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The production of hydrogen from fossil fuels by steam reforming/water gas shift can be enhanced by separating the reaction byproduct, CO 2 , within the reactor as it is produced. Such a separationenhanced reaction not only has higher conversion efficiency, but can also be considered a greener process which produces high-purity hydrogen with little CO 2 contamination. Supported ionic liquid membranes may be able to achieve this separation task since they are known to have high CO 2 and low H 2 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 CO 2 , H 2 , CO, and CH 4 , in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are compared to one another. In addition, the solubilities of CO 2 and H 2 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 CO 2 /H 2 selectivities.

The high-pressure phase behavior of the binary system CO 2 + 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was determined experimentally by a synthetic method. Bubble points were measured for mixtures of various carbon dioxide concentrations within a temperature and pressure range of (310 to 450) K and (0.5 to 14) MPa, respectively. The results were compared with solubility data obtained by three other research laboratories using different phase equilibria measuring techniques, and good agreement was observed in every case. The effect of the cation alkyl chain length was also investigated by comparing CO 2 solubility in four homologous members of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide family in which the alkyl was either ethyl, butyl, hexyl, or octyl. It was shown that CO 2 solubility increases almost linearly with increasing alkyl chain length.

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