Solubility of Gases in Choline Chloride-Based Deep Eutectic Solvents from Molecular Dynamics Simulation

Choline chloride-based deep eutectic solvents (DESs) are a new class of green solvents that are liquid in the range of operating conditions for most of the process industries. Due to their environmentally friendly nature, cost-effectiveness, easy preparation, and recyclability, they are popular and possible alternatives for conventional solvents in the process industries. In the present work, molecular dynamics (MD) simulations were employed to understand the free energy of solvation of four different gas molecules (H2S, CO2, CH4, and N2) in DESs (ethaline, reline, glyceline, and oxaline); thereafter, the Henry's law constant, solvation enthalpy, entropy, and selectivity were computed.The trends observed for solubility revealed that all of the studied DESs followed the order of H2S > CO2> CH4> N2, consistent with similar observations in other solvents. Similarly, the solvation enthalpy (ΔHsol) for the investigated gases in the DESs followed a similar order of H2S > CO2> CH4> N2. Ideal gas selectivities (SCO2/CH4 and SH2S/CH4) for reline were found to agree reasonably well with the available literature data, and those for glyceline were found to be the highest with regards to the natural gas sweetening process. In addition, selectivities (SCO2/N2 and SH2S/N2) were also the highest for glyceline in the flue gas treatment application, having values of ∼200 and ∼1354, respectively, at the temperature 298.15 K. Finally, computation of selectivity from the MD simulation provides a screening tool for the selection of solvents for gas-separation processes.