(437c) Post-Combustion CO2 Capture With Ionic Liquids Involving Phase Change

Ionic liquids (ILs) are organic salts that are liquids below the boiling point of water. Non-volatility, good thermal stability and high carbon dioxide (CO₂) solubility make ILs an attractive replacement for commercially available volatile CO₂ absorbents. A new concept for CO₂ capture that uses phase change ionic liquids (PCILs) offers the potential to significantly reduce parasitic energy losses incurred from capturing CO₂ from flue gas. PCILs are solid ionic materials that react stoichiometrically and reversibly with CO₂ (one mole of CO₂ for every mole of salt at typical post-combustion flue gas conditions) and form a liquid when they react with CO₂. This allows for a novel process that uses the heat of fusion (ΔH_fus) to provide part of the heat needed to release CO₂ from the absorbent, reducing the total energy required. In addition, the phase transition yields almost a step-change absorption isotherm, which would require smaller pressure/temperature swing in the stripper. We present here detailed measurements of the CO₂ uptake, heat of absorption (ΔH_abs) and phase transition behavior for selected PCIL compounds as well as the development of an absorption isotherm model to capture the underlying thermodynamics of the CO₂ absorption and phase change process. Additionally, the performance of lab scale absorption unit and regeneration unit with a PCIL will be discussed.