Effects of various anions and cations in ionic liquids on CO₂ capture

Blends of ionic liquids (ILs) with monoethanolamine (MEA) in 1-hexanol were employed to enhance CO₂ removal in comparison with that of pure MEA. A series of hydrophobic and hydrophilic 1-alkyl-3-methylimidazolium-based ionic liquids ([C_n-mim][Ac], [C_n-mim][Cl], and [C_n-mim][Tf₂N] with n = 2 or 4) were studied to investigate the absorption/desorption performance, which is known to be affected by changes in the type of anion used and the alkyl chain length in the cation. Three different weight percentages of ILs were added to 20 wt% MEA, and the maximum amine concentration in the liquid was obtained as 30 wt/wt%. The absorption capacity (or equilibrium solubility) was noted to be highly dependent on the selection of the anion, whereas the choice of cation had a minor effect. The results revealed that the addition of IL significantly improved the CO₂ capture performance, and indicated a favorable loading ratio. The [bmim][Ac] IL was found to result in the highest CO₂ equilibrium loading (0.89 mol CO₂/(mol [bmim][Ac])) compared to that in other blends. Moreover, the interactions between CO₂ and the blend systems were characterized using Fourier transform infrared spectrometry (FTIR) to analyze the reusability and potential performance losses of the solvent systems.