High pressure vapor-liquid equilibria for binary carbon dioxide and protic ionic liquid based on ethanolamines + butanoic acid

Abstract

High pressure phase equilibria data were measured for 3 protic ionic liquids and CO2. The studied ILs were based on ethanolamine cations and butanoate anions: 2-hydroxyethylammonium butanoate [2HEA][Bu]; N-methyl-2-hydroxyethylammonium butanoate [m-2HEA][Bu] and N-ethyl-2-hydroxyethylammonium butanoate [e−2HEA][Bu]. This ILs were chosen in order to study the effect of the alkyl growth, from central amine, on CO2 solubility. Water content, FT-IR, 1H and 13C NMR analysis were performed on samples. Charge profiles were also estimated by the geometrical and energetic optimization of ILs structures. The data were correlated with three models: Carvalho and Coutinho predictive empirical correlation; Peng-Robinson EoS; Peng-Robinson EoS coupled with Wong-Sandler/NRTL or two parameters mixing rules; Predictive ternary PC-SAFT model. The results showed that the increase of the carbon chain length, bonded to the amine group, promotes higher CO2 solubility at medium-high pressures but lower CO2 solubility at low pressures. Henry's law constants were also compared to other ILs ones.