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Presidential Green Chemistry Challenge: 2010 Academic Award - James C. Liao and Easel Biotechnologies, LLC

James C. Liao, Ph.D., of the University of California, Los Angeles

Easel Biotechnologies, LLC


Recycling Carbon Dioxide to Biosynthesize Higher Alcohols

Innovation and Benefits: Ethanol made by fermentation can be used as a fuel additive, but its use is limited by its low energy content. "Higher" alcohols (those with more than two carbons in the molecule) have higher energy content, but naturally occurring microorganisms do not produce them. Dr. James Liao has genetically engineered microorganisms to make higher alcohols from glucose or directly from carbon dioxide. His work makes renewable higher alcohols available for use as chemical building blocks or as fuel.

Summary of Technology: Higher alcohols, especially those with 3–8 carbon atoms, are useful as chemical feedstocks and transportation fuels. The efficient biosynthesis of these alcohols directly from carbon dioxide (CO2) or indirectly from carbohydrates would reduce net carbon emissions. Unfortunately, native organisms do not synthesize these alcohols. Until now, none of these alcohols have been synthesized directly from CO2, and alcohols above five carbons have never been synthesized in the biosphere.

Dr. Liao, an Easel Biotechnologies board member and professor at the University of California, Los Angeles (UCLA), has developed a microbial technology to produce alcohols with 3–8 carbon atoms from CO2. His technology leverages the highly active amino acid biosynthetic pathway, diverting its 2-keto acid intermediates toward alcohols. With this technology, Professor Liao and his group have produced isobutanol from glucose in near-theoretical yields with high efficiency and specificity. They also transferred the pathway into a photosynthetic microorganism, Synechococcus elongatus PCC7942, which produces isobutyraldehyde and isobutanol directly from CO2. The engineered strain produces isobutanol at a higher rate than those reported for ethanol, hydrogen, or lipid production by cyanobacteria or algae. This productivity is also higher than the current rate of ethanol production from corn. The technology shows promise for direct bioconversion of solar energy and CO2 into chemical feedstocks.

Higher alcohols are also good fuels. As fuel substitutes, they have several advantages over ethanol, including higher energy density, lower hygroscopicity, and lower vapor pressure leading to better air quality. After excretion by the cells as aldehydes, the products are readily stripped from the bioreactor, avoiding toxicity to the microbes. Chemical catalysis then converts the harvested aldehydes to alcohols or other chemicals.

If 60 billion gallons of higher alcohols were used each year as chemical feedstocks and fuel (replacing 25 percent of gasoline), Dr. Liao's technology could eliminate about 500 million tons of CO2 emissions or about 8.3 percent of the total U.S. CO2 emissions. Easel Biotechnologies is commercializing the CO2-to-fuels technology under exclusive license from UCLA.

Podcast on the technology:

(MP3, 320 KB, 1:04 minutes)

Read the text of this podcast.

Other resources:

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