Properties and Performance of Ether-Functionalized Imidazoles as Physical Solvents for CO₂ Separations

Abstract

Previously, we investigated 1-n-alkylimidazoles as low viscosity, low vapor pressure physical solvents for CO2/CH4 separation and noted a decrease in performance as the length of the n-alkyl chain was extended. Here, we examine imidazoles featuring oligo(ethylene glycol) substituents (“PEG n -imidazoles”) as an opportunity to improve upon the separation performance of this class of molecules. In the current work, we have characterized the density and the viscosity of PEG n -imidazoles over the temperature range 20–80 °C. PEG n -imidazoles are slightly more viscous than 1-n-alkylimidazoles but still fall below 20 cP. Ideal gas solubilities of CO2 and CH4 were measured in PEG n -imidazoles at gas partial pressures of ∼5 bar and temperatures of 25–70 °C. Solubilities of CO2 and CH4 were both found to decrease with increasing temperature, with a stronger dependence for CO2. However, better CO2/CH4 selectivity was achieved in PEG n -imidazoles at lower operating temperatures than was observed for 1-n-alkylimidazoles. Physical properties and gas separation performances were correlated with fractional free volume calculated via COSMOtherm, as well as solubility parameters. The results show trends of decreased FFV when polar ether groups comprise the substituent, and that CO2 solubility and solubility selectivity for CO2/CH4 are improved compared to their nonpolar, hydrocarbon-based analogues.

Absorption degree analysis on biogas separation with ionic liquid systems

“…The CH 4 solubility decreases 15% on average from 303 to 323 K, while the value is 30% for the CO 2 solubility at the same temperature range. Similar observation has also been mentioned in the literature (Shannon et al, 2011(Shannon et al, , 2013.…”

Effect of branched and cycloalkyl functionalities on CO2 separation performance of poly(IL) membranes

“…Optimized structures of the cations were developed by our research group with TURBOMOLE, using the TZVP basis set [51] with the Becke and Perdew (b-p) functional [52,53] at the density functional theory (DFT) level [52][53][54]. All COSMO calculations were also performed with TZVP, which is consistent with other works that have utilized COSMOTherm to predict the properties of ILs and other types of molecules [55][56][57][58][59].…”

Aqueous hydrazine as a promising candidate for capturing carbon dioxide

“…Numerous sorbents have been developed for postcombustion CO 2 capture, which include alkanolamines (Rochelle, 2009;Rodriguez et al, 2011;Bishnoi and Rochelle, 2002;Rainbolt et al, 2011;Faramarzi et al, 2009), diamines (Zhou et al, 2010;Speyer et al, 2010), chilled ammonia (Peltier, 2008;Darde et al, 2010), CO 2 -binding organic liquids Zhang et al, 2013;Mathias et al, 2013), non-amine based solvents (Li et al, 2005;Chang et al, 2013), ionic liquids (Bates et al, 2002;Bara et al, 2009;Shannon et al, 2013), and phase-changing sorbents (Perry et al, 2010(Perry et al, , 2012. Monoethanolamine (MEA) has been the most extensively studied solvent for CO 2 capture applications (Rochelle, 2009;Liu et al, 1999;Freguia and Rochelle, 2003;Fan et al, 2009;Conway et al, 2011;Han et al, 2011;Zhu et al, 2012;Supap et al, 2001).…”