A greener alternative to aviation fuel

The Paul Scherrer Institute PSI and the Swiss start-up Metafuels are developing a new process for the production of sustainable aviation fuel (SAF). They are now working together to build and operate the first pilot plant on the PSI campus to validate the technology and prepare it for large-scale commercial use in the near future.

PSI and Metafuels have set themselves the goal of developing and marketing an efficient process for producing affordable synthetic kerosene from renewable raw materials. The plan is to produce high-quality aviation fuel from water, renewable electricity and sustainably obtained carbon dioxide. This sustainable alternative is compatible with existing jet engines, either as an admixture to conventional fossil-based kerosene or ultimately as a primary fuel.

Together with the Metafuels team, PSI researchers have developed a catalytic process that not only avoids the use of fossil raw materials, but also offers superior selectivity, i.e. improved yield/sales compared to alternative SAF technologies. In addition, it enables more efficient use of renewable energy than alternative SAF processes. Scientists from PSI and Metafuels want to use the new proprietary fuel aerobrewTM close the carbon cycle and achieve net-zero aviation.

“Compared to conventional fuel, our technology has the potential to reduce life cycle CO2 emissions by 80 to 95 percent, depending on the production location,” explains Saurabh Kapoor, co-founder of Metafuels. The carbon dioxide required for the technology comes either from Direct Air Capture (DAC) or from non-food biomass such as forestry or crop residues. Water electrolysis produces green hydrogen from renewable electricity, for example from wind or solar systems. “We use hydrogen and carbon dioxide to make synthetic kerosene via the intermediate green methanol.”

Longterm cooperation

For more than a decade, Metafuels co-founders have worked to develop strategies and technologies to support the transition from fossil fuels to renewable energy sources. The three co-founders Leigh Hackett, Saurabh Kapoor and Ulrich Koss not only have enormous scientific and commercial expertise in this field, but also extensive experience in the entire energy sector. You 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 something like that?” was the seemingly simple question. “First of all, of course, we had to carry out many relevant experiments in the laboratory,” recalls Marco Ranocchiari, head of the Energy System Integration (ESI) experimental platform at PSI. “It worked and we were able to validate our scientific concept. Using a catalytic reaction, we were able to develop a process for producing synthetic kerosene from green methanol and at the same time achieve significantly better selectivity than with the alternative SAF technologies.”

Metafuels and PSI are now moving to the next phase of the project, in which a pilot plant will be built and operated. The pilot system will be installed in the form of two container modules on the ESI platform on the PSI campus and integrated into the existing infrastructure. The aim is to validate the technology so that it can be prepared for large-scale commercial use in the near future.

PSI uses the ESI platform in partnership with industry and other research partners to develop and demonstrate processes that promote a CO2-neutral energy system. The focus here is on energy conversion processes that convert renewable energy and raw materials into usable energy sources for a variety of applications, including fuels for transportation.

The most energy-intensive form of travel

Air travel is responsible for around two to three percent of global CO2 emissions. Despite increased awareness of the environmental impact of flying, public appetite for air travel remains high and air travel is expected to continue to increase. In order to achieve the goals of the Paris climate protection agreement and to make air travel climate-neutral in the coming years, intensive research is already being carried out into alternatives.

There are alternatives to synthetic kerosene, such as batteries and hydrogen. However, lithium-ion batteries, as used in electric cars, have a very low gravimetric energy intensity and therefore require enormous mass to provide the energy needed. Batteries are simply too heavy for medium and long-haul flights, where every kilogram counts. In addition, huge adjustments in airport logistics would be required to load many aircraft quickly and simultaneously.

On the other hand, although liquid hydrogen has a higher gravimetric energy density than conventional kerosene, its volumetric energy density is about four times lower. Hydrogen-powered aircraft therefore require a larger tank volume to deliver the corresponding amount of energy. To solve 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 require a complete redesign of aircraft, including the fuel systems and jet propulsion unit.

“The advantage of liquid synthetic kerosene is that it can be integrated directly into the existing airport infrastructure and used in conventional jet engines,” explains Marco Ranocchiari. “So the existing aircraft fleet does not have to be replaced and fossil kerosene can be gradually replaced by synthetic kerosene.”

However, CO2 emissions only account for around a third of the environmental impact of air travel. Equally important, for example, is the formation of contrails. When burning fossil kerosene, jet engines also emit soot particles and other condensation nuclei. At cold temperatures and high altitudes, these immediately form ice crystals that appear as contrails in the sky. Under certain conditions, this can lead to the formation of artificial clouds called aircraft-generated contrail cirrus clouds. Although some of these clouds allow visible sunlight to pass almost unhindered, they efficiently 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, for example, significantly reduce the formation of soot particles,” explains Marco Ranocchiari. Recent research shows that this not only helps reduce the planet’s net warming, but also improves local air quality at airports.

Source: www.eurasiareview.com