Renewable antioxidant additive for biodiesel obtained from black liquor

Abstract Black liquor obtained from semichemical pulping of barley straw was depolymerized in a stirred autoclave reactor, at temperature in the range of 250–300 °C while varying the amount of catalyst (zeolite Y). Three fractions were obtained from the depolymerized liquor: a fraction directly extracted from the liquid with isopropyl acetate (Lα), a second one which contains the heaviest compounds precipitated from the liquid at pH 1 (Lβ) and a third one obtained by extraction of the acidified liquid (Lγ). The three fractions were tested as antioxidant additives for biodiesel, blending them individually at a dosage of 1 wt%. The antioxidant activity was Lα > Lγ > Lβ. The Lα fraction showed the highest antioxidant activity, increasing the oxidation stability time over neat biodiesel from 150 to 250%. The phenolic volatile content of the fractions (measured by GC/MS) decreased in the same rank (Lα > Lγ > Lβ), so there doesn’t seem to be correlation between the volatile content and the increase of antioxidant activity. Depolymerizarion temperature was the most influential parameter, showing a clear positive effect on the antioxidant activity for the three fractions.