(367d) Time-Dependent Diffusion and Chemical Exchange in Mixtures of An Amine-Functionalized Ionic Liquid and Carbon Dioxide By NMR

Task-specific ionic liquids (TSILs) containing amine functional groups are promising materials for carbon dioxide capture. In this work a novel diffusion NMR technique, which combines advantages of high magnetic field and high magnetic field gradients, was applied to investigate self-diffusion in mixtures of an amine-functionalized TSIL and carbon dioxide. The measured diffusion data reveal time-dependent diffusivities of carbon dioxide in the mixtures on the millisecond time scale. This dependence was attributed to the existence of chemical exchange of carbon dioxide, i.e. exchange of carbon dioxide between the chemisorbed and physisorbed states in the mixtures under conditions of diffusion studies.  At the same time, ion diffusivities were found to be diffusion time independent. High field exchange NMR was used to confirm the existence of the chemical exchange process and to obtain the mean residence times of carbon dioxide in the chemisorbed and physisorbed states. The diffusion and exchange NMR studies were performed for different molar ratios of carbon dioxide and at different temperatures. The experimental results will be compared with the predictions of computer simulations performed for the same or similar mixtures of TSIL and carbon dioxide.