Upgrading of Nondewatered Nondemetallized Lignocellulosic Biocrude from Hydrothermal Liquefaction Using Supercritical Carbon Dioxide

Supercritical carbon dioxide (sCO₂) extraction was applied on a raw biocrude, obtained by hydrothermal liquefaction of pinewood. The extractions were carried out in a semicontinuous mode, in the ranges of 80 to 150 °C and 330 to 450 bar. Extraction yields from 44 to 53 wt % were achieved. The extracts were richer in lower-molecular-weight (MW) compounds, with fatty acids and aromatic hydrocarbons concentrated up to 14 and 24 wt %, respectively. For comparable MWs, lower-polarity compounds concentrated in the extracts. Compared to the feed, the extracts exhibited a lower density (from 1030 kg/m³ down to 914 kg/m³), lower water content (from 5.7 wt % down to 1.3 wt %), and lower oxygen content (from 10.0 wt % down to 5.0 wt %). In addition, the metal content was drastically reduced (from 8500 mg/kg down to 170 mg/kg on average). In the context of biofuel production, the sCO₂ extracts are a better feed for catalytic hydrotreating.