Biocrude oil produced via hydrothermal liquefaction (HTL) of biomass could provide a low-carbon supplement for transportation fuel supply. However, biocrude’s poor chemical (heteroatom content, energy content); physical (viscosity, density); and thermal (boiling point distribution, cetane value, cold-flow properties) characteristics limit commercial application.
Hydrothermal liquefaction (HTL) is a thermochemical depolymerisation process in an enclosed reactor that converts wet biomass into biocrude oil and chemicals at moderate temperature (typically 200–400°C) and high pressure (typically 10–25 MPa).
Product yield and physiochemical properties of HTL are primarily affected by the type of feedstock, processing conditions (primarily reaction temperature and time), and existence of a catalyst. Upgrading of the HTL biocrude is necessary for transportation grade fuel.
Currently, reseachers are mainly focusing on catalytic and hydrogenation processes for upgrading HTL biocrude. However, physical processes—such as fractional distillation as used in oil refineries—are cheaper and more reliable. Distillation cold prove to be a cost-efficient physical technique for biocrude upgrading or even co-processing in a refinery.
Now, researchers in the US and China report achieving the distillation of pilot-scale HTL biocrude derived from food processing waste. Distillation increased the H:C (4.2–13.7%); decreased the O:C (5.5–93.5%), decreased the N:C (6.0–39.0%), and augmented the HHV (4.1–21.3%) compared to the biocrude oil, leading to values of 1.97, 0.003, 0.004, and 52.0 MJ•kg−1, respectively.
These values are similar to the H:C (1.65, 1.94, 2.02), O:C (0.02, ~0, ~0), N:C (0.0002, 0.002, 0.002), and HHV (50.0, 53.1, 53.4 MJ•kg−1) values of gasoline, diesel, and Jet A fuels, respectively.
With respect to the physical properties, distillation decreased the density (23.8–30.5%) and viscosity (99.5–99.9%), while the acidity either increased or decreased depending on the distillation temperature.
Despite the benefits of distillation, blending is still required due to the poor N:C, viscosity, and acidity of the distillates. Theoretical blending calculations determined that blending with Jet A was the most favorable blendstock, amounting to deviations of 63.3–316.6% with the Jet A fuel when the distillate proportion ranged from 10 to 50%.
Their paper is published in the journal Fuel.
Jamison Watson, Buchun Si, Zixin Wang, Tengfei Wang, Amanda Valentine, Yuanhui Zhang (2021) “Towards transportation fuel production from food waste: Potential of biocrude oil distillates for gasoline, diesel, and jet fuel,” Fuel, Volume 301 doi: 10.1016/Jamison
Alireza Taghipour, Jerome A. Ramirez, Richard J. Brown, Thomas J. Rainey (2019) “A review of fractional distillation to improve hydrothermal liquefaction biocrude characteristics; future outlook and prospects,” Renewable and Sustainable Energy Reviews, Volume 115, doi: 10.1016/j.rser.2019.109355