Water Sorption and Diffusivity in [C2C1im][BF4], [C4C1im][OAc], and [C4C1im][Cl

Abstract

Measurements of in situ atmospheric water absorption and desorption in ionic liquids (ILs) (1-ethyl-3-methylimidazolium tetrafluoroborate [C2C1im][BF4], 1-butyl-3-methylimidazolium acetate [C4C1im][OAc], and 1-butyl-3-methylimidazolium chloride [C4C1im][Cl]) were made using a gravimetric microbalance at temperatures ranging from 283.15 to 315.15 K and relative humidity (RH) 0–70% at 101 kPa. Solubility data were well correlated using the nonrandom two-liquid (NRTL) activity model, and time dependent concentration data were used to determine the binary diffusion coefficients using one- and two-dimensional transport models of water in the IL–water systems. The solubility of water was highest in [C4C1im][OAc] (77.5 mol %), followed by [C4C1im][Cl] (68.6 mol %), and [C2C1im][BF4] (19.5 mol %) at equivalent conditions (303.15 K and 25.00% RH). The diffusion coefficients in order of increasing relative humidity ranged from 1.3 × 10–10 to 2.8 × 10–11 m2/s for [C2C1im][BF4], from 8.8 × 10–12 to 3.9 × 10–11 m2/s f...