Diffusion of CH4 and H2 in ZIF-8

Initiated by separation factors of up to 15 between CH4 and H2 found in experiments of gas mixture permeation through a newly developed ZIF-8 membrane the diffusion of CH4 and H2 in ZIF-8 has been investigated by IR microscopy and molecular dynamics simulations. Several well known interaction parameter sets for simulations have been tested. It turned out that the H2/CH4-ZIF-8 system is very sensitive with respect to the choice of these parameters. The large differences in the diffusion behavior of CH4 and H2 are investigated by microscopic simulation tools and compared with experiments. A parameter set has been found that gives reasonable agreement with experimental IR and membrane permeation results.

► First molecular dynamics simulations of a fully flexible ZIF-8.
► Inclusion of lattice flexibility proves to be absolutely necessary.
► Reasonable agreement between simulation and experimental measurements is obtained.