Scientists Clearly See an Emissions-free Highway

Researchers at the Georgia Institute of Technology in Atlanta have developed a strategy to capture, store, and eventually recycle carbon from vehicles to prevent the pollutant from finding its way from a car tailpipe into the atmosphere. They envision a zero-emission car and a transportation system completely free of fossil fuels.

Technologies to capture carbon dioxide (CO2) emissions from large-scale sources such as power plants have recently gained some impressive scientific ground, but nearly two-thirds of global carbon emissions are created by much smaller polluters — automobiles, transportation vehicles, and distributed industrial power generation applications.

The team's goal is to create a sustainable transportation system that uses a liquid fuel and traps the carbon emission in the vehicle for later processing at a fueling station. The carbon would then be shuttled back to a processing plant where it could be transformed into liquid fuel. Currently, researchers are developing a fuel processing device to separate the carbon and store it in the vehicle in liquid form.

The research, published in Energy Conversion and Management, was funded by NASA, the U.S. Department of Defense NDSEG Fellowship Program and Georgia Tech's CEO (Creating Energy Options) Program.

"Presently, we have an unsustainable carbon-based economy with several severe limitations, including a limited supply of fossil fuels, high cost and carbon dioxide pollution," said Andrei Fedorov, associate professor in the Woodruff School of Mechanical Engineering at Georgia Tech and a lead researcher on the project. "We wanted to create a practical and sustainable energy strategy for automobiles that could solve each of those limitations, eventually using renewable energy sources and in an environmentally conscious way."

The school's near-future strategy involves capturing carbon emissions from conventional (fossil) liquid hydrocarbon-fueled vehicles with an onboard fuel processor designed to separate the hydrogen in the fuel from the carbon. Hydrogen is then used to power the vehicle, while the carbon is stored on board the vehicle in a liquid form until it is disposed at a refueling station. It is then transported to a centralized site to be sequestered in a permanent location currently under investigation by scientists, such as geological formations, under the oceans, or in solid carbonate form.

Georgia Tech settled on a hydrogen-fueled vehicle for its carbon capture plan because pure hydrogen produces no carbon emissions when it is used as a fuel to power the vehicle. The fuel processor produces the hydrogen on-board the vehicle from the hydrocarbon fuel without introducing air into the process, resulting in an enriched carbon byproduct that can be captured with minimal energetic penalty. Traditional combustion systems, including gasoline-powered automobiles, have a combustion process that combines fuel and air — leaving the carbon dioxide emissions highly diluted and very difficult to capture.

"We had to look for a system that never dilutes fuel with air because once the CO2 is diluted, it is not practical to capture it on vehicles or other small systems," said David Damm, PhD., candidate in the School of Mechanical Engineering, the lead author on the paper and Fedorov's collaborator on the project.

The hydrogen economy presents a possible solution to carbon emissions and another roadblock — infrastructure. While liquid-based hydrogen carriers could be conveniently transported and stored using existing fuel infrastructure, the distribution of gaseous hydrogen would require the creation of a new and costly infrastructure of pipelines, tanks and filling stations.

The team created a fuel processor, called CO2/H2 Active Membrane Piston (CHAMP) reactor, which is capable of efficiently producing hydrogen and separating and liquefying CO2 from a liquid hydrocarbon or synthetic fuel used by an internal combustion engine or fuel cell. After the carbon dioxide is separated from the hydrogen, it can then be stored in liquefied state on-board the vehicle. The liquid state provides a much more stable and dense form of carbon, which is easy to store and transport.

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