Biokerosene is two to three times more expensive than normal aviation fuel and, therefore, not economical. Ning Li, Dalian Institute for Chemical Physics, China, and colleagues have developed a synthesis pathway that allows the inexpensive production of high-density aviation fuel from plant material. Such a fuel can significantly increase the range and payload of an aircraft without the need for larger tanks.

In a first step, cellulose is extracted from plant residues such as straw, corn stalks, or sawdust. Dichloromethane is used to selectively convert it into 2,5-hexanedione. At normal pressure and temperature, this reaction produces a yield of more than 70 %. In the next step, the 2,5-hexanedione is repeatedly reacted with hydrogen to form longer chains of ring-shaped hydrocarbons. With the aid of a dual-bed catalyst system, polycycloalkanes with twelve and 18 carbon atoms are formed in an aldol condensation-hydrogenation and hydrodeoxygenation reaction of 2,5-hexanedione and hydrogen. According to the researchers, the resulting hydrocarbon mixture is ideally suited as a high-density aircraft fuel. At the same time, it could also be used as an additive to conventional kerosene to increase its energy density and improve the environmental balance.

According to the scientists, production is cheaper than with conventional high-performance fuel due to the favorable starting materials, only a few reaction steps, and low energy costs. This could make this biofuel competitive. However, the conversion of cellulose requires the toxic and environmentally harmful solvent dichloromethane. The researchers are looking for a sustainable and environmentally friendly substitute.

• Integrated Conversion of Cellulose to High-Density Aviation Fuel,
  Yanting Liu, Guangyi Li, Yancheng Hu, Aiqin Wang, Fang Lu, Ji-Jun Zou, Yu Cong, Ning Li, Tao Zhang,
  Joule 2019.
  https://doi.org/10.1016/j.joule.2019.02.005