DOE: Carbon Emissions of Ethanol vs. Petroleum-Based Fuels

By Valerie Sarisky-Reed, Director of the DOE’s Office of Bioenergy Technologies | June 29, 2022

Biofuels have been proven to emit significantly less greenhouse gases (GHGs) than petroleum-based fuels, and recent scientific studies indicate that net-zero emissions biofuels are not only possible, but achievable.

Corn ethanol and other biofuels are essential in the United States’ transition to a clean energy economy that creates well-paying jobs, increases energy independence, and supports the Biden administration’s climate goals. However, not all biofuels are created equal. The GHG emissions of a biofuel depend on what material it is made from, how it is made, and how it is used — the full biomass life cycle, production and use of biofuel.

As the world’s largest producer and consumer of biofuels, the United States is a critical leader in biofuels science, technology, and policy, and the U.S. Department of Energy (DOE) has spent decades making advancing the science behind life cycle analysis of biofuel emissions (LCA).

Corn Ethanol Life Cycle Emissions Assessments Over Time

Most US biofuels come in the form of ethanol, which is made from cornstarch and then mixed with gasoline. It is estimated that 98% of all gasoline sold in the United States contains 10% ethanol.

In the early 2000s, US energy policy contributed to a significant increase in domestic ethanol production, primarily to increase energy independence. U.S. corn ethanol production grew from about 1.5 billion gallons in 2000 to 16 billion gallons in 2018. Strokes in the early 2000s relied on computer models and assumptions, which estimated that American corn ethanol would produce 20% fewer GHG emissions than gasoline.

Scientific research over the past two decades using improved LCA methods has identified several key trends that were difficult to predict in previous studies, rendering these previous results and predictions inaccurate.

The most recent DOE study, published by Argonne National Laboratory in 2021, found that US corn ethanol has 44-52% lower GHG emissions than gasoline. Argonne National Laboratory is Recognized worldwide as one of the leading experts in this type of LCA research and other credible studies have found similar results.

Argonne analysis found that carbon emissions from U.S. corn ethanol dropped 20% between 2005 and 2019 due to increased corn yields per acre, decreased use of fertilizers and improving ethanol production processes.

Existing Techniques to Reduce Corn Ethanol Emissions

Evidence suggests that additional improvements can further reduce GHG emissions from corn ethanol.

Existing technologies and agricultural practices have the potential to provide further significant improvements in reducing GHG emissions from ethanol ACV from approximately 40% today to over 70% compared to a baseline. petroleum.

Further analysis by Argonne of jet fuel applications concluded that smart farming practices and other existing technologies can reduce ethanol emissions in jet fuel to 153 percent lower than petroleum-based jet fuel. This means that biofuels could be not only net zero, but net-negativecarbon emissions. Since biomass removes carbon dioxide from the atmosphere throughout its life via photosynthesis, net negative emissions biofuels are possible when steps are taken to reduce emissions from biofuel production. These measures can include the capture and sequestration of carbon dioxide emissions that occur during biomass fermentation. Carbon capture and sequestration technology and its application to biorefineries have been demonstrated with DOE funding.

Land use data reflects real impact on LCA

The biggest gap between biofuel LCAs in recent years stems from the idea that the benefits of low-emission fuels are outweighed by the environmental damage caused by their production. Early critics of biofuels argued that rainforests, wetlands, grasslands, and other natural ecosystems (carbon sinks) that remove carbon from the atmosphere would be directly or indirectly destroyed to produce biofuels.

Early LCA studies in the 2000s predicted that US landowners would convert large tracts of forests and wetlands for agricultural production in response to higher demand and prices for corn, which in turn would increase climate emissions. .

The analysis of land use change relies on complex models and the results are strongly influenced by the underlying assumptions that researchers apply. Rigorous scientific studies, debates, and the increased availability of real data from the growing US biofuels industry have resulted in a more accurate understanding of the impacts of biofuel production.

Recent studies based on real data and not on modeling point to initial projections significantly overestimated impacts of land use change.

The future of US biofuels

While studies by Argonne and other respected labs include the most recent scientific data, other scientific papers on biofuel LCA continue to use old and refuted data. Such articles present provocative findings about potential, but avoidable, pitfalls of biofuels, disregarding public and private efforts to ensure that biofuels are produced sustainably at scale.

DOE’s Bioenergy Technology Office (BETO) is committed to ensuring that future domestic biofuel production meets stringent sustainability measures, including those related to significantly reduced GHG emissions. BETO is currently examining strategies to reduce GHG emissions and carbon intensity within the existing corn ethanol industry, including:

    • Implement low-carbon agricultural practices

    • Switch to renewable heat and electricity (eg wind, solar, renewable natural gas or biomass)

    • Develop new measures of productivity and conversion efficiency in biorefinery processes

    • Using or biorefinery CO sequestration2 emissions.

The U.S. Ethanol Industry Supports Surrounding Communities and Rural Partners

The U.S. ethanol industry has enough capacity to produce more than 17 billion gallons of ethanol and reduce GHG emissions by approximately 42.7 million metric tons (CO2-eq) per year, or about 2% of total US transportation emissions. The United States has more than 200 ethanol plants that support nearly 70,000 jobs, many of them in rural areas.

Since biomass cannot be transported economically over long distances, biofuel production facilities depend on raw materials produced within a short radius of the refinery. Owners and operators of biorefineries have a natural incentive to ensure long-term sustainability through the raw materials they use, the way they are grown and replenished, and the way their projects support and are supported by communities. surrounding. The production of low-GHG liquid transportation fuel can create jobs in rural economies and help decarbonize remote communities without short-term access to electric vehicle charging stations and therefore dependent on existing refueling infrastructure.

Investing in low GHG fuels will help address environmental justice issues in rural and underserved communities to ensure they are not left behind in the transition to clean energy.

BETO research, development and demonstration of biofuel technologies for further reduction of GHG emissions

BETO funds the research, development and demonstration of next-generation biorefineries that will take advantage of a variety of sustainable sources of biomass feedstock and waste. These include:

    • Agricultural residues (for example, corn stalks)

    • Forest residues (for example, residues from logging and forest thinning)

    • Dedicated energy crops (eg switchgrass, miscanthus, energy cane, sweet sorghum, high biomass sorghum, hybrid poplars and shrub willows)

    •Algae

    • Reusable waste streams and carbon sources (eg non-recyclable portions of municipal solid waste; sewage treatment sludge and manure sludge; food waste; and carbon dioxide and industrial waste gases) .

These abundant US-based biomass and waste resources can offer the sustainable feedstocks needed to support a growing low-carbon biofuels industry. These same renewable feedstocks can achieve over 70% reduction in GHG emissions for a variety of end-use fuels.

The transition to a sustainable net-zero GHG emissions economy in America will only be possible by embracing clean energy provided by biofuels. With science as our guide, the DOE and its partners have spent decades researching, studying, and testing ethanol and ethanol technologies, as well as second-generation biofuels to better understand the potential of this fuel source. essential and sustainable energy.