Aviation biofuels hold many promises, perhaps the most important being their ability to yield reductions in greenhouse gases emitted by aircraft in flight. Still, airlines will be willing to transition to sustainable fuels only if there is a financial case to do so.
Fuel costs are a significant portion of an airline’s overall operating costs — often, they’re the greatest portion. Given that airlines typically generate razor-thin profit margins even in good years — and incur substantial losses in bad years — fuel for the airlines must be competitively priced and reliably provided.
Currently, biofuels for aviation are scarce and expensive. Yet as more supply comes on line, prices will start to fall. The key milestone will be the day when the cost of a gallon of biofuel reaches parity with the cost of using petroleum-fuel-based jet-A.
How do we get there? The science behind biofuel production is a fascinating study of human ingenuity. Researchers are employing surprisingly similar techniques to those used to create petroleum-based jet fuel, but they’re doing it completely with biomass. This can include everything from microscopic algae to recycled cooking oil. Just about anything that can be transformed into biofuel without impacting the world’s food supply is being considered as a potential fuel source.
Once the feedstock for biofuel has been harvested, it must be processed. Two processing techniques have been approved so far — biomass to liquid (BtL) and hydroprocessed esters and fatty acids (HEFA). In the HEFA process, biomass such as algae, jatropha or camelina are pressed to extract the oils inside. These plant oils are then refined into jet fuel, with the remaining plant material converted for other uses, such as for fertilizer or animal feed. The BtL process, meanwhile, breaks down the feedstock through gasification, a process during which the biomass is heated to extremely high temperature, cracking the molecules and producing gases. The gas is converted to liquid fuel through the Fischer-Tropsch process.
Two other promising biofuel production techniques have emerged recently. The first is called the alcohol-to-jet process, which (as the name suggests) relies on fermentation of cellulose and sugars to yield fuel. The second is based on pyrolysis of biomass, which applies heat to raw materials to produce an oily substance that can be refined into jet fuel. Both processes are attracting interest among biofuels researchers because they yield fuels that are potentially cheaper to make and can reuse waste that would otherwise produce greenhouse gas during decomposition.
