Carbon Capture Facilitated By Ionic Liquid’s Phase Change

An ionic-liquid-based material that changes from solid to liquid upon reacting with carbon dioxide could lower the energy costs of capturing CO₂ from power plant emissions, reported Joan F. Brennecke of the University of Notre Dame. The so-called phase-change ionic liquid (PCIL) is composed of a tetraethylphosphonium salt that is solid at normal postcombustion flue gas temperatures of 40 to 80 °C. CO₂ reacts stoichiometrically and reversibly with an aprotic heterocyclic anion, reducing the melting point of the material and turning the solid into a liquid (Energy Fuels 2014, DOI: 10.1021/ef501374x). In the proposed process, a slurry of the solid PCIL and PCIL-CO₂ would be used in an absorber to capture more CO₂. The resulting liquid would be heated to drive off the CO₂ for storage elsewhere while the PCIL is reused. The combined enthalpies of the CO₂ binding and release reactions and the associated phase changes would reduce the external energy consumed by carbon capture to about 23% of the energy produced by a conventional coal power plant, compared with 28% for current carbon capture systems.