Task-specific ionic liquids for efficient ammonia absorption

A computational-experimental study was carried out to select ionic liquids with optimized properties for absorption of ammonia (NH3). Firstly, a quantum-chemical COSMO-RS analysis was performed to analyze the solute–solvent intermolecular interactions determining the gas–liquid equilibrium data. Subsequently, a rational COSMO-RS screening of Henry’s law coefficient of NH3 over 272 ionic liquids was done to select potential high-capacity ammonia solvents. Finally, further experimental studies were carried out to evaluate the suitability of selected ILs as NH3 absorbents, in terms of thermal stability, liquid-phase window and ammonia solubility. Experimentally was demonstrated that both absorption and desorption proceed quite rapidly and complete desorption was achieved at room temperature. From the results obtained we propose two commercially available task-specific ILs, [EtOHmim][BF4] and [choline][NTf2], whose characteristics would allow using new easy-to-regenerate NH3 absorption systems operating in absorption–desorption cycles at near-ambient temperature and atmospheric pressure.

► In this study we propose optimized ionic liquids (ILs) for ammonia absorption.
► COSMO-RS method is applied to analyze the solute–solvent interactions.
► A computational screening is conducted to select high-capacity ammonia IL absorbents.
► NH3 solubility and other properties are experimentally evaluated for selected ILs.
► Two task-specific ILs are proposed for easy-to-regenerate NH3 absorption systems.