Hydrotreatment of Supercritical Carbon Dioxide Extracts of Hydrothermal Liquefaction Lignocellulosic Biocrude

Raw lignocellulosic biocrude produced by hydrothermal liquefaction and its supercritical carbon dioxide extract (SE) were hydrotreated at 350-405 °C and for 2-6 h utilizing commercial CoMo and NiMo catalysts. The hydrotreatment reduced the oxygen content of the SE down to 1.6 wt %, while the minimum oxygen content of the hydrotreated biocrude (HBC) was 3.1 wt %. No coke formation was observed in the hydrotreatment of the SE, while the yield of coke was 13 wt % when processing the raw biocrude. The hydrotreated SE (HSE) samples exhibited molecular weights 24-61% lower than that of the HBC samples, with larger low-boiling fractions (up to diesel). The better quality of the HSE and the absence of coke, together with the lower metal content of SE (0.2 g/kg) versus BC (8.5 g/kg), suggest that the implementation of hydrotreatment on SEs, instead of raw lignocellulosic biocrude, is a promising option.