There has been considerable interest in developing technologies for carbon dioxide separations using room temperature ionic liquids. The development of new separation processes requires an understanding of the solubility and diffusivity of target gases in these unique liquids. Recent work in our lab has focused on measurements of carbon dioxide solubility and diffusivity using a gas uptake technique. In this approach, the decrease in carbon dioxide pressure above a thin ionic liquid film is monitored as carbon dioxide permeates into the ionic liquid film. Pressure versus time data are related to the Henry's Law constant and diffusivity using a one-dimensional transport model. Results collected with a number of different ionic liquids at temperatures ranging from 10oC to 40oC will be presented. The role played by the anion and the cation in both solubility and diffusivity will be discussed. A correlation relating carbon dioxide diffusivity to ionic liquid properties will also be presented.

Higher permeability of carbon dioxide is a necessary requirement for ionic liquid selection for carbon dioxide separation. The Permeability of a gas is a function of both diffusivity and solubility. The results from these measurements have also been used to examine choice of ionic liquids for carbon dioxide separation. Results show that ionic liquids with the best carbon dioxide solubility have slower diffusion coefficient. A comparison of selectivity estimations based on these solubility and diffusivity measurements to membrane permeability measurements performed using a supported ionic liquid membrane support this conclusion.

References:

1. Ying Hou and Ruth Baltus, Ind .Eng. Chem. Res, 46, 8166, 2007