Let’s use salt to capture CO2: Ionic liquid carbon capture

Researcher: Joan Brennecke, University of Notre Dame

Who knew salt could be used to capture CO2? But this isn’t your ordinary table salt. Scientists at the University of Notre Dame are working on liquid salt technology to help clean up coal-fired power plants.

Joan Brennecke, director of Notre Dame’s Energy Center, leads an ARPA-E funded project based on a newly discovered class of ionic liquid, or liquid salt. Unlike other ionic liquids that are liquid at room temperature, this class of ionic liquid is solid at room temperature, but melts when reacted with CO2. This characteristic is key for an energy-efficient carbon capture process.

Boasting a high capacity to uptake CO2, the ionic liquid selectively reacts with CO2 in flue gas, the waste gas produced from fuel combustion, becoming liquid as it does so. The clean flue gas is then pumped out, separating it from the CO2 ionic liquid compound.

Heat is applied to remove the CO2 from the ionic liquid for sequestration. Once CO2 separates from the ionic liquid, the ionic liquid re-solidifies and generates heat. This heat is cycled back to the CO2 removal step, which reduces the energy required for the process.

The captured CO2 can then be sequestered or used for another application. The ability to recapture and reuse the waste heat is a key to the technology’s viability, since most carbon capture technologies demand about 30 percent of a plant’s generating capacity, according to Brennecke. Carbon capture effectively downgrades a 100 MG power plant to a 70 MG facility.

“That’s a huge penalty. The goal of everybody who’s trying to come up with better ways of removing CO2 from flue gas … is to try to do it with less energy,” Brennecke said.

The carbon capture process being developed by Notre Dame may reduce that penalty to 20 percent. There is a thermodynamic minimum of about 10 percent.

The investment required poses another challenge to adoption of carbon capture, both legislatively and practically. At the current state of development, this technology would require that an entire chemical plant be built adjacent to the power plant.

Legislators won’t pass regulations that impose such a financial and developmental burden on power plants. Without regulations, power plants don’t feel compelled to capture the carbon they produce.

“The goal here would be ‘can we come up with technology that would be less expensive and use less energy’” in order to be adopted with ease, Brennecke said.

The project grew out of Brennecke’s work with supercritical CO2, which is CO2 at high pressure and temperature that has properties of both a liquid and gas. While attending a conference, Brennecke and a colleague came up with the idea of pairing supercritical CO2 and ionic liquid as an extraction technique unrelated to carbon capture. They noticed that a lot of the CO2 was being dissolved in the ionic liquid, which is how they segued the research into carbon capture technology.

The project, now in the demonstration phase, began ARPA-E in 2010. It has an ARPA-E award of $2.56 million running through mid-2013. To complement the ARPA-E funding, the Notre Dame researchers have a new project started fall 2012 funded by the Global Climate and Energy Project (GCEP), which is led by Stanford University, to further develop materials for CO2 capture.


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