Power to Liquid (PtL) Synthetic Aviation Fuel - A Sustainable Pathway for Jet Fuel Production 2021-36-0034
Aviation industry currently accounts for almost 3% of worldwide greenhouse gas (GHG) emissions. Despite the continuous efforts to reduce this environmental footprint, with the use of technological efficiency driven solutions and operational changes to reduce climatic effects, such as engine improvements, fleet renewals and navigation operational improvements, the industry, which is permanently challenged by the continuously stringent standards, is aware of the need of additional measures to tackle, and even reduce, the GHG emissions, by decoupling the world's industry average growth (almost 4.1% annually) to the aviation's carbon emissions. Given its inherent operational features, the aviation sector requires fuels with high specific energy and energy density. This technical requirement makes the well known clean and efficient electrical propulsion technology to be limited to niche aviation segments (short range and low capacity airplanes) in the short and medium terms. In this scenario, the so called Sustainable Aviation Fuels(SAF) - non fossil hydrocarbons, manufactured with renewable & sustainable feedstocks - appear as the big bet for the carbon footprint reduction for the medium and long range aviation. The biofuel SAF pathway, i.e. that which relies on biological feedstocks (crops and waste), already certified and produced to be used in blends with fossil jet fuel, into a drop-in fuel concept, has some environmental limitations associated with GHG net emissions, cost, and natural resources (land use and water) requirements. These limitations might set sustainable challenges to a massive future biofuel based SAF approach. In this context, the so called Power to Liquids (PtL) fuels, which comprises the production of synthetic liquid hydrocarbon fuels, using renewable electricity (for hydrogen generation with water electrolysis) and non fossil carbon dioxide (CO2) as the main feedstocks, is seen as a promising SAF pathway. Compared to biofuels, PtL SAF reaches higher area-related yields, with the intensive use of renewable electricity, such as photovoltaic and wind energy. The PtL's SAF water requirement is also significantly lower, compared to the biofuel production. Hence, the PtL SAF technology is seen as an important SAF pathway to enable a non fossil and fully sustainable fuel supply for aviation in the long run, avoiding the risks and adverse effects potentially associated with biomass based pathways. This work presents, based on an assessment of the researched technical literature, an overview of the PtL SAF technology, with a focus on the production methods and the required inputs, followed by an assessment of operational effects and costs for the aviation sector. The analysis shows that the PtL SAF appears as a promising sustainable SAF pathway, with a lower GHG footprint (into a Lyfecycle basis) and reduced water requirement, as well as a higher yield, compared to the plant-based SAF pathways (biofuels). Moreover, PtL SAF does not raise the demand for arable land, avoiding the so called food & fuel conflict. From a technical perspective, the PtL SAF might produce fuels suitable for even a net fossil fuel substitution (no blends). Nevertheless, the PtL SAF costs, which relies strongly on the renewable electricity price, are still a challenge to enable the competition with fossil jet fuel. This might initially require regulatory actions as well as further technological improvements, mainly associated with renewable electricity - fuel conversion and CO2 supply alternatives.