DIRTY COAL: Dissolving CO2 with ionic liquids is one promising new strategy for cleaning up coal plants.
ISTOCKPHOTO/BRONSWERK

As Congress debates ways to encourage coal-fired power plants to capture carbon dioxide emissions and store it underground, scientists are racing to find cleaner and more efficient ways of collecting the greenhouse gas.

Currently, the few coal plants that are capturing CO2 on a commercial scale use technology that employs monoethanolamine, a general-purpose solvent that has been around for 75 years that is nonselective, corrosive, requires large equipment and is not effective under all conditions.

So scientists have been laboring for years to find cleaner, more efficient ways of separating CO2 from flue gas.

One method that has been under development for the past decade uses ionic liquids to dissolve CO2, eliminating it from a coal plant's gas stream.

"With ionic liquids serving as the solvent, the process could be a lot cleaner and more accessible than what is used today," said Amitesh Maiti, a physicist at Lawrence Livermore National Laboratory.

Ionic liquids are a special type of molten salt that melts at low temperatures and has significant advantages in carbon capture over traditional techniques. For one, they do not evaporate, even in high temperatures. And they have high chemical stability, low corrosion rates, extremely small vapor pressure and a large number of ion choices that could be used to dissolve CO2.

But even ionic liquids have limitations, Maiti said. "There are an infinite number of combinations for ionic liquids," he said.

In a paper published in the current issue of ChemSusChem, Maiti writes that ionic liquids have been experimentally demonstrated to be efficient solvents for CO2, providing data that can be used to optimize the use of ionic liquids for CO2 capture.

But "each new experiment costs time and money and is often hindered because a specific [ionic liquid] may not be readily available," he wrote.

So Maiti has developed a strategy that can reliably screen any solvent -- including ionic liquids -- for high CO2 capture efficiency.

"What I have is a computational strategy, which is based on models that have been developed," he said in an interview. "I applied the model to calculating the solubility of CO2 in any ionic liquid or any solvent, for that matter."

He added, "It's a great advantage to have a method that can quickly and accurately compute CO2 solubility in any solvent, especially under the range of pressures and temperatures as would be found in a coal-fired power plant."

Maiti has used his computational method to predict new solvent classes that would be able to dissolve nearly two times more CO2 than the most efficient solvents that have been experimentally demonstrated.

"I'm not claiming to have the highest solubility," Maiti said. "My idea is just to show the scientific community to use this strategy to determine high solubility for CO2. We have barely scratched the surface of possibilities."

The model could be used to discover practical solvents with significantly higher CO2 capture efficiency, he said.

Reprinted from Greenwire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500