Co-hydrotreatment of Bio-oil and Waste Cooking Oil to Produce Transportation Fuels

This paper reports the co-hydrotreatment of the heavy bio-oil fraction with waste cooking oil (WCO) using the NiMo/γ-Al₂O₃ catalyst, followed by the distillation of the resulting deoxygenated oil and the characterization of the resulting fuel cuts. The heavy Biomass Technology Group (BTG) bio-oil fraction was obtained by removing the very reactive light-oxygenated compounds via rotary evaporation and subsequently mixed with 1-butanol. The resulting oil was blended with WCO and subjected to a two-step co-hydrotreatment process. The first step, called “stabilization,” was aimed at saturating highly reactive hydrogen-deficient compounds. The second step, called “deoxygenation,” aimed to remove bio-oil oxygen, primarily as H₂O. This study examined the impact of varying bio-oil concentrations (0, 10, 20, 30, 40 wt % of WCO) on the upgraded oil’s yield, composition, and fuel properties. The resulting hydrotreated oil was distilled into gasoline-range, kerosene-range, and diesel-range hydrocarbons at <150, 150–250, and 250–350 °C, respectively. The yield of the hydrotreated oil indicated that as the bio-oil concentration increased, the amounts of coke (0.7–2.4%) and water (2–10 wt %) increased, while the organic layer yields decreased (80–63%). The coke yield was comparable to the coke yield obtained when co-processing the pyrolytic lignin fraction. This suggested that coke was formed from both the sugar oligomers and the lignin-derived oligomers. The UV fluorescence analysis on the hydrotreated oil showed that more polycondensed and conjugated ring compounds formed as the bio-oil concentration was increased. These compounds are precursors of coke. Fourier transform infrared spectroscopy (FTIR) results showed that most raw materials were converted to biofuels after the hydrotreatment. To achieve less than 1 wt % of coke yield, blends with up to 20 wt % pyrolysis oil should be used. An increase in the bio-oil concentration led to a slight increase in the gasoline yield and a decrease in kerosene and diesel yields. The identified carbon species found in the fuel cuts included n-paraffin, iso-paraffin, cycloparaffin, and aromatics. Further, the jet fuel cut (kerosene) was characterized by density, surface tension, and viscosity. Our product conforms to the standard specifications for sustainable aviation fuels (Jet A-1). Further research is suggested to fine-tune the operating parameters for achieving reduced coke yield and enhanced kerosene yield.