Hydrothermal liquefaction of oil-palm-derived lignin to bio-oils for use as antioxidants in biodiesel

Abstract

Lignin extracted from oil palm empty fruit bunch (EFB) fibers was used to produce a phenolics-rich bio-oil via hydrothermal liquefaction in pure water, or an ethanol–water (1:1 v v−1) solvent system, in a stirred batch reactor. The effects of liquefaction temperature (200–300 °C), pressure (10–40 bar), reaction time (0.5–3 h), solvent-to-lignin mass ratio (5–20), and the type of gas (N2, H2, CO2) in the reactor headspace were investigated on the yield and antioxidant properties of the bio-oil. The bio-oil and other products were characterized in detail. The conditions for obtaining a high yield of a bio-oil with a maximum phenolics content and the antioxidant activity were the following: ethanol–water solvent system with a solvent-to-lignin mass ratio of 10, 250 °C, 40 bar, H2 in the headspace, and a reaction time of 2 h. The bio-oil product contained multiple phenolics compounds, and proved to be an effective antioxidant additive in biodiesel made from palm oil. The bio-oil produced under the above specified conditions was a superior antioxidant than butylated hydroxytoluene (BHT), an oxidant used commercially. The bio-oil produced using water as the solvent instead of ethanol–water, was a less effective antioxidant.