August 8, 2014

UC Davis scientists search for ways to turn carbon dioxide into fuel

Carbon dioxide is a waste product of fuel burned in cars, but some UC Davis scientists are working to turn it back into fuel.

Carbon dioxide is a waste product of fuel burned in cars, but some UC Davis scientists are working to turn it back into fuel.

To accomplish the conversion, Shota Atsumi, a UC Davis chemist, is experimenting with genetically modifying bacteria.

His colleague, Louise Berben, another UC Davis chemist, makes compounds that use electricity to power chemical reactions that produce fuel.

Berben’s work focuses on making inorganic catalysts – molecules that don’t react themselves, but enable other molecules to react in new and more efficient ways – to produce useful chemicals.

One such product is formic acid, which puts the sting in ant bites but can be used as a precursor to making other chemicals used in industry – or even as a liquid fuel similar to gasoline, according to Berben.

This could be used for portable power, such as in a fuel cell in a car, but is currently far from large-scale applications. For now, small vials suffice to contain the products made in Berben’s lab.

To find a catalyst, Berben said, she takes her knowledge of chemistry and considers different ways of making molecules interact to form a product. Then her team has to figure out how to make the new catalyst, which can take months for more difficult combinations.

Some of the work must be done in glove boxes, which are filled with pure nitrogen gas – not because the catalysts are dangerous, but because they are destroyed by exposure to oxygen in the air, Berben said.

Once a new catalyst is ready, it needs an electric current to power fuel production and carbon dioxide to make formic acid.

Berben is particularly pleased by her group’s recent work using aluminum at the core of catalysts, because aluminum metal by itself is a poor catalyst.

Platinum metal is a good enough catalyst that it is used in the catalytic converters of some cars, but it’s expensive. “It would be nice to do catalysis with metals that are much more abundant,” like aluminum, she said.

William McNamara, a chemistry professor at the College of William and Mary in Virginia, agreed. He also explained that “when you have a problem this large you have a lot of collaboration.” He said scientists who work on similar chemicals are spread across numerous universities and national labs.

Growing fuel

Meanwhile, in a neighboring building, liquid the color of green grass swirls around the bottom of Erlenmeyer flasks.

The color comes from cyanobacteria, also known as blue-green algae, a common part of everyday pond scum. “They’re a lot like houseplants,” said Christine Rabinovitch-Deere, a postdoctoral scholar in Atsumi’s lab. “When they’re yellow, they’re not very happy.”

According to Rabinovitch-Deere, the swirling ensures the bacteria have an adequate supply of carbon dioxide from the air. The bacteria are photosynthetic, taking in light and turning the carbon dioxide into sugars.

The bacteria also produce chemicals such as butanediol, which can be used to make fuels, plastic or synthetic rubber, like that found in car tires.

Atsumi’s group gives the bacteria fragments of DNA, typically from other bacteria, that provide instructions for making new enzymes. Those enzymes divert some of the energy the bacteria gain from photosynthesis into what the researchers want to make.

The use of photosynthesis differs from Berben’s work, which requires electricity to power the chemical reactions.

After a few weeks, the buildup of butanediol eventually stifles the bacteria’s growth. Atsumi described the process as similar to how yeast used to produce wine or beer is eventually killed by the increasing amount of alcohol.

The low concentrations of butanediol that the bacteria make are not very toxic to humans, he said.

Atsumi explained the genetically modified cyanobacteria can’t survive outside the lab – wild bacteria would overwhelm them. “The potential risk is very low,” he said. His group kills modified bacteria no longer being used with bleach or heat before disposal.

While Atsumi said he rarely collaborates directly with people outside of his lab on this project, he said his group relies on techniques established by Susan Golden at UC San Diego. According to a review paper by Anne Ruffing at Sandia National Laboratory, several biotech companies and many researchers are investigating the potential of engineered cyanobacteria.

Scaling up

Both Berben and Atsumi indicated that more work is needed to put their research in an industrial setting.

It took Atsumi’s bacteria several weeks to produce less than a teaspoon of butanediol. The degree to which it is possible to scale up the process is unknown.

Berben said her main challenge is to make catalysts that make fuel as fast as possible and last as long as possible. Her present catalysts will last for at least few days, but her group has yet to test longer durations.

She said protecting the catalysts from harmful oxygen can be done with methods already used in industrial chemical production.

While some companies, such as France-based Pragma Industries, have been working with formic acid fuel technology, these fuel cells have yet to be implemented on a large scale.

Atsumi said one limit for his bacteria is how well they can use light to not only grow, but make chemicals. Other groups, such as that of David Britt at UC Davis, are studying ways to make photosynthesis more efficient.

Another issue on the industrial scale is getting enough light to the bacteria, said John Oliver, a postdoctoral scholar working with Atsumi. If the bacteria are grown in a large vat, all the light will be taken up by bacteria near the surface, leaving the ones underneath in the dark.

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