Designer Biosynthetic Jet Fuels Derived from Isoprene and α-Olefins

Abstract

Isoprene was hydrovinylated with a series of α-olefins (1-pentene, 1-hexene, 1-heptene, 1-octene) to produce acyclic branched C10–C13 alkenes. The process utilized CoBr2(DPPE) as the precatalyst in loadings as low as 0.1 mol % and zinc as the reducing agent. Use of the cobalt catalyst resulted in primarily 1,4-addition, with carbon coupling at the 4-position of isoprene. A significant amount (∼20%) of the coupling products at the 1-position of isoprene was also observed. Each of the discrete C10, C11, C12, and C13 products were then hydrogenated with 10% Pd/C (200 °C; 650 psi H2) to yield jet fuel blendstocks. In addition to the reactions with pure α-olefins, an equimolar mixture of the C5–C8 α-olefins was used to mimic a stream of olefins produced from ethanol dehydration/oligomerization or Fischer–Tropsch catalysis. The different fuel blends exhibited densities ranging from 0.73 to 0.76 g mL–1, gravimetric net heats of combustion (NHOC) from 43.91 to 44.13 MJ kg–1, and −20 °C kinematic viscosities from 2.4 to 6.3 mm2 s–1. The NHOC values were ∼2.9% higher than the lower limit for Jet-A, while the low-temperature viscosities were up to 70% lower than the upper limit for Jet-A. In addition to studying the suitability of the lightly branched hydrocarbons generated in this process as jet fuel blendstocks, it was of interest to explore their potential as diesel fuels. The equimolar C10–C13 fuel mixture exhibited a derived cetane number (DCN) of 56, which is 16 units higher than that required for Diesel #2 (40). The outstanding fuel properties of the isoprene-derived fuels suggest that they have applications as replacements for both petroleum-derived Jet-A and Diesel #2.