UCLA researchers use electricity to produce advanced biofuels
Led by James Liao, UCLA’s Ralph M. Parsons Foundation Chair in chemical engineering, researchers at UCLA’s Henry Samueli School of Engineering and Applied Science have demonstrated a novel method for converting carbon dioxide within an intermediary, such as formic acid, into higher alcohols like isobutanol and 3-methyl-1-butanol using renewable electricity. The team’s work was published March 30 in the journal Science.
Liao explained to Biorefining Magazine that he and his team found a way to genetically engineer a lithoautotrophic microorganism, called Ralstonia eutropha, to produce higher biobased alcohols in an electrobioreactor using carbon dioxide as the sole carbon source and electricity as the sole energy input. The electricity required for this process can be generated from solar panels, wind or other renewable sources.
Liao elucidated that since photosynthesis is nature’s way of converting light energy into chemical energy and storing it in sugar units, he and his team were able separate the light reactions and dark reactions; the light reaction converting light energy to chemical energy and the dark reaction converting carbon dioxide to sugar, which doesn’t directly need light to occur.
“Typically, the photosynthetic organism takes light and converts light through an intermediate that bacteria can use to drive CO2 fixation,” Liao said. “Now, we’ve split these two parts. We form light through an intermediate that we use through man-made devices. The second part, from intermediate to the fuel, occurs via a biological system. The organism has to harvest light and convert light through the intermediate that the cell can use and then fix CO2 in order to convert the intermediate into the specified fuel.”
While the Ralstonia organism has an intrinsic ability to fix carbon dioxide, it does not however, have the capability to produce any usable fuel, according to Liao.
“What we did was genetically introduce a set of enzymes so that it can convert metabolic intermediates in the cell to the fuel that we’re interested in,” Liao said. “In nature, the Ralstonia organism can fix carbon dioxide without light; in fact, it doesn’t do photosynthesis at all. That’s why it’s lithoautotrophic. It takes in the formic acid and fixes carbon dioxide to produce the selected compounds like isobutanol.”
Liao said hydrogen would traditionally be used as the intermediary rather than formic acid for driving carbon dioxide fixation in lithoautotrophic microorgansims like Ralstonia, but he said hydrogen’s low solubility in water, low mass-transfer rate and safety issues limited the efficiency and scalability of the process. Instead, the team found formic acid to be a favorable substitute as the energy carrier.
“[Formate] is much more soluble in water, nontoxic and not as explosive hydrogen,” Liao said.
The combination of the electrochemical formic acid production and the biological carbon dioxide fixation and higher alcohol synthesis allows for the potential of electricity-driven bioconversion of carbon dioxide to a variety of end products in addition to isobutanol and 3-methyl-1-butanol, according to Liao, adding that the process is capable of also yielding other organic compounds pertinent to the biorefining industry such as n-butanol, ethanol and methyl esters.
The work at UCLA is currently one of 13 projects supported by a U.S. DOE Advanced Research Projects Agency-Energy (ARPA-E) grant that are working to use microorganisms to create liquid biofuels under the Electrofuels program, originally awarded to UCLA in July 2010. Liao is also heading a separate project in parallel with the Electrofuels program, also funded by the ARPA-E, within the Plants Engineered to Replace Oil (PETRO) program, which entails redesigning CO2 fixation pathways in plants.
For more information about the ARPA-E’s Electrofuel and PETRO projects, click here.