Fedie, R.L.; McNeff, C.V.; McNeff, C.V.; McNeff, L.C.; Greuel, P.G.; Yan, B.; Jenkins, J.A.; Brethorst, J.T.; Frost, G.B.; Hoye, T.R. Biofuels, Bioprod. Bioref. 2022, 16, 349–369.
The production of green gasoline, jet, and diesel biofuels from waste greases was achieved using a novel hydrothermal, continuous-flow catalytic process operating under supercritical water conditions, with recycled water the only added chemical. Thermally and chemically stable catalysts were explored to optimize yields of liquid biofuels and to minimize production of gases and acidic compounds. A 50:50 mixture of brown and yellow waste greases converted into 76.6 wt% liquid biocrude (BC); the remainder converted to water and gases. Less than 0.2% of the feedstock (FS) formed carbon char (mainly amongst catalyst particles). Various tubular reactors (Inconel, Hastelloy, titanium, stainless) showed no interior defects, erosion, or mass loss after runs. The titanium catalyst was fully recovered and regenerated back to its original potency. The BC was further refined into 28%, 48%, 20%, and 4 wt%, respectively for green gasoline, jet, diesel, and bunker. Biofuels were analyzed for compound class compositions and reaction mechanisms were proposed. Hundreds of identified fuel products (C3-C35) from processing oleic acid as a pure model compound were identified. The neat green gasoline and diesel biofuels, along with a 50% green jet blend (with petroleum Jet A), were tested in appropriate spark ignition, turbine, and diesel engines at the University of Minnesota Engine Labs. The biofuels achieved 107.7%, 97.2%, and 101.3% engine power performance levels relative to petroleum fuels (91-Octane, Jet A, #2 Diesel) along with lower CO and pollutant emissions. The biofuels complied with American Society for Testing and Materials (ASTM) fuel specifications (D4814, D7566, D975) including mandated corrosion and low sulfur limits of all three biofuels.