(103b) Simulations and Experimental Studies of CO2 and H2 Separation Using Ionic LIquids

Classical molecular dynamics, Monte Carlo simulations, and ab initio calculations are used to to study pure and mixed gases containing CO2, H2, and Ar in several ionic liquids. For H2 absorption into [hmim][Tf2N] and [bmim][PF6] the computed isotherms, Henry's law constants, and partial molar enthalpies agree very well with the experimental data obtained by Maurer et al. [J. Chem. Eng. Data 2006, 51, 1364], however these data disagree with those of Noble et al. [ Ind. Eng. Chem. Res. 2008, 47, 3453] and Costa Gomes [ J. Chem. Eng. Data 2007, 52, 472]. The simulated solubility for H2 absorbed in [hmim][Tf2N] alo agree with our experimental data. The interaction between H2 and the [hmim][Tf2N] ionic liquid was found to be very weak, about three times smaller than Ar and six times smaller than CO2 for the same ionic liquid. These results are consistent with a decreasing order in the solubilities from CO2 to Ar and to H2. The molar volume of the ionic liquid was found to be the determining factor for H2 solubility. The simulated permeability values for CO2 and H2 in [hmim][Tf2N] are about 0.8-3 times the experimental values obtained by Luebke et al. [J. Membr. Sci. 2007, 2008]. Based on the simulations, we propose to separate CO2 and H2 using ionic liquids with small molar volume (low solubility for H2) but still exhibiting a high enough solubility for CO2 through strong intercations. One example of a candidate ionic liquid, NETL-ILA, has been identified from simulations to show high CO2 permeability and high CO2/H2 selectivity. The experimental H2 permeability in NETL-ILA at 37°C is found to be very low while the CO2/H2 selectivity is high, in very good agreement with the predicted values from simulations.