International Journal of Greenhouse Gas Control 19 (2013) 299–309 Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control j ourna l h o mepage: www.elsevier.com/locate/ijggc High pressure separation of greenhouse gases from air with 1-ethyl-3-methylimidazolium methyl-phosphonate Luís M.C. Pereira a , Mariana B. Oliveira a , Ana M.A. Dias b , Felix Llovell c , Lourdes F. Vega c,d , Pedro J. Carvalho a , João A.P. Coutinho a,∗ a CICECO, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal b CIEPQPF, Departamento de Engenharia Química, FCTUC, Universidade de Coimbra, Rua Sílvio Lima, Pólo II – Pinhal de Marrocos, 3030-790 Coimbra, Portugal c MATGAS Research Center (Carburos Metálicos/Air Products, CSIC, UAB), Campus UAB, 08193 Bellaterra, Barcelona, Spain d Carburos Metálicos/Air ProductsGroup, C/ Aragón, 300, 08009 Barcelona, Spain a r t i c l e i n f o Article history: Received 21 December 2012 Received in revised form 4 September 2013 Accepted 9 September 2013 Keywords: Ionic liquids Gas solubilities soft-SAFT modeling Henry’s constant Selectivities a b s t r a c t 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 (CO 2 ), nitrous oxide (N 2 O), methane (CH 4 ) and nitrogen (N 2 ) in 1-ethyl-3-methylimidazolium methyl-phosphonate ([C 2 mim][CH 3 OHPO 2 ]) were studied in this work. Experimental measurements for the CO 2 , N 2 O, CH 4 and N 2 solubilities in [C 2 mim][CH 3 OHPO 2 ] 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 N 2 , CH 4 and CO 2 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 CO 2 /N 2 or CO 2 /CH 4 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 N 2 O and [C 2 mim][CH 3 OHPO 2 ], 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. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Several sources, anthropogenic or of natural origin, contribute to the emission of several greenhouse gases into the atmosphere, with burning of fossil fuels and industrial processes having the highest negative impact. Among several post-combustion cap- ture and natural gases treatment processes currently available to reduce these emissions, such as membrane-based separations and physical and chemical sorbents adsorption, the amines and ∗ Corresponding author. Tel.: +351 234 401 507; fax: +351 234 370 084. E-mail address: jcoutinho@ua.pt (J.A.P. Coutinho). ammonia absorption processes maintain a prominent position, with most of the industrial plants using chemical absorption pro- cesses with monoethanolamine (MEA)-based solvents. Although modified to incorporate inhibitors, that reduce solvent degradation and equipment corrosion, the MEA-based processes still present several disadvantages, such as large equipment sizes, due to low amines/water weight relation, high solvent regeneration costs and loss of solvent by evaporation, to mention just a few (Olajire, 2010). Furthermore, limitations on the existing control methods and on the industrial processes require the development of new methods and processes, to reduce the pollutants level. Among all greenhouse gases, carbon dioxide (CO 2 ) nitrous oxide (N 2 O) and methane (CH 4 ) are the most abundant and, hence, with 1750-5836/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijggc.2013.09.007