Europe’s rules on CO2 sourcing for power-to-liquids fuels could derail one of our best hopes for clean aviation. By Andrew Symes 

Europe’s recent sustainable aviation fuel (SAF) rules risk undermining one of the most promising technologies for reducing flight emissions. By requiring that, from 2041, power-to-liquids (PtL) fuels must source their carbon only from biogenic sources or direct air capture (DAC), the policy could push PtL development into the very land use debates it was designed to avoid. 

Aviation will continue to rely on liquid hydrocarbon fuels for decades. The question is how to reduce its carbon impact. Biofuels offer one route, capturing carbon from the air through plant growth, then releasing it back to the atmosphere on combustion. But biofuels bring complex trade-offs. To protect the climate, we need not only to cut emissions, but also to preserve natural carbon sinks and biodiversity. Expanding biofuels can undermine this goal.

Waste biomass is a better feedstock than purpose-grown oils or starches. Using residues from agriculture and forestry is more land-efficient and avoids direct competition with food. Yet even waste biomass can have hidden impacts. It may come from (and therefore encourage) plantations that have displaced rainforests, or lock in land use that should otherwise be returned to nature. The complexities are endless. 

Carbon source controversy 

The promise of PtL fuels was to offer an alternative without the biofuel land use issues. They combine captured CO2 with green hydrogen to create synthetic hydrocarbons compatible with today’s aircraft. Critically, PtL fuels shift the demand from land to green electricity. Solar and wind power also need land, but it is less, and energy can be generated in places where crops do not grow, relieving pressure on ecosystems. 

The EU recognized this by setting a sub-target for PtL within its broader SAF mandate. This was in recognition that biofuels alone cannot meet demand without environmental harm due to the biofuel land use issues, and that PtL is essential to achieving volume without the same land conversion. 

But concerns soon emerged about circularity in terms of the source of CO2. If PtL fuels reuse fossil-derived CO2 from industrial emitters (or mineral-derived in the case of cement), that carbon will still end up in the atmosphere. It is not circular; some carbon has been used twice but it has still been dug up and released, and the emissions reduction potential is capped. It is lower carbon but not carbon neutral. Some argue this gives emitters an excuse to delay the closure of polluting facilities. 

Unpacking Europe’s new rules 

In response, the EU now requires that, from 2041, PtL fuels must use CO2 captured from biogenic sources. While well intentioned, this policy risks taking PtL back into the very debates about land use and biomass supply that it sought to transcend. While all biogenic carbon is ‘circular’ or theoretically ‘carbon neutral’ in that it recently derives from the air and then returns to it on combustion, once land use is considered, these claims quickly fall down and you realize that no biofuel is a perfect zero emission fuel. 

No developer wants to invest in a CO2 source that will become ineligible. Hence the result is that PtL projects in the EU, and elsewhere who are looking to export to the EU, are now solely chasing biogenic CO2, primarily from ethanol plants due to their scale and purity, though pulp and paper, sugar and biogas plants are also being considered. Whilst it is of course good to try and use all the carbon from biomass, all these sources clearly bind PtL to the same land-constrained carbon cycle that their mother plants contend with. 

This approach completely excludes countries rich in renewables but poor in biomass, such as nations in the Middle East, from playing any role in low carbon aviation fuel. These countries could be ideal locations for producing low-carbon PtL fuels, but the rules close that door. 

DAC dilemmas 

Direct air capture (DAC) is an option, but all chemical engineers know this is an eye wateringly expensive and incredibly energy-intensive one due to the thermodynamics which will never change. Extracting CO2 from air requires vast energy inputs, due to the extreme dilution of CO2 in the atmosphere. While DAC may play a role in the long term, it is not yet a scalable or affordable primary feedstock and in the short term, it is likely to be a reckless use of energy in most locations, particularly given the current size of global emissions. Also, philosophically what distance from a flue gas is air capture considered DAC anyway? As clearly it would be preferred to place your DAC machine with a tiny air gap from a flue gas pipe as the CO2 concentration would be higher? 

The pragmatic answer is to remain open on CO2 sourcing in the near term. What matters is doing what we can to reduce the carbon intensity of aviation fuels now and being open to a variety of sources with different carbon intensities and trade-offs. Not every pathway will be perfect but insisting on narrow definitions too early risks slowing progress. In aviation, where emissions are hard to abate, pragmatism is essential. 

Naturally, PtL developers will favor CO2 sources that offer long-term security, such as cement, steel plants, and natural gas processing, rather than coal power stations that are likely to close. The market will self-correct. But we must give it the flexibility to do so. 

The goal in sight 

The world emits 38 billion tons of CO2 every year. Only a small fraction would be required to decarbonize aviation. With demand for flying set to rise, we cannot afford to block viable pathways out of misplaced rigidity. 

If we force PtL fuels back into the land use debate, we risk losing one of the few scalable tools to reduce aviation’s carbon intensity. Europe’s policymakers must keep their eyes on the goal. Delivering cleaner aviation fuels is hard enough. Let us not make it harder than it needs to be.  

Andrew Symes 

www.oxccu.com 

Andrew is the Co-Founder and CEO of OXCCU, a spinout from Oxford University, specializing in converting waste carbon into fuels, chemicals, and plastics via novel catalysis. OXCCU’s mission is to develop the world’s lowest cost, lowest emission pathways to make SAF, enabling people to continue to fly and use hydrocarbon products but with a reduced climate impact.