One of the biggest challenges in reducing greenhouse gas emissions is finding alternatives to fossil fuels in aviation. Switching to electric or hydrogen propulsion is not feasible in the near term, so airlines are looking for ways to use carbon-neutral fuels instead.
A study shows isoprene could be part of the future solution for fossil-free fuels in aircraft. Isoprene can be produced by blue-green algae from sunlight, water, and ordinary carbon dioxide, which is well-suited for photochemical processing into aviation fuels. The productivity of cyanobacteria can be increased with violet light or higher temperatures.
These findings come from two separate studies conducted by the Department of Chemistry – Ångström Laboratory at Uppsala University, which are published in Photochemical and Photobiological Sciences and Bioresource Technology.
“Our study shows that isoprene is actually an ideal hydrocarbon and that the photochemical reaction can be optimized under conditions that are also suitable for photobiological isoprene production,” says Henrik Ottosson, Associate Professor of Physical Organic Chemistry and principal author of one of the studies.
Sustainable aviation fuels (SAFs) are crucial in reducing carbon dioxide emissions from aviation and developing fossil-free aviation fuels. While electric aviation may offer a solution for shorter flights, batteries currently do not provide enough energy for longer flights.
There is emerging interest in creating sustainable aviation fuels through the solar-driven production of hydrocarbons by photosynthetic microorganisms. This could be a promising way to create sustainable aviation fuels and reduce aviation’s carbon footprint.
Two research groups at Uppsala University, led by Henrik Ottosson and Pia Lindberg, have investigated a combined photobiological-photochemical method for producing synthetic sustainable aviation fuel. They have experimented with genetically modified photosynthetic microorganisms called cyanobacteria, which have been engineered to include a new enzyme from the Eucalyptus tree. The enzyme allows the cyanobacteria to produce hydrocarbon isoprene using solar energy and carbon dioxide from the atmosphere.
In a previous study published in November 2022, the same researchers reported that isoprene from cyanobacteria could be dimerized photochemically into larger hydrocarbons, which are similar to existing aviation fuels after hydrogenation. The method seems to have great potential usability as it uses sunlight as the energy source for both processes. However, one question that arises is whether isoprene itself is the best starting material for the photochemical reaction.
Henrik Ottosson’s research group has conducted a study to determine the most suitable hydrocarbon for producing sustainable aviation fuel. They looked at several small hydrocarbons, including those that can be produced through biotechnology.
The study found that the molecular structure of a hydrocarbon affects the efficiency of the photochemical reaction. Despite isoprene’s potential as a fuel and the fact that it can be produced by cyanobacteria, its overall yield is still quite low.
To address this, Pia Lindberg’s research group, in collaboration with the Global Change Research Institute in Brno and others, has conducted a study to identify the optimal cultivation conditions that could increase productivity.
“We can show that both violet light and higher temperatures can increase the productivity of the cyanobacteria. Another finding is that isoprene increases the heat tolerance of cyanobacteria, enabling them to survive at higher temperatures than they normally would, which could be an advantage for large-scale production using sunlight,” says Lindberg, Associate Professor of Microbial Chemistry and author of the other study.
The potential of photobiological and photochemical processes to replace fossil fuels in aviation is promising. However, further development is required to achieve the ultimate goal of setting up an industrial process by 2040.
Journal reference:
- Vajravel, S., Gomes, L. C., Rana, A., and Ottosson, H. Towards combined photobiological-photochemical formation of kerosene-type biofuels: Which small 1, 3-diene photodimerizes most efficiently? Photochemical and Photobiological Sciences, 2023; DOI: 10.1007/s43630-023-00418-0
- Rodrigues, J.S., Kovács, L., Lukeš, M., Hoeper, R., Steuer, R., Červený, J., Lindberg, P. and Zavřel, T. Characterizing isoprene production in cyanobacteria – insights into the effects of light, temperature, and isoprene on Synechocystis sp. PCC 6803. Bioresource Technology, 2023; DOI: 10.1016/j.biortech.2023.129068
- Rana, A., Gomes, L. C., Rodrigues, J. S., Yacout, D. M., Arrou-Vignod, H., Sjölander, J., Vedin, N.P., El Bakouri, O., Stensjö, K., Lindblad, P., Andersson, L., Sundberg, C., Berglund, M., Lindberg, P., Ottosson, H. A combined photobiological–photochemical route to C10 cycloalkane jet fuels from carbon dioxide via isoprene. Green Chemistry, 2022; DOI: 10.1039/D2GC03272D