Solvent properties of functionalized ionic liquids for CO2 absorption

Ionic liquids can be used as solvents for gas absorption operations in order to improve the process economy and general efficiency of gas separations. This work investigates solvent properties of ionic liquids and compares them to amine solutions used for absorption of carbon dioxide (CO2). The CO2 solubility into imidazolium-based Room Temperature Ionic Liquids (RTILs) was measured at temperatures between 298 and 363 K and pressures up to about 1 M Pa. The study includes measured values of physical properties such as density and viscosity of the RTILs investigated.
The results have shown a remarkable influence of the bulk physical properties of the solvent on the gas absorption rate. The absorption into amine solutions is faster than in ionic liquids at given temperatures due to the relatively high viscosity values of the RTILs. However, the very low vapour pressure and “design character” of the ionic liquids give considerable advantages as a solvent compared to amine solutions. It was possible to increase the ionic liquid volumetric gas load almost threefold by attaching functional groups to the ionic liquid, whereas for the traditional amine solutions the maximum gas load is stoichiometrically limited.