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May 15, 2009 (Vol. 29, No. 10)

Forging Isobutanol with Modified Microbes

Gevo Is Developing Microbial Fermentation Methods for Renewable Fuel Production

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    Plant biomass is converted into purified isobutanol and animal feed using Gevo’s biocatalysts and GIFT™ processing technology.

    Ethanol is not the only alcoholic fuel that can be made from renewable feedstocks through microbial fermentation. Gevo is producing higher-chain alcohols such as isobutanol, which currently come from oil.

    “We found a way to produce isobutanol at 50 percent of the cost of petrochemical processes, and it’s 99.5 percent pure,” says Patrick Gruber, Ph.D., Gevo’s CEO. The company’s microbial fermentation method for making isobutanol can be readily adapted, he says, to equipment and infrastructures at existing ethanol plants, where the drop in oil prices has diminished ethanol output.

    The microbial method for making isobutanol was developed in the laboratory of James Liao, Ph.D., a professor of chemical and biomolecular engineering at the University of California, Los Angeles. Gevo holds an exclusive license to the technology, which genetically alters E. coli to generate several higher-chain alcohols from glucose, including isobutanol, 1-butanol, 2-methyl-1-butanol, and 2-phenylethanol. Dr. Liao metabolically engineered E. coli’s amino acid biosynthetic pathway to divert its 2-keto acid intermediates for alcohol synthesis.

    Bacteria and yeast naturally ferment sugars to ethanol, but isobutanol had never been produced from a renewable source with yields high enough to be a viable alternative to gasoline.

    “We use biotechnology to take the variability out of Mother Nature and make pure products selectively,” adds Dr. Gruber.

    Gevo started in Pasadena, CA, in 2005, to pursue the conversion of waste methane into methanol, based on technology developed at the California Institute of Technology. Although the project proved commercially impractical, knowledge gained about the molecular biology and energy pathways in microorganisms is now being applied to making 3-, 4-, and 5-carbon alcohols. Gevo moved to the Denver area in February 2007, attracted by skilled workers and lower operating costs, and to be closer to feedstocks and ethanol facilities in the Midwest.

  • Customers

    In order to determine what alcohols to pursue commercially, Gevo interviewed experts at oil refineries about their needs.

    “They told us they wanted products with lower volatility than ethanol,” explains Dr. Gruber, “because air quality standards are getting tighter and tighter under the Clean Air Act.” They also wanted products with high octane ratings and the energy value of gasoline. Gevo scientists evaluated these desired characteristics in light of their skills at making renewable biofuels. “Isobutanol was the best fit, and it has a higher octane compared to other butanols.”

    Ethanol made from corn has limitations as a biofuel. It’s less efficient than gasoline and must be mixed with gasoline as a transportation fuel. It also absorbs water from the environment, making it corrosive to storage tanks and distribution pipes. Isobutanol, in contrast, is less volatile and corrosive, does not readily absorb water, and has an octane rating similar to gasoline. Moreover, Gevo’s microbial platform is based on simple chemistry and avoids the complex separations of mixtures required in the petrochemical industry, Dr. Gruber reports.

    Gevo plans to produce isobutanol that will be blended into gasoline. Additionally,   isobutanol is a good feedstock for higher value chemicals. Isobutanol can be dehydrated in a simple chemical process to make isobutylene, an ingredient for plastics used in flatscreen televisions and pop bottles, as well as jet and diesel fuels.

    The isobutanol market is completely different from the ethanol market, notes Dr. Gruber. Isobutanol is a higher value product than ethanol, and it travels down a different distribution channel with a higher price point.

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