Molecular Simulation Study of CH4/H2 Mixture Separations Using Metal Organic Framework Membranes and Composites

Grand canonical Monte Carlo and equilibrium molecular dynamics simulations have been used to compute adsorption isotherms and self-diffusivities of CH4/H-2 mixtures in a nanoporous metal organic framework, Zn(bdc)(ted)(0.5), at room temperature for various compositions. Adsorption-based selectivity, ideal selectivity, and mixture selectivity of Zn(bdc)(ted)(0.5) membranes for separation of CH4/H-2 mixtures are predicted and compared. Performance of several composite membranes including Zn(bdc)(ted)(0.5) as Filler particles in polymer matrixes is examined for separation of H-2 from CH4 using a combination of atomistic and continuum modeling. Results show that Zn(bdc)(ted)(0.5) exhibits higher adsorption-based selectivity and mixture selectivity for CH4 compared to widely studied isoreticular metal organic frameworks. Predictions of permeation models showed that using Zn(bdc)(ted)(0.5) in high-performance composite membranes as tiller particles greatly enhances permeability of H-2 compared to pure polymeric membranes without lowering the selectivity. Even a small volume fraction of Zn(bdc)(ted)(0.5) is enough to carry the composite membranes made of polymers and this metal organic framework (MOF) above the current upper bound established for available polymeric membranes.