The Paul Scherrer Institute PSI and the Swiss start-up Metafuels are developing a new process for producing sustainable aviation fuel (SAF). They are now collaborating on the construction and operation of the first pilot plant on the PSI campus to validate the technology and prepare it for large-scale commercial deployment in the near future.
PSI and Metafuels have set themselves the goal of developing and commercializing an efficient process for producing affordable synthetic jet fuel from renewable resources. The plan is to produce high quality aviation fuel using sustainably sourced water, renewable electricity and carbon dioxide. This sustainable alternative is compatible with existing jet engines, either blended with traditional fossil kerosene or optionally as a primary fuel.
Together with the Metafuels team, the PSI researchers have developed a catalytic process which not only avoids the use of fossil raw materials, but also offers superior selectivity, in other words improving the yield/conversion compared to alternative SAF technologies. In addition, it allows renewable energy to be used more efficiently than in alternative SAF processes. PSI and Metafuels scientists want to use the new proprietary fuel aerobrewMT to close the carbon cycle and reach net zero in air transport.
“Compared to traditional fuel, our technology has the potential to reduce lifecycle carbon emissions by 80-95% depending on the production site,” says Saurabh Kapoor, co-founder of Metafuels. The carbon dioxide needed for the technology comes either from direct air capture (DAC) or from non-food biomass such as forestry or crop residues. The electrolysis of water produces green hydrogen from renewable electricity, for example from wind or solar installations. “We use hydrogen and carbon dioxide to produce synthetic kerosene via intermediate green methanol.”
For more than a decade, the co-founders of Metafuels have been working to develop strategies and technologies to support the transition from fossil fuels to renewable energies. The three co-founders, Leigh Hackett, Saurabh Kapoor and Ulrich Koss, not only have tremendous scientific and business expertise in this area, but also extensive experience in the energy industry as a whole. They have previously worked on complex challenges related to the decarbonization of energy systems. The aviation industry now offers them a new challenge.
Metafuels approached PSI with a definitive business plan and technology path. “Can you do that sort of thing?” was the seemingly simple question. “First of all, of course, we had to perform a lot of relevant experiments in the laboratory,” recalls Marco Ranocchiari, head of the Energy Systems Integration (ESI) experimental platform at PSI. “It worked and we were able to confirm our scientific concept. We were able to use a catalytic reaction to develop a process for producing synthetic kerosene from green methanol and at the same time achieve significantly better selectivity than with alternative SAF technologies.
Metafuels and PSI are now progressing into the next phase of the project during which a pilot plant will be built and operated. The pilot plant will take the form of two container modules to be installed on the ESI platform of the PSI campus and to be integrated into the existing infrastructure. The goal is to validate the technology so that it can be prepared for large-scale commercial use in the near future.
PSI, in partnership with industry and other research partners, uses the ESI platform to develop and demonstrate processes that promote a carbon-neutral energy system. The focus here is on energy conversion processes that convert renewable energy and raw materials into usable energy sources for a wide range of applications, including transportation fuels.
The most energy-intensive mode of transport
Air transport is responsible for around 2 to 3% of global CO2 emissions. Despite greater awareness of the environmental impact of flying, public appetite for air travel remains high and air traffic is expected to increase further. To achieve the goals of the Paris Agreement on climate change and make air transport carbon neutral in the years to come, an intensive search for alternatives is already underway.
Alternatives to synthetic kerosene exist, such as batteries and hydrogen. However, the type of lithium-ion batteries used in electric cars have a very low gravimetric energy intensity and therefore require enormous mass to provide the required energy. For medium and long-haul flights, where every kilogram counts, the batteries are simply too heavy. In addition, huge adjustments in airport logistics would be required for rapid and simultaneous recharging of many aircraft.
On the other hand, although liquid hydrogen has a higher gravimetric energy density than traditional kerosene, its volumetric energy density is about four times lower. Hydrogen aircraft therefore require a larger tank volume to provide the corresponding amount of energy. To overcome this problem, Airbus, for example, is developing a hybrid technology that burns hydrogen in gas turbines on the one hand and converts it into electricity in fuel cells on the other. However, this would involve a complete overhaul of the aircraft, including the fuel systems and the jet propulsion unit.
“The advantage of liquid synthetic kerosene is that it can be integrated directly into existing airport infrastructure and can be used in conventional jet engines,” explains Marco Ranocchiari. “So no need to replace the existing aircraft fleet, and fossil-based kerosene can be gradually replaced by synthetic kerosene.”
However, CO2 emissions account for only about a third of the environmental impact of air travel. The formation of contrails, for example, is just as important. By burning fossil kerosene, jet engines also emit soot particles and other condensation nuclei. At cold temperatures and at high altitudes, they instantly form ice crystals that appear as contrails in the sky. Under certain conditions, this can lead to the formation of artificial clouds, known as trailing cirrus produced by aircraft. Although some of these clouds allow visible sunlight to pass almost unhindered, they very effectively reflect and absorb infrared rays from the Earth’s surface, preventing the radiation from escaping into space.
“The molecular composition of synthetic fuels makes it possible to manipulate the combustion process and significantly reduce the formation of soot particles, for example,” explains Marco Ranocchiari. The latest research results indicate that this not only helps reduce net global warming, but also improves local air quality at airports.