adsorbent is required to achieve the needed filterability.•Reactivation had a negligible effect on crystallinity and morphology of the clay. Reactivation and reuse of Spent Bleaching Earth (SBE) to improve Palm Oil Biodiesel (POB) filterability were examined in this study. The SBE was reactivated by washing with hexane, heating treatment at 500 °C and a combination of heating and acid treatment with 0.1 M HCl solution. The resulting adsorbents, denominated as extracted bleaching earth, calcinated bleaching earth (CBE) and regenerated bleaching earth (RBE), respectively, were characterized by several techniques. Virgin Bleaching Earth (VBE) was also characterized. As a result, solvent extraction of residual oil alone was found not to be an effective method for reactivation of SBE. In contrast, the other two methods tested resulted in an adsorbent capable of achieving the needed filterability. Reactivation was found to have a negligible effect on the crystal structure of the parent clay. It was also found not to alter the layered structure of the clay. SBET of CBE (98.94 m2/g) was smaller than that of VBE (160.11 m2/g), but the amount of N2 adsorbed was not significantly different to each other, evidencing that SBE recovered its initial adsorptive properties after being reactivated. Acid treatment led to a rise in SBET of RBE compared to CBE (121.70 m2/g), but it did not significantly increase its adsorption capacity. This was consistent with EDS analyses, where the content of Al+3, Mg+2, and Fe+3, the octahedral cations susceptible of being dissolved during acid treatment, was not statistically different between RBE and CBE.