Researchers at Los Alamos National Laboratory (LANL), with colleagues at Yale University, have developed a photochemical process to convert acetone derived from plants (bio-acetone) into a mixture of polycyclic alkanes, the high energy density of which is appropriate for high-perfomance aviation applications. A paper on the work appears in the RSC journal Sustainable Energy Fuels.

Synthesis of the alkane mixture from isophorone, which is first produced from bio-acetone. Ryan et al.

This process allows us to transform a natural product into a fuel additive, improving the performance of petroleum-based jet fuel. We converted bio-derived acetone to isophorone and then used a UV lamp to convert it to a cyclobutane, a type of hydrocarbon with high energy density for fuels applications.

—Courtney Ford Ryan, a postdoctoral fellow at Los Alamos National Laboratory and lead author

There are many challenges in using acetone for fuels applications, the paper’s authors note. Its volatility precludes its direct use as a fuel, and it requires chemical upgrading to be suitable for introduction into the fuel supply, as acetone has a nasty habit of dissolving engine parts and O-rings.

By upgrading the initial product to a cyclobutane, a potentially safer and more energy-dense fuel is created, while reducing the hydrogen input required for upgrading a bio-derived feedstock.

The full process first produces isophorone from bio-acetone, the uses photochemical [2 + 2] cycloaddition to generate a cyclobutane dione. Hydro-deoxygenation of the dione yielded the mixture of polycyclic alkanes, in 83% isolated yield.

The photochemical [2 + 2] cycloaddition of isophorone to generate the desired cyclobutane moiety was explored because of its high atom-efficiency, mild reaction conditions, and thoroughly explored photophysics. Isophorone is an apt substrate for this [2 + 2] transformation because of its enone functionality, which allows for the absorption of longer wavelengths of light (greater than 310 nm) and circumvents the need for a photosensitizer. … In this work, the photochemical [2 + 2] coupling of isophorone is high yielding, selective for the head-to-head (HtH) isomer of the dione, and can be performed in water.

—Ryan et al.

The researchers found that while the high energy density of their alkane mixture was suitable for blending with Jet A to improve its performance, the high viscosity of the mixture limits blending to 30% by volume.

It was demonstrated, however, that blending … with Jet-A greatly improved the energy density without compromising the specific energy which may be more applicable to specialized volume limited applications. In this case, the incorporation of renewable carbon, furnished through facile synthetic steps starting from fermentation broth, delivered increased performance to the petroleum-based conventional fuel. This improvement highlights a route to lower the environmental impact of the aviation industry through bio-derived drop-in fuels. In particular, the use of unsaturated bio-derived building blocks to synthesize strained cyclobutanes is a potential path to develop energy dense renewable fuels; however, further testing is necessary to ensure engine compatibility and performance in aircraft.

—Ryan et al.

More work is also needed to make a catalyst that could perform the process using sunlight, Ryan noted.

Funding for the study was provided by the US Department of Energy’s Office of Energy Efficiency & Renewable Energy (EERE) Bioenergy Technologies Office (BETO) through ChemCatBio: Chemical Catalysis for Bioenergy Consortium.

Resources

• Courtney Ford Ryan, Cameron M. Moore, Juan H. Leal, Troy A. Semelsberger, Jenny K. Banh, Junqing Zhu, Charles S. McEnally, Lisa D. Pfefferle, and Andrew D. Sutton (2020) “Synthesis of Aviation Fuel from Bio-Derived Isophorone, Sustainable Energy and Fuels” Sustainable Energy & Fuels doi: 10.1039/C9SE01014A