Vapor–liquid equilibria of ammonia + ionic liquid mixtures

Solubilities of ammonia in room-temperature ionic liquids, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium ethylsulfate, and N,N-dimethylethanolammonium acetate have been measured for the first time. Static phase equilibrium cells used in our previous work have been slightly modified for the present solubility measurements. Six mixture compositions of each binary system were prepared for the present experiments from about 30 to 85 mol% of ammonia. Pressure–temperature–composition (PTx) data were measured at isothermal conditions of about 283, 298, 323, 348, and 373 K. Observed solubilities in the present ionic liquids are again very high, being similar to our previous report on ammonia + ionic liquid mixtures and all cases show negative deviations from ideal solution behavior. Experimental PTx data have been successfully correlated with our equation-of-state (EOS) model. All the excess properties (enthalpy, entropy, and Gibbs energy) show negative values, indicating some intermolecular complex formation between ammonia and ionic liquids. Application of the present systems to the absorption cooling–heating cycle has also been discussed.