A variety of technologies have been developed to produce renewable jet fuels from biomass feedstocks. For instance, UOP/Honeywell and Neste developed the hydrogenated esters and fatty acids (HEFA) processes to upgrade vegetable oils and animal fats to renewable jet/diesel fuels. The synthesis of bio-jet fuels from lignocelluloses has also drawn much attention. However, most of the reported bio-jet fuels are primarily composed of linear or branched chain alkanes. Such bio-jet fuels suffer from low densities (~0.76 g/mL) and low volumetric heating values compared with those of petro-jet fuels. Currently, most alternative fuels have to blend with petro-jet fuels to meet the energy density requirements. In addition to jet fuels, specialty military fuels for missile propulsion such as JP-10 (composed almost exclusively of exotetrahydrodicyclopentadiene) have even more demanding high density requirements. These standards cannot be met by current renewables and require specialized fuel mixtures.

Cyclic hydrocarbons (i.e. cycloalkanes), instead, can be used to make dense jet fuels with high thermal stability. However, the industrial synthesis route to produce cycloalkanes is high in cost and the precursor from hydrocracking of petroleum has low selectivity. … the current technologies of producing bio-derived cycloalkanes are still far from cost-competitive in large scales.

Terpenoids (e.g., isoprenoids), containing one or more cyclic hydrocarbon rings, are commonly found in many biomass genera such as mint, pine, eucalyptus, etc. … Herein, we design a novel biphasic tandem catalysis process (biTCP) aiming to highly efficiently convert terpenoids to cycloalkanes.

—Yang et al.

In the biTCP, both hydrophilic and hydrophobic catalysts are added into two immiscible solvents—an organic phase and an aqueous phase—creating a biphasic environment for a “cascade” of chemical reactions in both phases. This approach of biphasic tandem catalysis not only reserves the feature of convenient catalyst/product separation but also accomplishes multiple reaction steps in a “one-pot” process.

Multistep tandem reactions, including C-O ring opening by hydrolysis, dehydration, and hydrogenation, were carried out in the “one-pot” biTCP. Terpenoid biomass (1,8-cineole) was efficiently converted to p-menthane at high yields (>99%) in the biTCP under mild reaction conditions.

The biTCP demonstrated a much higher carbon efficiency than those of other single-phase processes; the biTCP concept has the potential to be generalized for the conversion of various biomass feedstocks to renewable hydrocarbon fuels with high carbon efficiencies, the researchers suggested.

Resources

• Xiaokun Yang, Teng Li, Kan Tang, Xinpei Zhou, Mi Lu, Whalmany L. Ounkham, Stephen M. Spain, Brian J. Frost and Hongfei Lin (2017) “Highly efficient conversion of terpenoid biomass to jet-fuel range cycloalkanes in a biphasic tandem catalytic process” Green Chem. 19, 3566-3573 doi: 10.1039/C7GC00710H