Salting Away Greenhouse Gas

Author: John Monczunski

About 40 percent of all the carbon dioxide pollution produced in the United States today comes from the coal-fired power plants that make half the nation’s electricity. Currently, power companies aren’t required to remove CO2 from their smokestacks. If they were, conventional technology would add about 30 percent to your electric bill.

Clearly, a cheaper solution to the greenhouse gas problem is needed, and some Notre Dame chemical engineers believe salts may be the answer. Not the kind you sprinkle on french fries, but “molten salts,” also known as ionic liquids. These manmade chemical salts are fluid at room temperature.

Ed Maginn, Joan Brennecke and William Schneider, Notre Dame chemical and biomolecular engineering professors, first recognized their potential a few years ago while studying the compounds for possible use as nontoxic, “green” industrial solvents. In the course of that work, the Notre Dame researchers found that nitrogen, a large component of power plant emissions, is insoluble in an ionic liquid. “And that was when we first got the idea they might be a useful tool for doing gas separations,” Brennecke says.

Subsequent work revealed that ionic liquids do indeed have the ability to soak up a good deal of CO2. The basic idea in most carbon dioxide reduction schemes is to separate CO2 from the flue gas and then sequester it by pumping it down and out of the atmosphere into deep saline aquifers in old, played-out oil well fields.

Ionic liquids have the potential to be more economical than such reduction methods because they work at higher temperatures and are less corrosive to plumbing. With the conventional water-based technology, power plant gases must first be cooled before they are passed through the capturing chemicals. This method also reacts with sulfur dioxide, corroding pipes.

Currently, the Notre Dame research team is working to fine-tune the amount of energy needed to release the CO2. from the ionic liquid and to optimize its capacity to carry the gas. DTE, the Detroit power company; Babcock & Wilcox, a power plant construction firm; and Air Products, a gas separation firm, are partners in the research.