(114b) Molecular Simulations and Predictions of Pure and Mixed CO2/H2 Gas Absorption Into Some Ionic Liquids

Classical molecular dynamics and Monte Carlo simulations are used to calculate the self-diffusivity and solubility of pure and mixed gases of CO2, H2, and Ar absorbed into some ionic liquids. For H2 absorption into [hmim][Tf2N], 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 they disagree with those by Noble et al. [ Ind. Eng. Chem. Res. 2008, 47, 3453] and Costa Gomes [ J. Chem. Eng. Data 2007, 52, 472]. Simulations for H2 absorption into another ionic liquid of [bmim][PF6] also agree with the experimental data obtained by Maurer et al. The interaction between H2 and [hmim][Tf2N] is very weak, about three times smaller than Ar, and six times smaller than CO2. These results are consistent with a decreasing order in the solubility from CO2 to Ar and to H2. The molar volume of the ionic liquid is found to be the determining factor for the H2 solubility. The simulated permeability values for CO2 and H2 in [hmim][Tf2N] are clsoe to the experimental data by Luebke et al. [J. Membr. Sci. 2007, 2008].

Based on our simulations, we propose to seacrh for ionic liquids with small molar volume leading to low H2 solubility, but still having high CO2 solubility through non-physical interaction for the CO2/H2 separation. We have identified several ionic liquids and they are predicted to show high CO2/H2 selectivity.