03 January 2008

Cellulosic Butanol: The Smart Biofuel

It is becoming obvious that corn (maize) ethanol is not a good approach to biofuels. Besides driving up the world price of maize--making many foods less affordable to consumers--and taking up food croplands for growing fuel, the energy yield from maize ethanol simply does not make sense. Fortunately for biofuels, spending on biofuel research has risen to unprecedented levels.

Even better, much of the spending is for projects that actually make sense on many levels. One sensible approach to biofuels, is using genetic engineering to modify micro-organisms to produce butanol from biomass cellulose/lignin.
Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have developed a new method for producing next-generation biofuels by genetically modifying Escherichia coli bacteria to be an efficient biofuel synthesizer. The method could lead to mass production of these biofuels.

The strategy, developed by UCLA professor of chemical and biomolecular engineering James Liao, postdoctoral fellow Shota Atsumi and visiting professor Taizo Hanai, appears in the Jan. 3 issue of the journal Nature....Higher-chain alcohols have energy densities close to gasoline, are not as volatile or corrosive as ethanol, and do not readily absorb water. Furthermore, branched-chain alcohols, such as isobutanol, have higher-octane numbers, resulting in less knocking in engines. Isobutanol or C5 alcohols have never been produced from a renewable source with yields high enough to make them viable as a gasoline substitute.

"These alcohols are typically trace byproducts in fermentation," Liao said. "To modify an organism to produce these compounds usually results in toxicity in the cell. We bypassed this difficulty by leveraging the native metabolic networks in E. coli but altered its intracellular chemistry using genetic engineering to produce these alcohols."

The research team modified key pathways in E. coli to produce several higher-chain alcohols from glucose, a renewable carbon source, including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol.

This strategy leverages the E. coli host's highly active amino acid biosynthetic pathway by shifting part of it to alcohol production. In particular, the research team achieved high-yield, high-specificity production of isobutanol from glucose.

UCLA has granted a license for this technology to Gevo.

Achieving a high yield of iso-butanol from glucose is the second step in renewable biofuel that burns in modern gasoline engines--without the need for expensive flex-fuel technology. The first step is achieving high yields of glucose from biomass--cellulose/lignin. Genetic engineering can help with that as well, using designed organisms in mass bioreactors to convert pre-processed biomass residue into glucose to feed into the Step 2 mass bioreactors producing isobutanol.

High yields from both steps in the process are important for cellulosic butanol to become an economic alternative to gasoline. Gevo is a favourite of Richard Branson's Virgin Companies, and Vinod Khosla's Khosla Ventures.

Bio-butanol and Bio-diesel both have excellent long-term potential for replacing fossil fuels in conventional internal combustion engines. Ethanol is for drinking, and should stay that way.

Update 8 Jan 08: For a look at some more ambitious biotech approaches to creating biosynthetic fuels, see here. The truth is, biological systems can make virtually any organic molecules. Which is what I have been saying for a long time. Peak oil, meet biology.

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