CO2 Capture Using 1-Hexyl-3-Methylimidazolium Based Ionic Liquids

Current post combustion CO₂ capture systems in power plants typically employ amine based solvent, such as monoethanolamine (MEA), to capture CO₂ from flue gas followed by a desorption (or solvent regeneration) step, usually a stripping column, to recover the captured CO₂ and regenerate the solvent. The MEA solvent has high heat of reaction with CO₂ that leads to higher stripping energy consumption during CO₂ recovery, thus making amine scrubbing an energy expensive process. The solvents suggested for CO₂ capture in this work belong to a group of compounds called ionic liquids (ILs). Many ILs have shown a remarkably good CO₂ solubility. Ionic liquids have also shown good selective CO₂ absorption, thus making ILs a potential candidate for CO₂ capture from flue gas. Since CO₂ absorption in ILs involves physisorption (physical absorption) rather than chemisorption (chemical absorption) of CO₂ in amine based solvents, there is a potential to develop energy efficient ionic liquid based absorption-stripping process. The choice of the ionic liquid, 1-hexyl-3-methylimidazolelium tetrafluoroborate (HMIM)BF₄, has not been optimized but was chosen based on chemical absorption behaviour and the desire to understand performance. Engineering design estimates indicate that the investment for the ionic liquid process will be 11% lower than the amine based process and provide a 12% reduction in equipment footprint.