Carbon Dioxide Selectivity over Ethane in Promising Bis Tri (Fluoromethylsulfonyl) Imide-Based Ionic Liquids

This research addresses the critical challenge of CO₂ capture by exploring innovative ways to avoid ethane (C₂H₆) co-absorption in natural gas sweetening operations. The solubility of Ethane (C₂H₆) was measured in three ionic liquids (ILs) with similar anions, 1-decyl-3-methyl imidazolium bis (trifluoro methylsulfonyl imide) [IL-1], 1-hexadecyl-3-methylimidazolium bis (trifluoro methylsulfonyl imide) [IL-2], and triethytetra-decyl ammonium bis (trifluoromethylsulfonyl imide) [IL-3]. The solubility experiments were investigated at 303.15 K and 343.15 K with pressures reaching 1.2 MPa. Among the ILs, [IL-2] exhibited the highest ethane absorption capacity due to its extended alkyl chain. The Peng-Robinson equation of state (PR-EoS) and three (3) distinct mixing rules provided robust correlations for the solubility data. Results demonstrate the inferior performance of [IL-1], [IL-2], and [IL-3] compared to Selexol/Genosorb 1753. The selectivity of Ethane (C₂H₆) over CO₂ was determined, with the overall selectivity ranking as follows: [IL-1] > [IL-3] > [IL-2]. A comparison of these selectivity values with published IL data indicated that these three ILs are most effective when used in applications targeting CO₂ capture in the absence of Ethane (C₂H₆), such as in the case of flue gas. They will most probably be used with an amine blend. Additionally, the Enthalpy and entropy of absorption provided valuable insights, demonstrating Ethane's weaker interactions and lower solubility than CO₂. These findings emphasize the critical role of IL structure in determining ethane solubility and highlight the potential of customized ILs for optimizing gas-separation processes.