Hydrogen purification is a highly important industrial process, and particularly so as a future renewable-energy carrier. In the recent Science magazine, Lin et al. [Plasticization-enhanced hydrogen purification using polymeric membranes. Science, 2006;311:639-42], reported efficient hydrogen purification (CO2/H-2 separation) using novel polymeric membranes. The selectivity ranges from about 10 to 30 under typical operating conditions. We report here a much higher selectivity (about 30-300) for CO2/H-2 separation using room-temperature ionic liquid solvents. Actual quantitative predictions for such gas-separations have been made for the first time using our equation-of-state model, which was developed in this study and verified experimentally. The present results will provide useful information for far less energy-intensive distillation methods, as well as possible pressure swing adsorption techniques since ionic liquids are essentially non-volatile and can be regarded, from the point of view of sorbents, as "solid" materials. (c) 2006 Elsevier Ltd. All rights reserved.