Poly（amide-6-b-ethylene oxide）/BmimTf2N blend membranes for carbon dioxide separation

摘要

Poly(amide-6-b-ethylene oxide)(Pebax1657)/1-butyl-3-methylimidazo-lium bis[trifluoromethyl)sulfonyl]-imide([Bmim][Tf_2N]) blend membranes with different [Bmim][Tf_2N] contents were prepared via solution casting and solvent evaporation method. The permeation properties of the blend membranes for CO_2, N_2,CH_4 and H_2 were studied, and the physical properties were characterized by differential scanning calorimeter(DSC) and X-ray diffraction(XRD). Results showed that [Bmim][Tf_2N] was dispersed as amorphous phase in the blend membranes, which caused the decrease of Tg(PE) and crystallinity(PA). With the addition of [Bmim][Tf_2N], the CO_2 permeability increased and reached up to approximately 286 Barrer at 40 wt%[Bmim][Tf_2N], which was nearly double that of pristine Pebax1657 membrane. The increase of CO_2 permeability may be attributed to high intrinsic permeability of [Bmim][Tf_2N], the increase of fractional free of volume(FFV) and plasticization effect. However, the CO_2 permeability reduced firstly when the [Bmim][Tf_2N]content was below 10 wt%, which may be due to that the small ions of [Bmim][Tf_2N] in the gap of polymer chain inhibited the flexibility of polymer chain; the interaction between Pebax1657 and [Bmim][Tf_2N]decreased the content of EO units available for CO_2 transport and led to a more compact structure. For Pebax1657/[Bmim][Tf_2N] blend membranes, the permeabilities of N_2, H2 and CH4decreased with the increase of feed pressure due to the hydrostatic pressure effect, while CO_2 permeability increased with the increase of feed pressure for that the CO_2-induced plasticization effect was stronger than hydrostatic pressure effect.