Bioenergy

Why Isn’t Butanol More Prevalent?

I was wondering if butanol is a more efficient fuel than ethanol and, if so, why don’t we hear more about it? — Robert M., Kansas City, MO

Butanol is a four-carbon alcohol. Alcohols also include methanol (1-carbon), ethanol (2-carbon) and propanol (3-carbon). Butanol is used primarily as an industrial solvent. The worldwide market is about 350 million gallons per year with the U.S. market accounting for about 220 million gallons per year. Butanol currently sells for about $3.70 per gallon in bulk (barge). Butanol can also be a replacement for gasoline as a fuel without major engine modifications and can be shipped through existing fuel pipelines. Butanol has a high energy content (110,000 Btu per gallon for butanol vs. 84,000 Btu per gallon for ethanol). Gasoline contains about 115,000 Btu’s per gallon. Butanol is six times less “evaporative” than ethanol and 13.5 times less evaporative than gasoline, making it safer to use as an oxygenate in Arizona, California and other states, thereby eliminating the need for very special blends during the summer and winter months. Even the U.S. Department of Energy funded a study of butanol, under a federal DOE/STTR grant from the Department of Energy through the Small Business program (DE-F-G02-00ER86106), in association with Dr. S.T. Yang of the Ohio State University. There has been little to no effort to promote butanol as an alternate fuel because of historically low yields and low concentrations of butanol compared to those of ethanol; that is, for each bushel of corn you would garner (1.3) gallons of butanol (0.7) gallons of acetone and (0.13) gallons of ethanol with concentrations of 1-2%. Butanol is presently manufactured from petroleum. Historically (early 1900s – 1950s) it was manufactured from corn and molasses in a fermentation process that also produced acetone and ethanol known as an ABE (acetone, butanol, ethanol) fermentation. However, as demand for butanol increased, production by fermentation declined mainly because the price of petroleum dropped below that of sugar when the U.S. lost its low-cost supply from Cuba around 1954. If you compared ABE yield to that of the yeast ethanol fermentation process, the yeast process yields 2.5 gallons of ethanol from a bushel of corn; with concentrations of 10-15% it becomes very clear why ethanol is considered a better alternative fuel source over butanol. One company, Environmental Energy Inc. (EEI) has developed and patented technology that they believe overcomes the limitations that have to date kept the cost of butanol production from corn and other forms biomass high. EEI claims they can produce 2.5 gallons of butanol from corn with no acetone or ethanol, whereas most other processes have not been able to achieve better than 1.3 to 1.9 gallons of butanol per bushel and still utilize an ABE process. Some experts in the automotive industry have been publicly praising butanol, so don’t count it out by any means, as new flex-fueled vehicles come to market. — Scott Sklar Scott Sklar is President of The Stella Group in Washington, DC, a distributed energy marketing and policy firm. Scott, co-author of “A Consumer Guide to Solar Energy,” uses solar technologies for heating and power at his home in Virginia. Have a question? Please contact Scott regarding new products, technologies or experiences for future Q&A columns.