Advanced BioFuels USA

by Jeff Overton (Environmental and Energy Study Institute)  … Aviation is a difficult sector to decarbonize. The enormous energy required to fly a heavy aircraft long distances takes an energy dense power source that liquid hydrocarbon fuel provides. Battery technology for electric flight is improving. However, batteries currently do not have an energy density anywhere close to liquid fuel and would be too heavy for large aircraft over long distances. Hydrogen (H2) is a potential liquid fuel that generates only water vapor in combustion and very small amounts of nitrous oxides. Shifting to H2 as a fuel source presents a significant set of challenges in production, storage and infrastructure, aircraft configuration and engine modification requirements. All electric- or hydrogen-powered flight for large aircraft and long distances could be decades away.

The strategy with the most promise for substantially reducing the sector’s carbon footprint in the near and medium term is expanding the use of sustainable aviation fuel (SAF). SAF is an alternative jet fuel made from renewable biomass or waste-based feedstock that has a lower life-cycle carbon intensity than conventional petroleum-based fuel. SAF can be made from a variety of feedstock such as oil seed plants and energy grasses; agricultural and forestry residue; organic municipal solid waste; fats, oils, and greases from cooking waste and meat production; algae; and industrial carbon monoxide waste gas.

…

Another type of sustainable jet fuel is e-SAF or Power to Liquid (PtL). PtL is produced by combining hydrogen, which can be split off from water (it’s the “H” in H₂O) using renewable electricity in a process called electrolysis, with carbon extracted from the atmosphere or from industrial waste gas. Barriers to wider use of this technology are the cost of PtL, which is significantly higher than the cost of other types of SAF, and the availability of renewable electricity for the electrolysis.

…

There are currently seven SAF production processes (pathways) approved as safe for use in blended form by civilian jet aircraft.

…

Life-cycle CO2 emissions from “neat” (unblended) SAF can be up to 80 percent lower than those from conventional petroleum-based fuel.

…

SAF also generates fewer conventional pollutants that contribute to local air quality concerns around airports. It emits fewer sulfur oxides and particulates, less carbon monoxide and fewer unburned hydrocarbons. With fewer particulates in aircraft exhaust, contrail formation is diminished.

…

Challenges of Sustainable Aviation Fuels

…  SAF is much more expensive than fossil-based fuel, costing generally at least four or five times more than conventional jet fuel.

…

Fats, oils, and greases (FOG) are the feedstocks most in use today for SAF but are in limited supply. A diverse set of feedstocks is required for a shift from conventional jet fuel. More than one billion dry tons of biomass is potentially available annually in the conterminous United States as feedstock for bioenergy and chemical products, enough to exceed projected U.S. domestic aviation fuel demand.

SAF competes with renewable diesel (RD)—used in road transport—for feedstock resources and production capacity. RD benefits from favorable tax policy, making its production more profitable; it dwarfs SAF output nationally.   READ MORE