Hydrothermal liquefaction of olive oil residues

Abstract Hydrothermal liquefaction (HTL) of olive oil residues was conducted at various temperatures (250, 270, 300 and 330 °C) and residence times (5, 15, 30, and 60 min). The effect of metal chlorides (AlCl3 and SnCl2) on product yields and compositions was investigated under optimum conditions (300 °C for 15 min). Bio-oil and solid residue yields from the non-catalytic run were 30.8 and 31.8 wt%, respectively. Use of metal chlorides led to decreased bio-oil yields and increased solid residue yields. Experiments were also carried out using methanol, with and without catalysts, and under identical conditions. The bio-oil yield from the non-catalytic supercritical methanol liquefaction (SCMEL) was 33.5 wt%, increasing to 40.3 wt% with AlCl3, however, SnCl2 had almost no effect on bio-oil yield. The heating values of bio-oils from HTL runs were higher than those of corresponding SCMEL runs, and the highest heating value of bio-oil (34 MJ/kg) was obtained with AlCl3. Phenols and ketones were major bio-oil constituents in the HTL runs, whereas esters were the most abundant compounds in bio-oils from SCMEL runs.