by Emil Morhardt
Butanol is a four-carbon alcohol, next in size after 1-C methanol (wood alcohol), 2-C ethanol (drinking alcohol), and 3-C propanol (rubbing alcohol), so it shouldn’t come as any surprise that yeast ought to be able to synthesize it out of sugar. And it burns like the other alcohols mentioned, so it is potentially a usable liquid fuel that could be mixed with gasoline (like ethanol, to increase it’s non-fossil-fuel content), processed into other types of fuel, or used as commercial feedstock to make bio-based commercial plastics such as the PET (polyethylene terephthalate) used to make beverage bottles. Gevo, Inc., a company based in Englewood, Colorado but with it’s only [troubled] production facility in Luverne, Minnesota, seems to be gradually overcoming myriad difficulties in commercializing biomass-based isobutanol, and is beginning to license its proprietary genetically-modified yeast, which produce more isobutanol than conventional ethanol-producing commercial varieties. Gevo hopes that these yeast will feel right at home in existing ethanol-production facilities (such as the Luverne plant, where they didn’t do so well initially), and that all Gevo will have to do to get isobutanol out is to bolt on a module that separates the isobutanol from the water in which the yeast are living.
According to Brett Lund, the chief licensing officer at Gevo (as noted in the article cited below in Biomass Magazine) the clever way they do this is to create a vacuum above the yeast/water/butanol broth, which volatilizes the butanol which is then condensed out. This is similar to the distillation concept used with ethanol, but doesn’t require boiling the broth which is expensive and kills the yeast.
Gevo’s yeast engineering appears to allow them to produce yeast specialized to ferment optimally whatever kind of sugars are available (for example they have just signed a licensing agreement with Highlands EnviroFuels (chemengonline.com) which already has a syrup mill processing locally grown sugar cane and sweet sorghum, onto the back end of which they propose to “bolt” an isobutanol plant. Isobutanol is not as soluable in water as ethanol so it is considered a good potential marine fuel, apparently satisfying the requirements of the Coast Guard, and has been demonstrated to be convertible into a fuel suitable for powering USAF fighter jets.