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U.S. Department of Energy Energy Efficiency and Renewable Energy

Biobutanol

Butanol, a 4-carbon alcohol (butyl alcohol), is produced from the same feedstocks as ethanol, including corn grain and other biomass. The term biobutanol refers to butanol made from biomass feedstocks. The benefits of biobutanol, when compared with ethanol, are that biobutanol is immiscible in water, has a higher energy content, and has a lower Reid vapor pressure. Under the Renewable Fuel Standard, corn grain butanol meets the renewable fuel 20% greenhouse gas emission reduction threshold.

While there are four isomers of butanol, the most active commercialization work centers on isobutanol for blending with gasoline. Two Clean Air Act provisions allow for blending of up to 12.5% biobutanol by volume with gasoline. Additionally, under a waiver granted by the U.S. Environmental Protection Agency (EPA), a 16% biobutanol blend is a legal fuel equivalent to E10 (10% ethanol, 90% gasoline). Butanol has an ASTM D7862 fuel quality standard for blends up to 12.5% with gasoline.

As of June 2018, the EPA approved up to 16% biobutanol blends. It is important to ensure that biobutanol blended with gasoline does not result in an oxygen content exceeding the EPA limit of 3.7%. The EPA-approved 16% biobutanol level was determined based on the assumption that no other oxygenates (e.g., ethanol) are included in the fuel blend.

Oak Ridge National Laboratory has researched the compatibility of fueling equipment materials with biobutanol and found that equipment compatible with ethanol blends is also compatible with biobutanol. UL Solutions 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.

Production

The first demonstration-scale biobutanol plants were retrofits of existing corn ethanol plants. The fuel is produced through fermentation of corn feedstock and the process is nearly identical to fuel ethanol production from corn. In addition to transportation fuel, biobutanol coproducts include solvents/coatings, plastics, and fibers. Production of these coproducts helps improve economic performance through diversification of product offerings. A challenge for biobutanol is that more ethanol than biobutanol can be produced from a bushel of corn.

Gevo, a biobutanol producer, is focused on converting biobutanol to sustainable aviation fuel via an approved ASTM technology pathway.

Benefits

Biobutanol is an alternative to conventional transportation fuels. The benefits of biobutanol include:

  • Higher energy content—Biobutanol's energy content is relatively high among gasoline alternatives. However, biobutanol's energy density is 10%–20% lower than gasoline's energy density.

  • 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—Fewer emissions are generated with the use of biobutanol compared with petroleum fuels. Carbon dioxide captured by growing feedstocks reduces overall greenhouse gas emissions by balancing carbon dioxide released from burning biobutanol.

  • More transport options—Biobutanol is immiscible with water, meaning that it may be able to be transported in pipelines to reduce transport costs.