Quantum Chemical Simulations of CO₂ and N₂ Capture in Reline, a Prototypical Deep Eutectic Solvent

Deep eutectic solvents such as reline are an emerging class of low-cost, environmentally friendly solvents with tunable properties that are potentially applicable for the capture and separation of CO2. Experimental measurements showed that a reline-based membrane contactor can capture and separate CO2 via physisorption through a dissolution process with 96.7% purity from a mixed gas containing CO2 and N-2 (50:50% molar ratio). We examine the nature of the interaction of CO2 and N-2 with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO2 and N-2 bind to reline and the reason for the high selectivity for absorption of CO2 compared to N-2. We analyze the dynamics, energetics, and binding motifs for CO2 and N-2 in reline employing density functional theory, density functional tight binding, and ab initio molecular dynamics. We also investigate the effect of reline on the vibrational spectra of CO2 and reline. Our simulations indicate that the selective capture of CO2 from the mixture of CO2 and N-2 is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N-2 absorption unfavorable in reline.