A new lifecycle analysis by researchers at Argonne National Laboratory has found that the carbon intensity of corn ethanol has decreased 23%—from 58 to 45 gCO₂e/MJ—from 2005 to 2019. Their open-access paper is published in the journal Biofuels, Bioproducts and Biorefining.

Carbon intensity (gCO₂e/MJ undenatured ethanol) of corn ethanol without LUC for 2005–2019. Lee et al.

The researchers attributed the significant decrease to a several factors:

• Corn grain yield has increased continuously, reaching 168 bushels/acre (10.5 metric tons/ha, a 15% increase) while fertilizer inputs per acre have remained constant, resulting in decreased intensities of fertilizer inputs (e.g., 7% and 18% reduction in nitrogen and potash use per bushel of corn grain harvested, respectively).

• A 6.5% increase in ethanol yield, from 2.70 to 2.86 gal/bushel corn (0.402 to 0.427 L kg⁻¹ corn), and a 24% reduction in ethanol plant energy use, from 32,000 to 25,000 Btu/gal ethanol (9.0 to 6.9 MJ L⁻¹ ethanol) have also helped reduce the CI.

From the reduction in corn ethanol GHG emission intensity and ethanol volume expansion, we estimate that the ethanol industry has achieved an additional 140 MMT cumulative GHG emission reduction from 2005 to 2019. The ethanol produced in our 15 years has been introduced to the transportation sector to displace petroleum gasoline. With the displacement, on the LCA basis, corn ethanol has helped the US transportation sector reduce GHG emissions by 544 MMT over the period.

Additional measures exist to reduce corn ethanol GHG emissions further. In the farming stage, sustainable farming practices such as no-till and cover crops can help reduce fertilizer inputs and increase soil organic carbon content. In ethanol biorefineries, fermentation CO₂ can be captured and sequestered, and fossil natural gas can be replaced with renewable natural gas and biomass gasification. Biofuels, including corn ethanol, can play a critical role in the US desire for deep de-carbonization of its economy.

—Lee et al.

The Argonne team used Argonne’s GREET model for this study. Argonne developed GREET (the Greenhouse gases, Regulated Emissions, and Energy use in Technologies) model, a one-of-a-kind LCA analytical tool that simulates the energy use and emissions output of various vehicle and fuel combinations.

The work was funded by DOE’s Vehicle Technologies Office in the Office of Energy Efficiency and Renewable Energy.

Resources

• Lee, U., Kwon, H., Wu, M. and Wang, M. (2021), “Retrospective analysis of the U.S. corn ethanol industry for 2005–2019: implications for greenhouse gas emission reductions.” Biofuels, Bioprod. Bioref. doi: 10.1002/bbb.2225