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 (N-2) in 1-ethyl-3-methylimidazolium methyl-phosphonate ([C(2)mim][CH3OHPO2]) were studied in this work. Experimental measurements for the CO2, N2O, CH4 and N-2 solubilities in [C(2)mim][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 N-2, 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/N-2 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 [C(2)mim][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. (C) 2013 Elsevier Ltd. All rights reserved.
keywords
TEMPERATURE IONIC LIQUIDS; EQUATION-OF-STATE; DIRECTIONAL ATTRACTIVE FORCES; GLYCOL MONOMETHYL ETHER; THERMODYNAMIC PERTURBATION-THEORY; CARBON DIOXIDE SOLUBILITIES; ASSOCIATING FLUID THEORY; LENNARD-JONES CHAINS; SOFT-SAFT EQUATION; PHASE-BEHAVIOR
subject category
Science & Technology - Other Topics; Energy & Fuels; Engineering
authors
Pereira, LMC; Oliveira, MB; Dias, AMA; Llovell, F; Vega, LF; Carvalho, PJ; Coutinho, JAP
our authors
acknowledgements
The authors are thankful for financial support from Fundacao para a Ciencia e a Tecnologia (Project PTDC/EQU-FTT/102166/2008), Laboratorio Associado Centro de Investigacao em Materiais Ceramicos e Compositos (Project Pest-C/CTM/LA0011/2013), Post-Doctoral grants of Pedro J. Carvalho (SFRH/BPD/82264/2011), Mariana B. Oliveira (SFRH/BPD/71200/2010) and Ana M.A. Dias (SFRH/BPD/40409/2007). F. Llovell acknowledges a TALENT contract from the Catalan Government. Additional financial support was provided by the Spanish government, Ministerio de Economia y Competitividad (projects CTQ2008-05370/PPQ and CENIT SOST-CO2 CEN2008-01027) and the Catalan government (project 2009SGR-666). Support from Carburos Metalicos, Air Products Group, is also acknowledged.