Thermodynamic Analysis of Ionic Liquids for CO 2 Capture, Regeneration and Conversion

Global warming due to emission of greenhouse gases, especially carbon dioxide (CO2), has a major impact on climate change. A large number of absorbents were tested for CO2 capturing, and the literature reports suggested that ionic liquids (ILs) showed better performance than conventional absorbents. In recent years, several researchers studied experimental and theoretical methods to understand the role of ILs in CO2 capture, regeneration and conversion. ILs have potential to replace conventional absorbents for CO2 capture due to the combination of unique properties and good solvating capability. The physical and chemical properties of ILs could be modified by tuning their ionic mobilities to achieve specific application requirements. Further, CO2 solubility in ILs can be attributed to free volume effect and Lewis acid–base interactions. The significant enhancement in viscosity of IL after CO2 absorption can be controlled by the addition of water as co-solvent, and the presence of water has the potential to compete with the CO2 for absorption. After CO2 absorption, the recycling of ILs is important, which can be performed by heating. From the viewpoint of thermodynamics, the enthalpy change is the main driving force for CO2 absorption for ILs, and other thermodynamic parameters can be derived for this absorption process.