CO2 Solubility in Aqueous Solutions of Amine–Ionic Liquid Blends: Experimental Data for Mixtures with AMP and MAPA and Modeling with the Modified Kent–Eisenberg Model

Carbon dioxide (CO₂) capture using alkanolamines remains the most mature technology, yet faces challenges including solvent loss, high regeneration energy and equipment corrosion. Ionic liquids (ILs) are proposed as alternatives, but their high viscosity and production costs hinder industrial use. Thus, blending ILs with amines offers a promising approach. This work presents new experimental data for aqueous blends of 1-butyl-3-methylimidazolium hydrogen sulfate, Bmim+HSO4-, with 2-amino-2-methyl-1-propanol (AMP) and 3-(methylamino)propylamine (MAPA) and for choline glycine, Ch+Gly-, with AMP, modeled using the modified Kent-Eisenberg approach. It was shown that substituting a portion of the amine with Bmim+HSO4- reduces CO₂ uptake per mole of amine due to the lower solution's basicity, despite the added sites for physical absorption. In contrast, the replacement of an amine portion with Ch+Gly- enhances both physical and chemical interactions, leading to increased CO₂ solubility per mole of amine. Finally, replacing a small portion of water with [Ch+][Gly-] does not significantly alter the bulk CO₂ solubility (moles of CO₂ per kg of solvent) but lowers the solvent's vapor pressure. Given the non-toxic nature of [Ch+][Gly-], the resulting solvent poses no added environmental risk. Model predictions agree well with experimental data (deviations of 2.0-11.6%) and indicate low unreacted amine content at CO₂ partial pressures of 1-10 kPa for carbamate-forming amines, i.e., Gly-, and MAPA. Consequently, at higher CO₂ partial pressures, the solubility increases due to carbamate hydrolysis and molecular CO₂ dissolution.