Direct evaluation of void effect on gas permeation in mixed matrix membrane by non-equilibrium molecular dynamics

Abstract

The effect of the void between filler (MFI-type zeolite) and matrix (a polymer of intrinsic microporosity) in the mixed matrix membrane (MMM) on CO2/CH4 gas permeability was investigated at the atomistic scale by non-equilibrium molecular dynamics (NEMD). In our NEMD, the permeation through the void at the interface between the filler and the matrix, the matrix, and the filler were simulated simultaneously. The permeating path was analyzed to clarify the void effect at the interface between the matrix and the filler on permeance and selectivity. NEMD results clearly showed that permeation through the filler and matrix was the fastest that could be expected using the MMM design concept. Furthermore, permeation through the void also showed high CO2 selectivity, although the permeation rate was lower than that through the filler inside and the matrix. The CO2 permeation through the filler and matrix was dominant at about 43% of the total permeance, whereas the permeation through the void was about 40% of the total permeance. This means that the void at the interface significantly influenced the permeability and selectivity. This suggests that controlling the void structure/affinity between the filler and the matrix could drastically improve MMM permeation properties.