Sunshine to petrol

By Chris Burroughs

Researchers are building a device intended to chemically reenergize carbon dioxide using concentrated solar power. The resulting carbon monoxide could be used to make hydrogen or serve as a building block of combustible liquid fuels.

The prototype device, called the Counter Rotating Ring Receiver Reactor Recuperator (CR5, for short), will break carbon-oxygen bonds in carbon dioxide to form carbon monoxide and oxygen in two distinct steps.

Liquid solar fuel is the end product – methanol, gasoline, or other combustible liquid made from water and the carbon monoxide. The Sandia research team calls the approach “Sunshine to Petrol” (S2P).

CR5 inventor Rich Diver says the original purpose of the device was to break down water into hydrogen and oxygen to fuel a future hydrogen economy. They soon realized that the CR5 also could break down carbon dioxide to distill carbon monoxide – a needed component of liquid fuel. They have shown proof of concept and now are completing a prototype device.

Team member Ellen Stechel says scientists have known for a long time that recycling carbon dioxide is possible, but many doubted it could be done economically.

“This invention, though probably a good 15 to 20 years away from being on the market, holds a real promise of being able to reduce carbon dioxide emissions while preserving options to keep using fuels we know and love,” she says. “Recycling carbon dioxide into fuels is an attractive alternative to burying it.”

Sandia’s LDRD program supports the effort, which has attracted interest and some funding from the Defense Department’s Defense Advanced Research Projects Agency (DARPA).

“What’s exciting about this invention is that it will result in fossil fuels being used at least twice, meaning less carbon dioxide being put into the atmosphere and a reduction of the rate that fossil fuels are pulled out of the ground,” Diver says.

As an example, he says, coal would be burned at a clean coal power plant. The carbon dioxide from the burning of the coal would be captured and reduced to carbon monoxide in a CR5. The carbon monoxide would then be the starting point of making gasoline, diesel, jet fuel, or methanol.

After the synthesized fuel is made from carbon monoxide, it could be transported through a pipeline or put in a truck and hauled to a gas station, just like gasoline refined from petroleum is now. Plus, says Diver, it would work in ordinary gasoline and diesel engine vehicles.

Team member Jim Miller says that while the first step would be to capture the carbon dioxide from concentrated pollution sources, the ultimate goal would be to snatch it out of the air. An S2P approach that includes atmospheric carbon dioxide capture might ultimately produce carbon-neutral liquid fuels.

“Our overall objective with this prototype is to demonstrate the practicality of the CR5 concept and to determine how test results from small-scale testing can be expanded to work in real devices,” Miller says. “The design is conservative compared to what might eventually be developed.”

Diver says the CR5 prototype, located at Sandia’s National Solar Thermal Test Facility in Albuquerque, should be completed soon. Initial tests will break down water into hydrogen and oxygen. That will be followed by tests that similarly break down carbon dioxide into carbon monoxide and oxygen.

“The method of synthesis we’re studying — known as radiolysis — breaks down the water structure allowing it to react with metal salts to form nanoparticles, a synthetic approach that is flexible and versatile for making large quantities of nanoparticle compositions that can’t be easily created otherwise,” she says.

The research team has proven that the chemistry works repeatedly through multiple cycles without performance loss and on practicable cycle times.

“We just have to do it all in one continuous working device,” says team member Nathan Siegel.