POWER-TO-LIQUID (PTL) SAF PRODUCTION PATHWAY

airlines of the International Air Transport Association (IATA) committed to achieve net zero carbon emissions from their operations by 2050. Besides new aircraft technologies, more efficient operations, direct carbon capture (DCC) and credible offsetting schemes, the main hope of making aviation sustainable rests on sustainable aviation fuel (SAF). Indeed, as much as 65 per cent of the reduction of GHG emissions required to attain IATA’s challenging net zero goal is expected to come from SAF.

WHAT IS SAF?

SAF is an umbrella term for all aviation fuels produced without the use of fossil energy. The term “sustainable” highlights the fact that the production process does not have a detrimental impact on the environment, since it involves neither deforestation nor land use change, nor does it require large amounts of fresh water. It also implies that the feedstock is obtained by focusing on waste-to-fuel and power-to-liquid (PtL) solutions, not by grabbing arable land from farmers. By design, SAFs are “drop-in” fuels that can be directly blended into existing airport infrastructure and are fully compatible with modern airliners.

Saf Technologies

A common misconception is that SAF is one particular type of fuel. In fact, SAFs can be produced from a variety of feedstocks (42 at last count) and through several different technologies, each with its own set of challenges. As of April 2023, nine conversion processes for SAF production have been approved and eight others are under evaluation by ASTM International. Researchers are continuously developing and refining new ways to create SAF and to produce it at lower cost from an expanding set of technologies and feedstocks.

• First Generation SAFs: These are the cheapest, simplest to produce and hence most commonly available type. They come from fats, oils and greases (FOGs). They reduce CO2 emissions by 50 to 80 per cent compared to normal jet fuel over the lifecycle of the product. The obvious problem is limited availability of feedstocks which prevents significant scaling up of production.

• Second Generation SAFs: These types of SAF are obtained from biomass and municipal solid waste and can poten- tially reduce GHG emissions by 85 to 95 per cent over their lifecycle. Biomass may include algae, crop residues, animal waste, sludge and forestry residue. However, production often requires advanced technologies and complex processes, such as thermochemical or biochemical conversion, that can be rather expensive and energy-intensive.

PtL – THE NEXT GENERATION

The most promising technology for SAF, albeit currently the most expensive, is PtL. PtL SAF involves the production of synthetic liquid hydrocarbon fuel using green hydrogen and non-fossil CO2 as the main feedstocks. This SAF process can potentially reduce GHG emissions by as much as 99 per cent especially if it uses CO2 obtained by direct air capture (DAC) and green hydrogen produced through electrolysis using renewable electricity. With a practically infinite supply of CO2 as feedstock, progress can be made towards a circular carbon economy. PtL processes vary. But all have in common the creation of a mixture of hydrogen and carbon monoxide, known as syngas. At appropriate temperatures and pressures, syngas can be processed to yield hydrocarbons and water through the FischerTropsch process.

In November 2021, in a world-first, an Ikarus C42 microlight aircraft flown by an RAF pilot completed a short flight in the UK powered entirely by synthetic fuel. Zero Petroleum’s UL91 fuel is manufactured by extracting hydrogen from water and carbon from atmospheric CO2. Using energy generated from renewable sources like wind or solar, these are combined to create the synthetic fuel.

In February 2023, SAF developer Air Company was awarded a contract by the US Air Force (USAF) to install its technology at various USAF bases. According to the USAF, Airmade SAF is the first fuel made entirely from CO2 emissions that matches the properties and performance of jet A-1 fuel, including aromatics. The fuel is net carbon neutral requiring as much captured carbon input as is emitted when it is burned. Therefore, instead of increasing emissions, it is recycling them.

For And Against Saf

Some of the key benefits of SAF (to use the singular term for