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David Bradley ISSUE #72
January 2008
Lars Angenent
Butanol Biofuel Bandwagon

In 2006, chemical manufacturer DuPont and oil company BP announced a collaboration with British Sugar to convert sugar beets into butanol as a gasoline-blending additive in the UK. Now, it seems others are seeing the potential benefits of jumping aboard the butanol bandwagon. A research team at Washington University in St. Louis is, for instance, developing new techniques for making biofuel using butanol instead of the inferior alcohol ethanol.

Butanol is closely related chemically to ethanol; it has, however, two extra carbon atoms and their attendant hydrogens and so has a higher energy value. In terms of storage and handling, it is less corrosive than ethanol and has several other advantages. More to the point, it can be made from woody and plant biomass, straw, agricultural residues, corn fiber and husks, and sugar beets, most of which contain a large proportion of cellulose and some lignin.

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Assistant professor of energy, environmental and chemical engineering at WUSTL, Lars Angenent, is working with pre-treated corn fiber, a byproduct of the corn-to-ethanol production process with collaborators at the United States Department of Agricultural (USDA) research facility in Peoria, Illinois. For their part, USDA researchers Bruce Dien and Michael Cotta have developed and employed physical and chemical techniques that make the otherwise hard to digest ligno-cellulosic material into a more amenable material prior to digestion.

Angenent and his colleagues then place the ligno-cellulosic biomass into digesters that are comprised of a selected mixed culture of thousands of different microbes. These microbes ferment the biomass, analogously to the way yeast ferment sugar into ethanol, but the product of the digester process is butyric acid. Butyric acid is the carboxylic acid precursor to butanol. A final fermentation process is then applied to this compound in Peoria by colleague Nasib Qureshi, which converts the butyric acid into butanol itself.

"The thrust of my lab is the use of mixed cultures," explains Angenent. "The advantage of mixed cultures is that it can take just about any waste material, and through our manipulations, convert it into something valuable." He adds that by altering the acidity, or pH, of the culture, it is possible to produce methane gas, this is produced at neutral pH. At lower pH (more acidic), butyric acid, or more properly butyrate ions are produced ready for conversion into butanol by biochemical removal of an oxygen atom.

"Ligno-cellulosic biomass is plentiful, renewable, and a good way to deal with wastes," adds Angenent. "By using it, we open the door for better economic opportunities for crop producers and rural communities. And because this kind of biomass is carbon-neutral, we don't worry about carbon dioxide being released into the atmosphere."