Water sorption equilibrium on 2-hydroxyethyl-trimethylammonium acetate in the temperature range 298.25–349.55K

Ionic liquids (ILs) have emerged as novel sorption materials capable to achieve exceptional water vapour uptake that is attractive for their use in heat transformation technologies. Water sorption equilibria on 2-hydroxyethyl-trimethylammonium acetate or choline acetate ([Cho][OAc]) were measured at eight different temperatures: 298.25, 303.25, 308.35, 318.55, 328.75, 333.85, 344.15 and 349.55 K. Equilibrium measurements were performed with a dynamic vapour sorption (DVS) system. With a relative humidity of around 90% a water uptake larger than 3.5 g_W g_IL⁻¹ was observed for all the temperatures. The resulting type III isotherms were correlated with the Guggenheim-Anderson-de Boer (GAB) model as well as the Redlich-Kister (RK) excess Gibbs energy model. It was found that both models fit the experimental data with great accuracy and provide an appropriate description of the water sorption equilibria. The regressed parameters of the RK model were also employed to predict excess properties of the binary system. Moreover, a thermodynamic cycle was assessed and compared with sorbent benchmarks, highlighting a performance that makes the choline acetate/water pair a viable option in sorption chiller applications.