Obtaining biodiesel antioxidant additives by hydrothermal treatment of lignocellulosic bio-oil

The potential use of bio-oil as a small-dosage additive for improving biodiesel oxidation stability has been investigated in this work. Lignocellulosic bio-oil was high-pressure processed under different mixtures of water and organic solvents in order to promote depolymerization of the high molecular lignin still present in bio-oil and increase the content of phenolics, whose antioxidant potential is known. In fact, the antioxidant potential of bio-oil was found to noticeably enhance after the hydrothermal treatment. While the addition of 2% of crude bio-oil improved biodiesel oxidation stability by 135%, the same amount of hydrotreated bio-oil (water, 300 °C, 8.5 MPa) led to an oxidation stability improvement of 400%, which was related to the increase in the concentration of catechol, as well as to the modification of antioxidant properties of the pyrolytic lignin fraction.