Upgrading of Hydrothermal Liquefaction Biocrude from Forest Residues Using Solvents and Mild Hydrotreating for Use as Co-processing Feed in a Refinery

The presence of a variety of reactive oxygen compounds in biocrudes derived from thermochemical conversion of biomass creates challenges for their co-processing with petroleum in a refinery. In this work, we explore two different technology approaches to upgrade a biocrude produced by hydrothermal liquefaction of forest residues, to the level at which it becomes compatible for co-processing in a refinery. The first approach consisted of using solvents to reject petroleum-insoluble oxygen components in the biocrude, whereas the second one was catalytic hydrotreating under relatively mild conditions. The biocrude had 11.3 wt % oxygen and was completely immiscible in the reference petroleum feedstock (vacuum gas oil). Upgrading using solvents (toluene, dichloromethane, ethyl acetate, and n-pentane) resulted in the rejection of high boiling components, but the concentration of oxygen components in the resulting extract did not change significantly. While the biocrudes treated with n-pentane and toluene were miscible in the reference petroleum feedstock, the mass rejected by these solvents from the biocrude was significant (>35%). Hydrotreating the biocrude was effective at reducing oxygen content down to 2.9 wt % and converting high boiling fractions, while preserving more than 90% of the biocrude's mass as the liquid product. At this level of deoxygenation, the biocrude was fully miscible in the reference petroleum feedstock and the blend was stable over 7 days. NMR spectroscopy provided insights into the structural changes taking place upon hydrotreating the biocrude. In general, it was found that after hydrotreating the biocrude became more saturated in nature and thus more miscible in petroleum.