Synergistic effect of filler sieving and polymer rigidification for selective C2H4/C2H6 separation

Membrane separation technology on account of low energy consumption shows great potential for energy-intensive C 2 H 4 /C 2 H 6 separation. Mixed matrix membranes (MMMs), fabricated by embedding sieving functional fillers within polymer, are expected to improve the separation performance of conventional polymer. However, most MMMs fail to deliver the anticipated gains in C 2 H 4 /C 2 H 6 separation selectivity. Sieving fillers typically have ultra-small pores that may impose higher entry barriers on polarizable hydrocarbons than the dynamic free-volume elements of polymers. Thus, focus should extend beyond the filler itself to the structural variations of the polymer matrix upon filler incorporation. In this work, we incorporated an C 2 H 4 /C 2 H 6 sieving metal-organic framework material, Cu(BF 4 ) 2 (4-DPDS) 2 , into 6FDA-DAM to fabricate MMMs for C 2 H 4 /C 2 H 6 separation. It is found that the size sieving ability of Cu(BF 4 ) 2 (4-DPDS) 2 contributes partially to the improved C 2 H 4 /C 2 H 6 diffusion selectivity. Additionally, the rigidification of 6FDA-DAM molecular chains induced by the strong interfacial interaction markedly hinders C 2 H 6 transport. These two factors act synergistically to effectively enhance the C 2 H 4 /C 2 H 6 diffusion selectivity. For an equimolar gas mixture, the filler-optimized MMMs exhibit a C 2 H 4 permeability of 13.35 barrer and a C 2 H 4 /C 2 H 6 selectivity of 7.02, exceeding the separation upper bound reported in 2013 and representing the highest selectivity reported for sieving-filler-based MMMs. This work provides valuable insights for the rational design of high-performance MMMs for ethylene/ethane separation.