Renewable antioxidant additive for biodiesel obtained from black liquor

Black liquor obtained from semichemical pulping of barley straw was depolymerized in a stirred autoclave reactor, at temperature in the range of 250-300 degrees 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 (La), a second one which contains the heaviest compounds precipitated from the liquid at pH 1 (L beta) and a third one obtained by extraction of the acidified liquid (L gamma). The three fractions were tested as antioxidant additives for biodiesel, blending them individually at a dosage of 1 wt%. The antioxidant activity was L alpha > L gamma > L beta. The La 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 (L alpha > L gamma > L beta), 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.