PEP Review 2007-1
Published: May 2007
Today’s high oil prices are providing an incentive to develop biofuels in North America. Driven by tax breaks and the 2005 Energy Policy Act, ethanol production has grown significantly in the United States. But other biofuels may be a better alternative than ethanol. Biobutanol has several advantages over ethanol as a fuel component. It generates more miles per gallon and can be shipped through pipelines with gasoline. It does not attract water in the same manner as ethanol making it easier to distribute. Due to these advantages, oil companies have begun developing biobutanol as a fuel.
The first industrial production of n-butanol, around 1912, was based on the discovery of the bacterium Clostridium acetobutylicum Weizmann, which ferments carbohydrates to give mainly acetone and n-butanol. The acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum is one of the oldest known industrial fermentations. It was ranked second only to ethanol fermentation in its scale of production and is one of the largest scale biotechnological processes ever known. However since the peak in the 1950s, industrial ABE fermentation has declined significantly.
In the early 1990s, researchers at the University of Illinois developed a hyper-amylolytic, hyper-butanol producing solventogenic Clostridium designated C. beijerincki BA101 that is efficient in conversion of starch to acetone-butanol. The University of Illinois was issued a patent for the mutant strain in 2002 (US 6,358,717). Laboratory studies have demonstrated use of the organism in a fed-batch/gas stripping system that serves as the basis for this PEP Review.
Our economic evaluation, based on PEP’s concept of the fed-batch n-butanol from corn process, indicates that further technical progress must be made in order for biobutanol to be competitive again either in the solvent or fuel markets. Capital-related items make up a large share of the overall economics. We estimate the total fixed capital to be over $250 million (PEP Cost Index 718) for a grassroots 187 million lb (85,000 T) per year biobutanol plant using corn as the feedstock. Productivity improvements in the fermentation section would enable lower capital requirements. For example, DuPont is currently developing a recombinant bacterium which produces butanol as the sole fermentation product.