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Corporate Profile : May 15, 2009 (Vol. 29, No. 10)

Forging Isobutanol with Modified Microbes

Gevo Is Developing Microbial Fermentation Methods for Renewable Fuel Production
  • Carol Potera

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.

Joint Ventures

To retrofit existing ethanol facilities to manufacture isobutanol, the company designed Gevo’s Integrated Fermentation Technology (GIFT™). The main alteration at ethanol plants involves the addition of separation equipment to purify butanol from the fermentation broth.

Gevo is working with ICM, an engineering firm, to retrofit an ethanol facility in St. Joseph, MO, to demonstrate the effectiveness of GIFT to advance isobutanol production. ICM built many of the ethanol plants in the Midwest. By retrofitting ethanol plants, Gevo can lower capital and operating costs.

“We’re completely open-minded about retrofitting ethanol facilities. We may acquire ethanol plants or partner with someone who wants to make a higher value product,” says Dr. Gruber.

In February 2009, Gevo teamed up with Cargill and received exclusive rights to integrate Cargill’s microorganisms into GIFT to produce butanols from cellulosic sugars that are derived from corn stover, switchgrass, forest residues, and other sustainable feedstocks.

The Cargill platform is an industrially proven yeast technology that converts sugars into biofuels. “Cargill’s organisms and its enabling technologies give us a significant leap ahead,” continues Dr. Gruber.

Gevo also has produced renewable gasoline and jet fuel that meet or exceed specifications set by the American Society for Testing Materials, Dr. Gruber notes. The firm recently partnered with Bye Energy to distribute renewable aviation fuel to small and mid-sized airports. Small propeller planes use aviation fuel, but not commercial jets. “Only two refineries in the world make aviation fuel,” explains Dr. Gruber. Isobutanol, a 4-carbon alcohol, is readily converted into aviation fuel, an 8-carbon hydrocarbon.

Bye Energy has an extensive network of airport owners and operators who service propeller planes. About one billion gallons of aviation fuel are sold yearly. “It’s a specialty market that we can enter,” says Dr. Gruber. Gevo’s renewable aviation fuel offers business and general aviation operators an alternative to petroleum-based products that substantially reduces their carbon footprint.