Physical Property and Free Volume Correlations of Highly-Branched Alkylimidazoles for Gas Separations

Previous work has characterized specific physical properties and CO2 solubility of 1-n-alkylimidazole solvents for use in pre- and post-combustion CO2 capture during gas treating.  This research project explores the CO2 solubility and physical properties of multiply-branched alkylimidazole solvents to determine the effects of functional group position(s) on various chemical and physical attributes.  Using this information, additional correlations between ring substitution and physical properties can be derived to optimize the characteristics. Synthesis and purification of these compounds were followed by tests to determine density, viscosity, and vapor pressure as functions of temperature and ring substitution, and these properties were shown to be comparable to previously-tested 1-n-alkylimidazoles.  The solvents in general were found to have low viscosities (<15 cP) and negligible vapor pressures (<0.5 mbar).  CO2 solubility experiments also showed that multiply-branched alkylimidazoles have similar if not improved absorption capacities relative to ionic liquids and 1-n-alkylimidazoles.  In future work, polymeric membranes can be synthesized from these compounds to determine CO2 permeability and selectivity as a function of ring substitution.  The ultimate goal of this research is to find an imidazole-based solvent with low volatility and high CO2 absorption capacity or an imidazole-based membrane structure with high CO2 permeability and selectivity that can be easily manufactured for application in large-scale industry for the reduction of atmospheric CO2 emissions.