A potential ionic liquid for CO2-separating gas membranes: selection and gas solubility studies

The production of hydrogen from fossil fuels by steam reforming/water gas shift can be enhanced by separating the reaction byproduct, CO2, within the reactor as it is produced. Such a separation-enhanced reaction not only has higher conversion efficiency, but can also be considered a greener process which produces high-purity hydrogen with little CO2 contamination. Supported ionic liquid membranes may be able to achieve this separation task since they are known to have high CO2 and low H2 solubilities. In this study, the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide family of ionic liquids has been selected for this purpose, based on limited literature data. The solubilities of major reaction gases, namely CO2, H2, CO, and CH4, in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are compared to one another. In addition, the solubilities of CO2 and H2 in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are compared. The results indicate, from a thermodynamic point of view, the possibility of using this family of ionic liquids as separation membranes with practical CO2/H2 selectivities.