In the quest to find fossil-free fuels for aircraft, a new study shows that isoprene could be part of a future solution. Isoprene can be produced by blue-green algae, cyanobacteria, from sunlight, water and ordinary carbon dioxide, and the cyanobacteria's productivity increases if they are exposed to violet light or higher temperatures.
This is the result of two different studies from the Department of Chemistry – Ångström, at Uppsala University, which are now published in Photochemical & Photobiological Sciences and Bioresource Technology, respectively.
“Our study shows that isoprene is actually an ideal hydrocarbon, and that the photochemical reaction can be optimized for conditions that are also suitable for photobiological isoprene production,” says Henrik Ottosson, senior lecturer in physical organic chemistry and lead author of one of the studies.
Sustainable aviation fuel, SAF, is an important part of the development of fossil-free aviation fuels, and ultimately reducing aviation's carbon dioxide emissions. Although electric aviation may be another solution, especially for short flights, today's battery capacity is not sufficient for longer flights. A new way to create sustainable aviation fuel could be through sunlight-driven production of hydrocarbons by photosynthetic microorganisms.
Two research groups at Uppsala University, led by Henrik Ottosson and Pia Lindberg respectively, have investigated a combined photobiological-photochemical method for the production of synthetic sustainable aviation fuel. In their research, they have used genetically modified photosynthetic microorganisms, cyanobacteria, which have been genetically engineered to receive a new enzyme from the eucalyptus tree. With the enzyme, the cyanobacteria can use sunlight and ordinary carbon dioxide found in the air to produce the hydrocarbon isoprene.
In a previous study, published in November 2022, the same researchers reported that isoprene from cyanobacteria can be photochemically dimerized to larger hydrocarbons that, after hydrogenation, are very similar to the aviation fuels used today. The method has the potential to be very useful, as it uses sunlight as the energy source for both steps. One question, however, is whether isoprene is the best starting material for the photochemical reaction.
To find out whether it is isoprene or whether there are other hydrocarbons that are best suited to produce a sustainable aviation fuel, Henrik Ottosson's research group has investigated a series of different small hydrocarbons, several of which can be produced biotechnologically. The results of the study show how the molecular structure of a hydrocarbon affects how efficiently it undergoes the photochemical reaction.
Although isoprene can be produced by cyanobacteria, the amount formed is still very low. Therefore, Pia Lindberg's research group, in collaboration with, among others, the Global Change Research Institute in Brno, Czech Republic, has conducted a study to investigate which cultivation conditions can affect productivity.
"We can show that violet light or higher temperatures can give higher productivity from the cyanobacteria. It can also be seen that isoprene gives the cyanobacteria better heat tolerance so that they survive at higher temperatures than normal, which could be good for larger-scale production using sunlight," says Pia Lindberg, senior lecturer in microbial chemistry and lead author of the second study.
The results from the photobiological and photochemical sub-steps improve the possibilities of replacing fossil sources for aviation fuel. The technology will need to be developed so that the ultimate goal of an established industrial process by 2040 can be realized.
Source: According to Press Release.
