High pressure separation of greenhouse gases from air with 1-ethyl-3-methylimidazolium methyl-phosphonate

Abstract

Increasing pollutants emissions, along with the limitations present on the existing control methods and stricter legislation to come, demand the development of new methods to reduce them. Ionic liquids (ILs) have been attracting an outstanding attention during the last decade and rose as a promising class of viable solvents to capture pollutants and for gas separation processes. As part of a continuing effort to develop an ionic liquid based process for high pressure capture of greenhouse gases, the phase equilibria of carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and nitrogen (N2) in 1-ethyl-3-methylimidazolium methyl-phosphonate ([C2mim][CH3OHPO2]) were studied in this work.Experimental measurements for the CO2, N2O, CH4 and N2 solubilities in [C2mim][CH3OHPO2] were carried out for gases mole fractions ranging from (0.018 to 0.504), in the temperature range (293.23 to 363.34)K and for pressures from (1.16 to 87.61)MPa.The particular behavior of the selected highly polar ionic liquid is here shown for the first time through the reported experimental data. The low N2, CH4 and CO2 solubilities, with the later system presenting positive deviations to ideality, show the ionic liquid unfavorable interactions with the studied gases and the necessity to find a proper compromise between the solvent polarity and its molar volume in order to achieve high CO2/N2 or CO2/CH4 separation selectivities.The good soft-SAFT EoS performance in describing the thermophysical properties of ionic liquids and the phase equilibria of their mixtures with gases was extended in this work for the description of the experimental data reported. New and reliable molecular schemes for N2O and [C2mim][CH3OHPO2], not yet studied within the soft-SAFT framework, were proposed. Using no more than one binary interaction parameter, the soft-SAFT EoS is able to take into account the particular pressure and temperature behavior of the different gases solubilities in the selected ionic liquid. This empowers the equation to be reliably used for other similar systems, as tool to optimize the given process, searching for the best conditions for capture.