A collaboration of US researchers has pioneered a 100% sustainable aviation fuel using an underutilised natural resource known as lignin.
Lignin comprises the rigid parts of a plant’s cell walls, and although parts of plants have previously been employed to design biofuels, lignin has been overlooked due to the challenges of chemically breaking down lignin and converting it into useful products.
Experts now appear to have overcome these difficulties, developing an aviation fuel from lignin that is 100% sustainable that may enable the airline industry to cut its carbon emissions significantly.
The full study, titled “Continuous Hydrodeoxygenation of Lignin to Jet-Range Aromatic Hydrocarbons,” can be found here. The research was funded by the US Department of Energy’s Bioenergy Technologies Office and Center for Bioenergy Innovation.
Sky high aviation sector emissions
To combat the effects of climate change, the airline industry has pledged to drastically reduce its carbon emission, meaning the need for sustainable aviation fuel has never been more paramount. In 2019 alone, airlines worldwide burned through 106 billion gallons of jet fuel, a figure that is forecasted to more than double by 2050.
With targets of accomplishing carbon-neutrality during the same time period, innovating novel sustainable aviation fuel solutions with high blend limits with conventional fuel will be key to achieving net zero goals.
Lignin-powered aviation fuel
Jet fuel is comprised of a concoction of various hydrocarbon molecules, such as aromatics and cycloalkanes. However, current technologies cannot produce these components in a manner that qualifies them as 100% sustainable aviation fuel. Because of this, sustainable aviation fuel blendstocks are mixed with traditional hydrocarbon fuels.
Lignin is the most substantial source of renewable aromatics in nature and could hold the key to developing a complete bio-based jet fuel. The study illuminates the ability of a lignin pathway to complement existing and other developing pathways, most notably, a pathway that allows sustainable aviation fuel to have fuel system compatibility at higher blend ratios.
Due to its recalcitrance, lignin is usually burned for heat and power and is predominantly used in low-value applications. Earlier studies developed lignin oils with high oxygen contents ranging between 27% and 34%; however, for them to be used as jet fuel, the oxygen content would need to be reduced to less than half a per cent.
Scientists have explored other methods to reduce the oxygen content, but the catalysts required used expensive noble metals and achieved low yields. In the current study, the team employed a method using earth-abundant molybdenum carbide as the catalyst in a continuous process, producing an oxygen content of around 1%. Although further refinement is needed, a true, 100% aviation fuel could soon be on the horizon.