High pressure vapor-liquid equilibria for binary methane and protic ionic liquid based on propionate anions

Sour gases and methane separation has been studied for many years and ionic liquids (ILs) could be used to promote their separation. Protic ionic liquids based on substitute amines and carboxilate anions were reported to be selective to methane/carbon dioxide separation. However, the methane + ILs phase equilibria data, which is required to design gas separation, are scarce on the open literature. This study report the high pressure phase transition data for methane + N-methyl-2-hydroxyethylammonium propanoate, bis(2-hydroxyethyl)ammonium propanoate, or 2-hydroxyethylammonium propanoate. The binary system methane + N-methyl-2-hydroxyethylammonium propanoate was compared to literature experimental data. The structures and purities of ILs were confirmed by 1H NMR, 13C NMR, HSQC and HMBC NMR studies. Water content were measured by Karl Fischer coulometer measurements. The phase transitions have been classified as bubble points and studied at four temperatures from 333.1 to 363.1 K and pressures from 4 to 16 MPa. The experimental data were obtained using the static-synthetic visual method by a variable-volume cell unit. VLE transitions have been classified as bubble points. Henry's law constants were estimated and compared with other ILs and organic solvents. Experimental data for CH4 + + N-methyl-2-hydroxyethylammonium propanoate system were correlated using the three-parametric Redlich - Kwong - Peng - Robinson equation of state (RKPR-EoS) coupled to cubic van der Waals mixing rules (regarding the composition) and temperature dependence for the interaction energy parameter (CMR-T).