Thermodynamic and molecular insights into the absorption of H₂S, CO₂, and CH₄ in choline chloride plus urea mixtures

Abstract

Abstract Deep eutectic solvents (DESs) are a class of promising media for gas separation. In order to examine the potential application of DESs for natural gas upgrading, the solubilities of H 2 S, CO 2 , and CH 4 in choline chloride (ChCl) plus urea mixtures were measured in this work. The solubility data were correlated with Henry's law equation to calculate the thermodynamic properties of gas absorption processes, such as Henry's constants and enthalpy changes. Grand‐canonical Monte Carlo simulations and quantum chemistry calculations were also performed to examine the mechanism of gas absorption processes. It is found that the absorption of H 2 S in ChCl + urea mixtures is governed by the hydrogen‐bond interaction between Cl of ChCl and H of H 2 S, whereas the absorption of CO 2 and CH 4 in ChCl+urea mixtures is governed by the free volume of solvents. Based on the different behavior of gas absorption, high H 2 S/CO 2 , H 2 S/CH 4 , and CO 2 /CH 4 selectivities can be achieved by adjusting the ratio of ChCl/urea in mixtures.