Scientists with the United State Department of Agriculture’s (USDA) chief scientific in-house research agency – the Agricultural Research Service (ARS) – have improved the method of producing sustainable aviation fuel (SAF) from soyabean oil, the ARS announced on 22 November.
To date, SAF derived from soyabean oil contained insufficient amounts of “aromatic” compounds, which give density to fuel and help keep engine seals supple and working properly, according to Ken Doll, research chemist with the ARS National Center for Agricultural Utilization Research in Peoria.
For this reason, less SAF derived from soyabean oil could be blended with conventional petroleum-based jet fuels, Doll said.
One current method of making SAF from soyabean oil used the precious metal ruthenium to catalyse reactions that chemically modify the structure and properties of the oils’ unsaturated fatty acids, Doll explained. However, this method generated too few aromatic compounds, he said.
To overcome the problem, Doll and fellow ARS scientists Bryan Moser and Gerhard Knothe replaced ruthenium with iridium as the chief catalyst in a six-step procedure that they devised and patented in November.
In laboratory-scale experiments, use of the method on high oleic-acid soyabean oil had produced jet fuel formulations containing 8% to 35% aromatics - a range compatible with conventional jet fuels and beyond the range ruthenium-based methods could achieve, the ARS said.
Reported in an online issue of the International Journal of Sustainable Engineering, the advance opened the door to increased blending of bio- and conventional jet fuels, according to the ARS. The method also generated little or no naphthalene, which emits soot on combustion.
The researchers were now looking for an industry partner to scale-up the process and evaluate its commercial potential, the ARS said.
Other oilseed crops could also be used in the process, including non-edible sources such as field pennycress, according to the researchers.
“We originally used soyabean oil because of its high quality, affordability and the refinery processes that exist. It's also a commodity that we’ve historically worked with in Peoria,” Doll added. “But any oil that has significant oleic acid levels would work.”