Researchers with the US Department of Energy (DOE) Joint BioEnergy Institute (JBEI), with colleagues in China, have produced the tricyclic sesquiterpenes epi-isozizaene, pentalenene and α-isocomene—promising jet fuel feedstocks—at high production titers, providing novel, sustainable alternatives to petroleum-based jet fuels. An open-access paper on their work appears in Biotechnology for Biofuels.

Sesquiterpene compounds (C₁₅) such as farnesene and bisabolene have already been identified as promising jet fuel candidates.

The JBEI team explored three sesquiterpenes—epi-isozizaene, pentalenene and α-isocomene—as novel jet fuel precursors. The researchers performed a computational analysis to calculate the energy of combustion of these sesquiterpenes and found that their specific energies are comparable to commercial jet fuel A-1.

Through bioengineering, they produced 727.9 mg/L epi-isozizaene, 780.3 mg/L pentalenene and 77.5 mg/L α-isocomene in Escherichia coli and 344 mg/L pentalenene in Saccharomyces cerevisiae.

They also introduced a dynamic autoinduction system using previously identified FPP-responsive promoters for inducer-free production and managed to achieve comparable amounts of each compound.

Several microbial platforms have been developed for advanced biofuel production. The advanced biofuels, derived from higher alcohols, alkanes/alkenes, fatty acid esters and isoprenoids, are sustainable energy alternatives, with favorable properties and great market potential. Among these biofuel candidates, C₁₀ and C₁₅ terpenes (monoterpenes and sesquiterpenes) have been increasingly used as jet fuel alternatives for commercial aviation and military purpose because of their structures, suitable carbon numbers and reactive olefin functionality, which collectively impart low freezing points and high energy densities. For example, monoterpenes or monoterpenoids, such as pinenes, linalool and limonene have been used as biosynthetic precursors for aviation and missile fuels such as JP-10, RJ-4 and Jet A-1.

Additionally, the hydrogenated sesquiterpene, farnesane, has been commercialized as a blend stock for jet fuel AMJ-700. Recently, there has been significant interest in multicyclic sesquiterpenes as next-generation jet fuel substitutes due to their high energy density and comparable cetane numbers. For example, three sesquiterpenes, thujopsene, α-cedrene, and β-cedrene, were hydrogenated to generate a fuel blend with 12% higher volumetric net heat of combustion than conventional jet fuel.

In the interest of expanding the scope of multicyclic hydrocarbons as jet fuel alternatives, we sought to produce three novel tricyclic sesquiterpenes: epi-isozizaene, pentalenene and α-isocomene.

—Liu et al.

Resources

• Chun-Li Liu, Tian Tian, Jorge Alonso-Gutierrez, Brett Garabedian, Shuai Wang, Edward E. K. Baidoo, Veronica Benites, Yan Chen, Christopher J. Petzold, Paul D. Adams, Jay D. Keasling, Tianwei TanEmail and Taek Soon Lee (2018) “Renewable production of high density jet fuel precursor sesquiterpenes from Escherichia coli” Biotechnology for Biofuels 11:285 doi: 10.1186/s13068-018-1272-z