Poly(amide-6-b-ethylene oxide)/[Bmim][Tf2N] blend membranes for carbon dioxide separation

Abstract

Poly(amide-6-b-ethylene oxide) (Pebax1657)/1-butyl-3-methylimidazo-lium bis[trifluoromethyl)sulfonyl]-imide ([Bmim][Tf2N]) blend membranes with different [Bmim][Tf2N] contents were prepared via solution casting and solvent evaporation method. The permeation properties of the blend membranes for CO2, N2, CH4 and H2 were studied, and the physical properties were characterized by differential scanning calorimeter (DSC) and X-ray diffraction (XRD). Results showed that [Bmim][Tf2N] was dispersed as amorphous phase in the blend membranes, which caused the decrease of Tg (PE) and crystallinity (PA). With the addition of [Bmim][Tf2N], the CO2 permeability increased and reached up to approximately 286 Barrer at 40 wt% [Bmim][Tf2N], which was nearly double that of pristine Pebax1657 membrane. The increase of CO2 permeability may be attributed to high intrinsic permeability of [Bmim][Tf2N], the increase of fractional free of volume (FFV) and plasticization effect. However, the CO2 permeability reduced firstly when the [Bmim][Tf2N] content was below 10 wt%, which may be due to that the small ions of [Bmim][Tf2N] in the gap of polymer chain inhibited the flexibility of polymer chain; the interaction between Pebax1657 and [Bmim][Tf2N] decreased the content of EO units available for CO2 transport and led to a more compact structure. For Pebax1657/[Bmim][Tf2N] blend membranes, the permeabilities of N2, H2 and CH4 decreased with the increase of feed pressure due to the hydrostatic pressure effect, while CO2 permeability increased with the increase of feed pressure for that the CO2-induced plasticization effect was stronger than hydrostatic pressure effect.