Diffusivities of Gases in Room-Temperature Ionic Liquids:  Data and Correlations Obtained Using a Lag-Time Technique

Diffusivity and solubility data are presented for carbon dioxide, ethylene, propylene, 1-butene, and 1,3-butadiene in five imidazolium-based ionic liquids and one phosphonium-based ionic liquid covering a liquid viscosity range of 10−1000 cP. The data were obtained using a lag-time technique that involves analysis of both the transient and steady-state permeation regimes through a supported liquid film. In general, gas diffusion in ionic liquids (∼10 -6 cm 2 /sec) is slower than that in traditional hydrocarbon solvents and water, but the dependence on viscosity is lower. Conversely, the dependence of diffusivity on temperature and the size of the solute gas is higher than that for nonpolar solvents. A correlation for gas diffusivity in ionic liquids at 30 °C is proposed in terms of the gas molar volume, the ionic liquid viscosity, and density, based on 30 data points with a coefficient of multiple determination r 2 = 0.975.