Exploring the potential of ethylenediamine based protic ionic liquids for carbon capture: A study on thermophysical properties and CO2 absorption behavior

The objective of the study is to synthesize economical and facile ethylenediamine (ED) based protic ionic liquids (PILs) containing various carboxylate anions for CO₂ capture for post-combustion method. The PILs were synthesized using a straightforward process, and the behavior of their CO₂ absorption was investigated in relation to the alkyl chain of odd and even chain anions. The PILs were characterized using ¹H NMR, ¹³C NMR, and HRMS techniques. The study results indicate that ED-ILs with longer alkyl chains are better at absorbing CO₂. Among all the PILs, [ED][Hep] exhibited the highest absorption capacity except [ED][But], absorbing 0.26 CO₂/mol of IL at 298K and 0.1 MPa. The thermophysical properties, including density, sound speed, viscosity, and refractive index of neat ED-based PILs, were tested at different temperatures and 0.1 MPa. Furthermore, the derived parameters such as expansion coefficient (α), molecular volume (V), isentropic compressibility (βs), lattice potential energy (U_POT), standard entropy (S⁰), Intermolecular free length (L_f) and free volume (Vm) were determined using experimental parameters. It was shown that these characteristics were directly related to the PILs ability to absorb CO₂. Overall, the investigation demonstrated that [ED][But] offers a great potential for utilization as a CO₂ absorption solvent because of its high absorption capacity and special qualities as a PIL.