(589e) Upgrading of Hydrothermal Liquefaction Biocrude Oil Converted from Wet Biowaste

Wet biowaste is an increasingly studied feedstock for producing renewable bioenergy, reusing nutrients and improving the environment. Each year, the United States produces 79 million dry tons of wet biowastes from food processing and livestock manure and could be recovered as renewable energy. One of the limitations for wet biowaste to energy conversion is the high water content (80-99%).

Hydrothermal liquefaction (HTL) is a technology to reduce complex organic materials into biocrude oil and an aqueous fraction containing original nutrients and wastewater. Research has shown that HTL can convert 30-70% of different volatile solids into biocrude oil with heating values between 32-38 MJ/kg. HTL biocrude oil converted from different types of wet biowastes contains impurities: 10-20% oxygen, 3-7% nitrogen, and up to 20% of moisture. It is necessary to separate and/or upgrade the HTL biocrude oil for transportation fuel application. Distillation can reduce the oxygen content in the biocrude oil to 5% and increase the heating value to 41-45 MJ/kg. We hypothesize that with appropriate separation techniques, such as distillation, the HTL biocrude oil can be separated into different fractions, and some fractions can be used as transportation fuel including aviation fuel and diesel.

Our initial results suggest that distillation of HTL biocrude oil converted from swine manure (SW) and food processing waste (FPW) is very promising. Analyses demonstrate that the distillates from SW- and FPW-derived biocrude, respectively, contain 15 wt.% and 45-50 wt.% fractions that have heating values similar to those of petroleum aviation fuel and diesel without any further upgrading. In addition, an aviation biofuel blend prepared with 10 wt.% HTL distillates with the highest heating values (46-47 MJ/kg) and 90 wt.% petroleum jet fuel (or bio-kerosene BK10), exhibited the same properties including density, viscosity (6.3% lower), total sulfur content, copper corrosion performance, and net heat of combustion (1.30% lower) as those of commercial petroleum jet fuel. Although the distillation significantly improved the fuel's properties, more improvement is needed for use in current engines. For instance, the BK 10 blend had four times the acidity and a 20% lower flash point than those of petroleum jet fuel. We also found that oxygenates and nitrogen-containing compounds in the distillates from SW-derived biocrude led to excessive gum in BK10 blend. Thus, additional upgradation is needed. 

Two strategies were investigated to make the HTL distillates converted from SW and FPW more compatible with petroleum transportation fuels. First, esterification was conducted to reduce the acidity in FPW-derived distillates. An orthogonal experimental design was operated to examine the effect of reaction temperature, reaction time, the catalyst loading (H₂SO₄), and the molar ratio of methanol on the esterification yield and acidity of the distillates. After esterification, the acidity of the distillates was reduced from 27.5 mg KOH/g to 0.8-7.3 with a yield of about 88 wt.%. The highest esterification yield was achieved at 70 °C for a 0.5 h reaction time with 2 wt.% catalyst loading under a 1:9 molar ratio of methanol; and the lowest acidity was realized at 50 °C for a 2h reaction time with 2 wt.% catalyst under a 1:15 molar ratio of methanol. The orthogonal test also indicates that the reaction time impacted the esterification yield the most, while the reaction temperature affected the acidity the most. 

On the other hand, catalytic deoxygenation and denitrogenation under sub-/supercritical water are investigated to reduce the oxygen and nitrogen contents in the SW-derived distillates to reduce gum contents for BK10 blend. Preliminary data showed that supercritical water is a promising reaction media to inhibit the char formation and promote deoxygenation/denitrogenation for SW-derived distillates. Different types of catalysts (e.g., Raney-Ni), reaction temperature, reaction time, and reaction media (e.g., supercritical water) are examined. The physicochemical properties of the upgraded distillates are analyzed to elucidate the upgrading mechanism. Elemental compositions, chemical compositions, heating values, flash point, viscosity, gum, and ash contents of the upgraded distillates are characterized and compared to those without upgrading.