Butanol, a 4-carbon alcohol (butyl alcohol), is generally used as an industrial solvent in products such as lacquers and enamels. However, it can also be blended with gasoline and used as a transportation fuel. Butanol is commonly produced using fossil fuels, but it can also be produced from biomass, in which case it is called biobutanol. Biobutanol is produced from the same feedstocks as ethanol—corn, sugar beets, and other types of biomass. Biobutanol is considered a renewable fuel and qualifies under the Renewable Fuel Standard; the category it falls under depends on the feedstock used to produce it.
There are two Clean Air Act provisions that allow blending of up to 12.5% biobutanol with gasoline, and under the Octamix waiver, with human health effects testing, a 16% biobutanol blend is a legal fuel equivalent to E10. Biobutanol has an ASTM D7862 fuel quality standard for blends up to 12.5% with gasoline. It is important to ensure that biobutanol blended with ethanol/gasoline combinations do not result in an oxygen content exceeding the U.S. Environmental Protection Agency (EPA) limit of 3.7%.
Oak Ridge National Laboratory has researched the compatibility of fueling equipment materials with biobutanol and found that equipment compatible with ethanol blends is compatible with biobutanol. Underwriters Laboratories announced in 2013 that equipment certified under testing subject 87A (for blends above E10) could also retain certification if used with biobutanol. It is anticipated that biobutanol would be distributed by tanker truck and rail, with the potential for transportation in pipelines upon research demonstrating its safety.
Producing biobutanol via fermentation has been possible since the early 1900s, but it is currently more expensive than producing petrochemicals. Modern butanol is produced almost entirely from petroleum. Renewed interest in biobutanol as a sustainable vehicle fuel has spurred technological advances to ferment it. The first biobutanol plants are retrofits of existing corn ethanol plants. Biobutanol companies produce a range of products—solvents/coatings, plastics, fibers, and transportation fuel—to enhance economic performance through diversification. A challenge for biobutanol is that more ethanol than biobutanol can be produced from a bushel of corn.
Biobutanol is an alternative to conventional transportation fuels. The benefits of biobutanol include:
Higher energy content—Biobutanol's energy density is 10%–20% lower than gasoline's energy density. However, biobutanol's energy content is relatively high among gasoline alternatives; for example, the energy density of ethanol (E100) is 60% lower than that of gasoline.
Lower reid vapor pressure—When compared with ethanol, biobutanol has a lower vapor pressure, which means lower volatility and evaporative emissions.
Increased energy security—Biobutanol can be produced domestically from a variety of feedstocks, while creating U.S. jobs.
- Fewer emissions—Carbon dioxide captured by growing feedstocks reduces overall greenhouse gas emissions by balancing carbon dioxide released from burning biobutanol.
Research and Development
The U.S. Department of Agriculture's Agricultural Research Service is studying various aspects of biobutanol production:
- Advanced Conversion Technologies for Sugars and Biofuels
- Improving Biochemical Processes for the Production of Sustainable Fuels and Chemicals
- Mixed Community Bioreactors to Convert Lignocellulosic Feedstocks into the Liquid Biofuel Butanol
Learn more about biobutanol from the links below. The Alternative Fuels Data Center (AFDC) and DOE do not necessarily recommend or endorse these companies (see disclaimer).
- Biobutanol News from the Green Car Congress
- Compatibility Study for Plastic, Elastomeric, and Metallic Fueling Infrastructure Materials Exposed to Aggressive Formulations of Isobutanol-Blended Gasoline
- Impact of Higher Alcohols Blended in Gasoline on Light-Duty Vehicle Exhaust Emissions
- Simulation of the Process for Producing Butanol from Corn Fermentation
- Life-cycle Assessment of Corn-Based Butanol as a Potential Transportation Fuel
- Opportunities in the Industrial Biobased Products Industry
- Production of Butyric Acid and Butanol from Biomass: Final Report
- Emissions and Operability of Gasoline, Ethanol, and Butanol Fuel Blends in Recreational Marine Applications FY 2012
- Emissions and Operability of Gasoline, Ethanol, and Butanol Fuel Blends in Recreational Marine Applications FY 2013
The AFDC also provides a publications search for more information.