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

Abstract

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 npentane) 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.

Coprocessing Partially Hydrodeoxygenated Hydrothermal Liquefaction Biocrude from Forest Residue in the Vacuum Gas Oil Hydrocracking Process

“…The hydrodeoxygenated HTL biocrude has 3.6 wt % oxygen, which is significantly less than what the raw HTL biocrude had before hydrotreating (11.3 wt % oxygen) . The detailed characterization of the raw HTL biocrude can be found in another publication . VGO is comparatively low in oxygen (0.6 wt %) but has much a higher sulfur content (3.8 wt %) than the hydrodeoxygenated HTL biocrude (<0.1 wt %).…”

“…Table presents the properties of the hydrodeoxygenated HTL biocrude, VGO, and biocrude blend. The hydrodeoxygenated HTL biocrude has 3.6 wt % oxygen, which is significantly less than what the raw HTL biocrude had before hydrotreating (11.3 wt % oxygen) . The detailed characterization of the raw HTL biocrude can be found in another publication .…”

“…Hydrocarbon type determination by SARA analysis shows that VGO is largely composed of aromatics (48.5 wt %) and saturates (36.6 wt %), with a modest amount of resins (also referred to as polars) (14.7 wt %), whereas the hydrodeoxygenated HTL biocrude has comparable quantities of aromatics (34.2 wt %), polars (26.5 wt %), and n -pentane insolubles (27.0 wt %), and some saturates (12.3 wt %). The saturates and aromatics in the biocrude are mostly products of the hydrodeoxygenation process, since the raw HTL biocrude has been reported to have substantially lower amounts of these hydrocarbons . The polars and n -pentane insoluble classes likely constitute the oxygenates and high-boiling components remaining in the HTL biocrude after hydrodeoxygenation.…”

“…Hydrodeoxygenation (HDO), a form of hydrotreatment designed for biogenic feedstocks, is a promising approach that may address the shortcomings of other upgrading methods. Our recent efforts have shown that hydrotreating different HTL biocrudes to about 3 wt % oxygen has resulted in improved miscibility in petroleum VGO, while preserving nearly 90% of the biocrude. , The hydrodeoxygenated HTL biocrude was also shown to have better cohydrotreating performance with VGO than the untreated biocrude. A similar conclusion was reached in a study where raw and hydrodeoxygenated HTL biocrudes were tested for coprocessing with straight-run diesel in a hydrotreating unit.…”

“…Recent studies show that biocrudes can be upgraded by a range of methods, such as distillation, ,, solvent extraction, emulsification, ,, and hydrotreatment. − Distillation has been used for removing high-boiling material in HTL biocrude, thereby producing a distillate that not only was miscible in petroleum vacuum gas oil (VGO) but also could be coprocessed with some degree of success. ,, The major downside of this approach is the significant yield loss of biocrude. Solvent extraction has been recently shown to also be capable of producing petroleum-miscible biocrude extracts but, similar to distillation, at the expense of substantial biocrude mass rejection. Emulsification has been reported to tackle the miscibility problem without mass rejection, ,, yet the effects of coprocessing emulsified biocrude blends are unknown to the best of our knowledge.…”