Molecular understanding of pyridinium ionic liquids as absorbents with water as refrigerant for use in heat pumps

Abstract

Aiming at developing new absorbent/refrigerant working pairs for heat pumps, thermodynamic and transport properties of two pyridinium ionic liquids (ILs), N‐ethylpyridinium bis(trifluoromethanesulfonyl)amide and N‐ethylpyridinium trifluoromethanesulfonate were studied using molecular simulation and nuclear magnetic resonance techniques. The microscopic structure of the ILs and the solvation environment of water, including hydrogen bonding, were studied. Free‐energies of solvation of water were obtained using perturbation methods, and the values agree with experimental observations. Self‐diffusion coefficients and viscosity were computed and compared with nuclear magnetic resonance measurements and literature. Simulations predict slower dynamics when compared with experiment: diffusion coefficients are underpredicted, whereas viscosity is overpredicted. As such, simulation is consistent in a Stokes‐Einstein sense. The trends in transport properties due to changing anion, to the presence of water and the effect of temperature are well predicted. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3523–3531, 2017