Prediction of CH4/H2 Mixture Selectivity in Zn(tbip) from Computer Simulations

We have computed CH4/H-2 mixture adsorption isotherms and mixture self-diffusivities in Zn(tbip), a nanoporous metal organic material, at 298 K using grand canonical Monte Carlo and equilibrium molecular dynamics simulations. We calculated the adsorption and diffusion selectivities from our simulation results. An approximate model was used to estimate the maximum membrane selectivities. The adsorption selectivity very strongly favors CH4 over H-2, whereas the diffusion selectivity favors H-2 over CH4. We find that the adsorption selectivity dominates the mixture selectivity, giving values in the range of 6-50 CH4/H-2. This indicates that Zn(tbip) may be useful for separating CH4/H-2 mixtures.