A common farm weed could make a jet fuel with fewer production-related environmental impacts than other biofuels, according to a new lifecycle study by researchers at The Ohio State University. Growing the weed, pennycress—often called stinkweed—as a crop requires less fertilizer and fewer pesticides than other plants that can be used to make renewable jet fuel, according to the study.

The objective of this study was to evaluate the energy requirement and environmental impacts of hydroprocessed renewable jet fuel (HRJ) production from pennycress. The system boundary included pennycress production, logistics, oil extraction and conversion to HRJ, wastewater treatment, and electricity and steam generation. Energy allocation method was used for the analysis. The functional unit was considered to be one GJ of HRJ, and the biorefinery size was considered to be 18.9 million l/yr (5 million gal/yr) HRJ. Energy use efficiency of pennycress-based HRJ production was estimated to be 3.9–5.5 (90% central range), which was higher than that of HRJ from other oilseeds, such as canola. Global warming potential of pennycress-based HRJ (35–49 kgCO₂eq/GJ of HRJ (90% central range)) was also lower than those of HRJ from similar oilseeds and the commercial jet fuel baseline.

—Mousavi-Avval and Shah

Pennycress also requires fewer farm operations, such as soil tilling, than other potential biofuel crops, reducing the associated environmental costs, include carbon dioxide emissions and other emissions.

Environmental impacts could be further mitigated through farm management techniques that keep fertilizer on fields, rather than allowing it to run off into nearby watersheds, the study suggests. Such techniques can add to the financial cost of growing crops, but reduce their environmental footprints.

The study was published recently in the journal Applied Energy.

For this study, the researchers estimated the environmental impacts of growing pennycress, transporting it to a biorefinery and converting it to a usable jet fuel. They also accounted for the environmental costs of burning leftover byproducts of refining the pennycress seed into fuel.

Those environmental costs include fertilizer and pesticide use, water consumption and the energy required to harvest and transport pennycress seeds from a farm to a biorefinery and process them into usable fuel.

The researchers built computer models to determine how much total energy it would take to produce jet fuel from pennycress seeds and compared those estimates with the energy needed for producing biofuels from other crops. The data for the models came from existing studies about biofuel production.

Their models showed that it took about half as much energy to produce jet fuel from pennycress as it did to produce jet fuel from canola or sunflowers, two other potential bio-jet fuel crops. Pennycress oil production used about a third as much energy as soybean oil production, the researchers found, and the energy needed for turning pennycress into jet fuel was about the same as that used to produce fuel from the flowering plant camelina, another biofuel crop.

Pennycress also makes an appealing alternative jet fuel because of its growing season. It is a winter cover crop that can be grown between corn season and soybean season, giving the same body of farmland an extra production cycle each year.

Pennycress can be planted when corn is still standing in the field, before the corn harvest. And it can be harvested before the soybean crops are planted. 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.

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. If we could improve those areas, we could make production more energy-efficient and substantially lower the costs and environmental impacts.

—Ajay Shah, senior author

This work was supported by funding from the US Department of Energy.

Resources

• Seyed Hashem Mousavi-Avval, Ajay Shah (2021) “Life cycle energy and environmental impacts of hydroprocessed renewable jet fuel production from pennycress,” Applied Energy, doi: 10.1016/j.apenergy.2021.117098