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 N₂ (50:50% molar ratio). We examine the nature of the interaction of CO₂ and N₂ with reline employing quantum chemical methods. We focus on explaining the mechanism by which CO₂ and N₂ bind to reline and the reason for the high selectivity for absorption of CO₂ compared to N₂. We analyze the dynamics, energetics, and binding motifs for CO₂ and N₂ 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 N₂ is due to the interplay between attractive electrostatic and charge polarization forces with opposing entropic effects, which shift the energetic balance and make the N₂ absorption unfavorable in reline.