Free volume in physical absorption of carbon dioxide in ionic liquids: Molecular dynamics supported modeling

Abstract

Understanding the mechanisms underlying the carbon dioxide (CO2) absorption in ionic liquids (ILs) is the key to their efficient utilization in industrial flue gas treatment. One of the parameters considered substantially important in the process is the Free Volume. In this study, the Fractional Free Volume (FFV) of 73 ILs was calculated using Molecular Dynamics (MD). A quantitative Structure-Property Relationship (QSPR) study was then employed to predict the FFV, but the validation parameters were unsatisfactory. In the second part, the importance of Free Volume in the absorption of CO2 in ILs was assessed by creating two models to predict Henry’s Law Constant of CO2 in ILs. It was found that the addition of the FFV parameter considerably improved the statistical parameters and predictability of the QSPR model. Furthermore, FFV was found to be heavily dependent on the cation type and its inclusion allowed for the determination of more subtle molecular interactions.