Switching catalyst boosts aromatics compounds in SAF production from soybean oil
Scientists with the Agricultural Research Service in Peoria, Illinois, have developed a way to make a better sustainable aviation fuel (SAF) from soybean oil.
Fatty acids from soybean oil can be turned into an array of industrial products normally made from petroleum, including fuel, ink and paints. One appeal of plant-based products is that they recycle carbon found in the atmosphere. This makes plants a far more renewable resource than petroleum and other fossil fuels, which add carbon to the atmosphere as they're extracted from the earth and used.
However, soy-based SAF developed to date contain insufficient amounts of aromatic compounds, which impart desirable density to fuel and help keep jet engine seals supple and working properly. The current shortcoming of aromatic levels in soy SAF means less of it can be blended with conventional jet fuels derived from petroleum, explained Ken Doll, a research chemist with the ARS National Center for Agricultural Utilization Research in Peoria.
Blends using biofuels are one of the ways the aviation industry is working to reduce its carbon footprint, or total emissions of greenhouse gases, particularly carbon dioxide (which amounted to 905 million tons in 2018).
One approach to making soy-based SAF relies on the use of a precious metal called ruthenium to catalyze reactions that chemically modify the structure and properties of the oil’s unsaturated fatty acids. The problem with this approach is that it generates too few aromatic compounds, noted Doll, with the ARS center's Bio-oils Research Unit.
To get around the problem, he 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 received a patent in November.
In laboratory-scale experiments, use of the approach on high oleic-acid soy oil produced jet fuel formulations containing 8 to 35 percent aromatics—a range compatible with conventional jet fuels and beyond what ruthenium-based methods can achieve.
The advance, which the team recently reported in an online issue of the International Journal of Sustainable Engineering, opens the door to increased blending of biobased and conventional jet fuels as an emissions-cutting measure. The method also generates little or no naphthalene, a jet fuel component that emits soot upon combustion.
The researchers are now looking for an industry partner to scale-up the process and evaluate its commercial potential further.
Their research also supports a broader effort at the ARS center in Peoria to develop new, value-added uses for agricultural commodities or their waste byproducts, as well as to create sustainable new methods for processing them. Ideally, for example, the iridium used to create soy-based SAF could be replaced or combined with an earth-abundant catalyst like iron to drive down the cost, Doll said.
Other oilseed crops besides soy could also be used, including nonedible sources such as field pennycress. “We originally used soy oil because of its high quality, affordability and the refinery processes that exist,” Doll added. “It’s also a commodity that we’ve historically worked with in Peoria. But any oil that has significant oleic acid levels would work.”
The Peoria team's efforts are also reflective of the USDA’s participation in the Sustainable Aviation Fuels Grand Challenge together with other federal agencies and stakeholder groups. The challenge is a multifaceted government-wide commitment to enabling the production of 35 billion gallons of sustainable aviation fuel per year by 2050, using homegrown and other renewable sources.