Branched Ketone Biofuels as Blending Agents for Jet-A1 Aviation Kerosene

In this investigation a range of ketone biofuels produced from the alkylation of isoamyl alcohol and isobutanol were examined as potential blending agents with Jet A-1 aviation kerosene. The fuels were synthesized under solvent-free conditions using a Pd/C catalyst with K3PO4, previously reported for the alkylation of acetone, butanol, and ethanol (ABE) fermentation mixtures. Reasonable yields and selectivity were achieved for branched alkylation products with up to 61% produced from isoamyl alcohol and 64% from isobutanol. The key aviation fuel properties of the mixtures were tested unblended and in 50% and 20% blends with Jet A-1 aviation kerosene. The freezing points of the fuels were all found to be below the required −47 °C irrespective of blend or the temperature of the reaction. The energy density of the unblended fuels ranged between 30.4 and 41.36 MJ/kg depending on the temperature of the reaction and whether remaining alcohols were removed. While this is below the higher heating value (HHV) of the Jet A-1 used (45.69 MJ/kg), the energy densities of the 50% and 20% blends were more suitable with the isoamyl alcohol derived fuels having a maximum HHV of 44.31 MJ/kg at 50% blending and 44.99 MJ/kg at 20% blend with Jet A-1. The fuels derived from isoamyl alcohol produced above 140 °C were found to satisfy the flash point criterion (>38 °C) of the Jet A-1 specification, though the isobutanol derived fuels did not, producing fuels with flash points between 33 and 35 °C. The kinematic viscosities of the fuels were also tested at −20 °C. Unblended only a few of the fuels analyzed met the maximum viscosity requirement at −20 °C of 8 mm2 s–1, though this fuel property was improved substantially on blending with jet fuel. This work demonstrates that ketones produced from isoamyl alcohol through a simple alkylation have the potential to be used as blending agents with Jet A-1.