Dr. Amr Henni

Abstract:

The primary goal of this study is to investigate the potential of particular ionic liquids (ILs) in capturing CO₂ for the sweetening of natural and other gases. The solubility of CO₂ was measured in three distinct ILs, which shared a common anion (Triflate, TfO) but differed in their cations. The selected ionic liquids were {1-Butyl-3-methylimidazolium triflate [BMIM][TfO], 1-Butyl-1-methylpyrrolidinium triflate [BMP][TfO], and 1-Butyl-4-methyl-pyridium triflate [MBPY][TfO]}. The solvents were screened based on results from a molecular computational study that predicted low CO₂ Henry's Law constants. Solubility measurements were conducted at 303.15 K, 323.15 K, and 343.15 K, and pressures up to 1.5 MPa, using a gravimetric microbalance. CO₂ experimental results were modeled using the Peng-Robinson equation of state with three mixing rules. For the three ILs, the Non Random Two Liquid - WS mixing rule regressed the data with the lowest average deviation percentage of 1.24%. The three solvents had similar alkyl chains but slightly different polarities. [MBPY][TfO], with the largest size, exhibited the highest CO₂ solubility at all three temperatures. Calculation of its relative polarity descriptor (N) shows it was the least polar of the three ILs. Conversely, [BMP][TfO] showed the highest Henry's Law constant (lowest solubility) across the studied temperature range. Comparing the results to published data, the study concludes that triflate-based ionic liquids with three fluorine atoms have a lower capacity for CO₂ compared to bis(trifluoromethylsulfonyl)imide (Tf₂N)-based ionic liquids with six fluorine atoms. Additionally, the study provided data on the enthalpy and entropy of absorption. A final comparison shows that the ILs had a lower CO₂ capacity than Selexol, a solvent widely used in commercial carbon capture operations. Compared to other ILs, the results confirm that the type of anion had a more significant impact on solubility than the cation.