Effect of water on high-pressure ternary phase equilibria of CO2 + H2O + alkanolamine based ionic liquid

Abstract

Some ethanolamine or hydroxylammonium based ionic liquids have shown great potential in CO2 separation processes. However, not much is known about the influence of water on the CO2 solubility of these liquids. In this paper, we study the high-pressure ternary liquid-vapor phase equilibria. The systems were composed of carbon dioxide, water, and an alkanolamine based IL: N-methyl-2-hydroxyethylammonium propionate [m-2HEA] [Pr]. We studied systems whose water contents varied from 6.7% to 52.5%, temperatures from 313 K to 353 K, and pressures from 0.6 MPa up to 22 MPa.The phase equilibria experiments showed that the amount of ionic liquid in the mixture controls the solubilization of CO2 and is not significantly affected by changes in the water content within the studied range. These data were simulated from a molecular point of view using the Gibbs ensemble Monte Carlo method. A force field was estimated to describe the Ionic Liquid (IL) density at a wide range of water content values using the isothermal-isobaric Monte Carlo (NPT-MC). The calculated densities presented a good agreement with experimental data, indicating that the proposed force field parameters are suitable to describe the densities of the IL mixtures and, therefore, can be used to simulate the ternary phase equilibria. The software package CassandraV1.2 was employed to simulate the ternary phase equilibria, resulting in reasonably low deviations when compared to the experimental data. However, the predicted solubility of carbon dioxide in N-methyl-2-hydroxyethylammonium propionate [m-2HEA][Pr] was slightly higher when compared with the experimental values. (C) 2020 Elsevier B.V. All rights reserved.