High pressure solubility of CH4, N2O and N-2 in 1-butyl-3-methylimidazolium dicyanamide: Solubilities, selectivities and soft-SAFT modeling

Abstract

The society and industry commitment to progressively reduce Green House Gases (GHGs) emissions forged important challenges that conventional gas separation processes are unable to overcome. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade as a promising class of viable solvents to capture pollutants and for gas separation processes. Being the IL-based membranes gas separation controlled by the gas solubility in the IL rather than by its diffusivity, the solubility of gases in ILs stands as highly relevant input for their application in liquid membranes. As part of a continuing effort to develop an IL based process for high pressure capture of GHGs, the phase equilibria of nitrous oxide (N2O), methane (CH4) and nitrogen (N-2) were investigated in this work. Experimental gas-liquid equilibrium data for N2O, CH4 and N-2 in [C4C1 im][N(CN)(2)] were determined in the (293 to 363) K temperature range, for pressures up to 70 MPa and gas mole fractions up to 35 %. Unfavorable interactions towards the studied gases, with positive deviations to ideality, were observed for all the studied gases, placing the studied IL among those with the lowest selectivities reported. The observed behavior highlights that a delicate balance between the solvent polarity and its molar volume must be ascertained when a highly selective solvent for N-2 or CH4 separation is envisaged. The soft-SAFT EoS successfully described the high pressure phase behavior data using the molecular model and parameters sets reported in previous works. A good description of the binary systems studied, including the small CH4 temperature dependency and the N-2 reverse temperature dependency on the solubility were achieved using just one binary interaction parameter. This reinforces the use of soft-SAFT as an accurate model to describe the behavior of gases in ILs for different applications. (C) 2015 Elsevier B.V. All rights reserved.