Jet Fuel from Air, at the Wrong Chain Length

Fischer-Tropsch (FT) synthesis from biomass gasification or power-to-liquid (CO2+H2) is a leading pathway for sustainable aviation fuel (SAF). But the Anderson-Schulz-Flory (ASF) product distribution — a fundamental constraint of FT chemistry — limits the straight-run jet fuel fraction (C9–C16) to ~40% maximum with conventional Fe or Co catalysts. The remaining 60% is lighter and heavier hydrocarbons requiring energy-intensive upgrading. Bifunctional catalysts that break the ASF distribution face a certification bottleneck independent of technical performance.

Aviation cannot electrify for long-haul flights and has no zero-carbon fuel alternative besides SAF and hydrogen (which requires entirely new aircraft). SAF from FT currently accounts for <0.1% of aviation fuel; existing and planned projects will meet only 2–4% of demand by 2030. Improving jet-range selectivity beyond the ASF limit would dramatically reduce the energy penalty and cost of FT-SAF, making it competitive with fossil jet fuel.

Bifunctional catalysts combining FT metals with zeolite cracking show promise for narrowing product distribution toward jet-range hydrocarbons. Promoter addition, reactor design modifications (slurry vs. fixed-bed), and operating condition optimization have been explored. However, improved jet selectivity often comes at the cost of catalyst lifetime or conversion rate. ASTM D7566 Annex 1 currently approves only Fe and Co catalysts for certified SAF — bifunctional catalysts that break the ASF distribution have not yet received independent ASTM approval, creating a certification bottleneck. Competing feedstock demands from road transport biofuels further constrain biomass supply for aviation.

FT catalyst systems achieving >60% jet-range selectivity with >5,000-hour stability. An ASTM certification pathway for non-conventional catalyst chemistries — currently the approval process is not designed to evaluate novel catalyst types. Process designs that integrate upgrading of non-jet fractions without canceling the carbon benefit.

A team could screen bifunctional catalyst formulations (Fe or Co + zeolite) in a bench-scale FT reactor, measuring product distribution and comparing against the ASF theoretical limit. Alternatively, a team could model the full lifecycle carbon balance of FT-SAF with various selectivity levels to quantify when upgrading energy cancels the climate benefit. Catalysis, chemical engineering, and lifecycle assessment skills apply.