Separation Selectivity of CH4/CO2 Gas Mixtures in the ZIF-8 Membrane Explored by Dynamic Monte Carlo Simulations.
2020
Here we report a series of nonequilibrium
dynamic Monte Carlo simulations
combined with dual control volume (DCV-DMC) to explore the separation
selectivity of CH4/CO2 gas mixtures in the ZIF-8
membrane with a thickness of up to about 20 nm. Meanwhile, an improved
DCV-DMC approach coupled with the corresponding potential map (PM-DCV-DMC)
is further developed to speed up the computational efficiency of conventional
DCV-DMC simulations. Our simulation results provide the molecular-level
density and selectivity profiles along the permeation direction of
both CH4 and CO2 molecules in the ZIF-8 membrane,
indicating that the parts near membrane surfaces at both ends play
a key role in determining the separation selectivity. All densities
initially show a sharp increase in the individual maximum within the
first outermost unit cell at the feed side and follow a long fluctuating
decrease process. Accordingly, the corresponding selectivity profiles
initially display a long fluctuating increase in the individual maximum
and follow a sharp decrease near the membrane surface at the permeation
side. Furthermore, the effects of feed composition, temperature, and
pressure on the relevant separation selectivity are also discussed
in detail, where the temperature has a greater influence on the separation
selectivity than the feed composition and pressure. More importantly,
the predicted separation selectivities from our PM-DCV-DMC simulations
are well consistent with previous experimental results.
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