Innovative process removes carbon from air anywhere

Until now, carbon capture has focused largely on removing greenhouse gases at their source, such as the emissions of power plants, refineries, concrete plants and other industries.

But University of Cincinnati Professor Joo-Youp Lee said the Golden Fleece of carbon capture is drawing carbon dioxide directly from the atmosphere, which is much, much harder.

“The concentrations of carbon dioxide in the atmosphere are so low,” he said. “It would be like trying to remove a handful of red ping-pong balls from a football stadium full of white ones.”

He is a professor of chemical engineering in UC’s College of Engineering and Applied Science.

But Lee and his students have developed a promising system of removing carbon dioxide at about 420 parts per million from the air. And with his process called direct air capture, it can be deployed virtually anywhere.

Power plants and transportation are responsible for about 53% of all carbon dioxide emissions. The remaining emissions are generated by industry, commercial and residential buildings, agriculture and other human activities.

The system Lee developed in his lab uses electricity to separate carbon dioxide.  But he is advancing his system by using hot water instead of electricity or steam, making it more energy efficient than other carbon-capture systems. And it’s robust enough to last for thousands of cycles.

To test his system, Lee built a benchtop model about the length of a pool noodle. Air from outside the building is pumped through a canister. Lee said they can’t use indoor air because it typically contains more carbon dioxide from the people using the building.

Inside the canister, the air whooshes through a honeycomb-like block wrapped with carbon fiber that Lee’s lab had custom manufactured. The individual cells of the block are coated with a special adsorbent material that Lee’s team designed to capture carbon dioxide. Gauges on the air intake and exit measure the amount of carbon dioxide in the air. When the readings on the outlet of the block begin to climb, Lee’s students know it’s time to heat the structure to remove the trapped carbon dioxide with a vacuum pump and begin the process again.

UC researchers have been able to repeat the process more than 2,000 times without seeing any drop-off in efficiency or degradation of the materials. But Lee said he thinks 10,000 cycles is within reach. This efficiency would make the system more economically appealing.

Lee’s team scaled up the project in one of UC’s high-bay engineering labs, where students work on engines and other big industrial projects. Here, Lee maintains a climate-controlled environmental chamber where he can do larger-scale experiments of his concept.

They built a person-sized canister that again draws air from outside the building. But in this sealed room they can control temperature, humidity and wind speed. And they use larger honeycombed blocks the size of a loaf of bread.

“I think it’s a great project. We’re doing some real applications that can help the environment,” UC postdoctoral fellow Soumitra Payra said.

With the promise of his demonstration system, Lee is hoping the U.S. Department of Energy will continue to support his plans to develop an industrial-size prototype.

“Our technology has proven to reduce the heat required for the desorption by 50%. That’s a really big improvement,” he said. “By using half of the energy, we can separate out carbon dioxide more efficiently. And we can make the cycle longer and longer.”

Lee said these systems could be instrumental in addressing climate change as demand for electricity is expected to surge in years to come.

Lee’s research is supported through the U.S. Department of Energy National Energy Technology Laboratory.