New Insights On Transport Properties of Mixtures of Ionic Liquids and Carbon Dioxide by NMR

Ionic liquids (ILs) show great promise as a media for separation of carbon dioxide because CO₂ solubility in ILs is usually quite high. Functionalized ILs were recently developed to achieve an additional dramatic enhancement in carbon dioxide solubility. Detailed understanding of transport properties of mixtures of ILs and carbon dioxide is of large importance for the development of applications of ILs in carbon dioxide storage and separation. In this work pulsed field gradient (PFG) NMR method at high field (17.6 T) and high gradients (up to 30 T/m) was applied to study diffusion in mixtures of ILs and carbon dioxide. Our results demonstrate that carbon-13 PFG NMR can be successfully used to obtain records of carbon dioxide and ion diffusivities in ionic liquid/CO₂ mixtures. This technique was employed in addition to proton PFG NMR, which is a more traditional approach for studies of transport in ILs by NMR. The diffusion data recorded for the mixtures will be compared with those obtained for the corresponding pure ionic liquids. Molecular dynamics simulations were also performed for pure ILs and various IL-CO₂ mixtures at experimental conditions to determine the self-diffusivities of ionic species and CO₂. All the experimental results will be discussed in relation with the corresponding molecular simulation results.