Stinkweed could make for greener renewable jet fuel

Pennycress, often referred to as stinkweed, is a common weed throughout Eurasia and North America. In the past 20 years, there has been some interest in harnessing it as a potential renewable fuel crop rather than just treating it as a weed, as the high erucic acid content of its seeds could make it suitable as a jet fuel.

“Reducing greenhouse gas emissions from air travel will mean not just incremental changes, but a fundamental change in how we have been producing fuel and where that fuel comes from,” said Professor Ajay Shah, senior author of the Ohio State University study. “And what we found is that pennycress might make a very good alternative fuel, especially when you consider the environmental costs of producing it.”

Growing pennycress as a crop requires less fertiliser and fewer pesticides than other plants that can be used to make renewable jet fuel, the researchers concluded. It also requires fewer farm operations, such as soil tilling, than other potential biofuel crops, reducing associated environmental costs such as carbon dioxide emissions and other pollutants. Its environmental impact could be mitigated even further through adapting farm management to maintain fertiliser on fields, rather than allowing it to run off into nearby bodies of water.

The researchers reached these conclusions by estimating the impacts of growing, transporting, and converting pennycress. They also accounted for the environmental costs of burning leftover by-products of the refinement process; these costs account for fertiliser and pesticide use, water consumption, and the energy required to harvest and transport pennycress seeds.

They used computer models to determine the total energy required to produce jet fuel from pennycress seeds, and compared these estimates with the energy required to produce biofuels from other crops (using data from existing studies on biofuel production). The models showed that it took approximately half as much energy to produce jet fuel from pennycress as it did to produce it from canola or sunflowers and approximately a third as much as from soybeans. The energy required was similar to that used to produce fuel from the flowering plant camelina.

Another attraction of pennycress, the researchers said, is that it is a winter cover crop that can be grown between seasons for corn and soybean, providing an extra production cycle for the same body of farmland. “The bottom line is it can be used as a cover crop, it doesn’t divert any agricultural production land, and it has suitable properties for renewable jet fuel production,” said Shah.

Shah explained that renewable jet fuels are not financially competitive with fossil fuel-based fuels at present. However, being able to quantify the environmental impacts of biofuels will help inform farmers and policymakers as they play their part in limiting carbon emissions in line with Paris Agreement commitments.

“When it comes to pennycress, production and logistics are the big contributors to both the environmental impacts and the costs, and those are the challenge areas; they have to be streamlined and solved to make it more efficient,” he continued. “If we could improve those areas, we could make production more energy-efficient and substantially lower the costs and environmental impacts.”