Absorption of carbon dioxide in ionic liquids and their mixtures

Abstract

The potential application of some ionic liquids and of binary mixtures of them as absorbents for CO2 has been investigated. The CO2 absorption capacity of these solvents has been experimentally determined in the low pressure range. Several mixtures of two CO2- physisorbing ionic liquids, and of a CO2-physisorbing ionic liquid with a CO2-chemisorbing ionic liquid, have been analysed. Although their absorption capacities generally lie within those of the corresponding pure ionic liquids, different synergistic effects have been found. These effects are accompanied by the tuning of thermal behaviour and physical properties with variation of the composition of the mixtures. The results are discussed in terms of the mechanisms of absorption and the influence of the structural features of the ionic liquids. Suitable correlations of the experimental data for both the CO2 absorption isotherms and the physical properties investigated (density, viscosity, and surface tension) have been carried out. In a further aspect, the CO2 absorption capacity of a highly viscous amino acid ionic liquid has been substantially improved, along with its thermal stability, by supporting it onto mesoporous silica.