Co-processing bio feedstocks in conventional oil refineries to make sustainable aviation fuel (SAF) has reached commercial scale, but further growth will be challenging and costly, attendees heard at the IATA World Sustainability Symposium in Brussels this week.
Around one third of Europe's oil refineries co-process feedstocks like used cooking oil (UCO) alongside crude to make a fraction of sustainable fuels for European mandates, FuelsEurope fuels executive Sebastian Hirsz said.
This reflects modest early SAF demand, and rising mandates strengthen the case for investing in more capacity, he said.
Co-processing ratios are capped by fuel standards such as ASTM, but pending more testing these limits could be eased over time, he said.
Fragmented policy on feedstocks is a barrier because EU member states have written different co-processing rules into national law, so a feedstock allowed in one country may be blocked elsewhere, Hirsz said. The rules need "tidying up" to unlock further investment, he said.
Co-processing also faces technical challenges, said Spanish refiner Moeve's senior vice president for strategy and international growth Rik Sneep. Refineries can typically cope with 5-10pc bio feedstock without problems, but blending higher ratios adds acidity that requires upgrades to the hydrocracker or metallurgy adjustments, he said.
The business case varies by refinery. Upgrading older or challenging brownfield sites can see costs spiral to "two, three, or four hundred million," Sneep said. Some refineries will be "really well placed to make upgrades at relatively low cost," but for others it may be more economical to build greenfield biorefineries, he said.
Refining bio feedstocks introduce more oxygen in the system and need significantly more hydrogen, which adds costs, Sneep said. Feedstocks like used cooking oil (UCO) are collected from diverse suppliers, meaning they are inherently inconsistent and challenging to work with, he said.
Refineries may employ other techniques to trim lifecycle emissions of their fuels, such as co-processing a share of synthetic e-crude made with renewable hydrogen and captured CO2, said FuelsEurope's Hirsz. Using renewable hydrogen in refineries and biorefineries is also a major lever to trim the lifecycle emissions of SAF, he said.
This could apply to co-processed SAF or neat biofuel SAF. The EU's SAF mandate works on a volume basis and does little to encourage SAF producers to cut emissions beyond meeting the minimum eligibility.
Companies disagree about how best to incentivise renewable hydrogen in SAF. One option is categorising SAF made with renewable hydrogen as synthetic SAF (e-SAF). Refiners have urged the EU to allow this, but pure-play e-SAF companies say it would undermine their projects.
The European Commission is analysing this 'e-HEFA route' but has reached no decision, said EU mobility and transport department head of aviation policy Eddy Liegeois. Such a policy would grow the hydrogen industry and help scale e-SAF, and help lower biofuels lifecycle emissions, but commission is wary of jeopardising "genuine" e-SAF projects, he said.
