Thermodynamic and molecular insights into gas drying with ionic liquid − based mixed absorbents

Abstract

The suitability of mixed solvents of triethylene glycol (TEG) and ionic liquids (ILs) as gas drying agents was first systematically studied from the phase equilibrium to molecular perspectives. The vapor − liquid equilibrium (VLE) for mixed systems of H2O − TEG, H2O − [EMIM][Tf2N], and H2O − TEG − [EMIM][Tf2N] were experimentally measured and predicted using the UNIFAC-Lei model. The results showed that the UNIFAC-Lei model can be successfully extended to predict VLE from binary to ternary systems. In addition, the vapor pressures of H2O − TEG are lower than those of H2O − [EMIM][Tf2N], while the addition of TEG into H2O − [EMIM][Tf2N] can significantly reduce vapor pressure. Molecular dynamic (MD) simulations demonstrate the relationship between the VLE behaviors and microscopic mechanisms of H2O − TEG − [EMIM][Tf2N] and further validate the suitability of TEG − [EMIM][Tf2N] as desiccants due to hydrogen bond (HB) interactions presented in H2O − TEG, H2O − [EMIM][Tf2N] and TEG − [EMIM][Tf2N]. This study provides theoretical guidance for the application of IL-based mixed absorbents in gas drying processes.