Renewable Diesel Fuel Prepared by the Isomerization and Hydrogenation of Biosynthetic Farnesene

There are a number of different routes for the production of renewable diesel from lipid and crude biomass sources. Most of these approaches generate acyclic hydrocarbons that offer high gravimetric net heats of combustion (NHOC) and good combustion properties, but much lower densities than petroleum-based diesel fuel. To address this shortcoming, biosynthetic farnesene was isomerized with a heterogeneous acid catalyst (Amberlyst-15) under mild conditions and hydrogenated to generate a complex mixture of acyclic, monocyclic, bicyclic, and tricyclic hydrocarbons. The hydrogenated farnesene isomers (HFI) had a density of 0.852 g mL–1, a gravimetric NHOC of 43.33 MJ kg–1, a 40 °C kinematic viscosity of 3.25 mm2 s–1, and a derived cetane number (DCN) of 40. All of these values are similar to or exceed those of diesel fuel derived from petroleum sources. Compared to farnesane, the direct hydrogenation product of farnesene, HFI exhibited 11% higher density and 9% higher volumetric NHOC due to the cyclic compounds contained in the mixture. 10–40% blends of HFI with conventional jet fuel were prepared and exhibited −20 °C kinematic viscosities ranging from 4.8–7.8 mm2 s–1, which fall within the specification for Jet-A (<8.0 mm2 s–1). Overall, acid-catalyzed isomerization of farnesene resulted in an upgraded diesel product that can be easily integrated into current supply chains. This result provides further evidence that hybrid synthetic protocols combining biosynthetic and chemical steps are powerful approaches to the development of next-generation renewable diesel and jet fuels.