Permeation and sorption properties of CO2-selective blend membranes based on polyvinyl alcohol (PVA) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) ionic liquid for effective CO2/H2 separation

This paper reports on the preparation and testing of blend membranes based on polyvinyl alcohol (PVA) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) ionic liquid (IL) for effective CO/H gas separation. Stable membranes with 9, 14, 24, 42 and 53 wt.% of IL were prepared via the solution casting procedure. Structural analysis (XRD, Raman, TGA and DSC) revealed that the increase of the incorporated IL content in PVA affected e.g. crystalline orientation in the diffraction plane 1 0 1 in favour of plane 2 0 0. The presence of the IL shifted the Tg (65 °C) and Tm (165 °C) of neat PVA to lower temperatures, towards the values of pure IL. The gas transport in neat PVA and PVA-IL blends with low IL content was found to be diffusivity-controlled, and the IL addition leads to an increase of both gas permeability and H/CO selectivity. Instead, membranes with an IL content above 20 wt.% were more permeable for CO due to the prevailing solubility-controlled mechanism. Compared to neat PVA, which has barrier properties, the sample PVA-IL with 53 wt.% of IL exhibited an exceptional increase in gas permeability for both gases, H circa 150 times to 8.65 Barrer and CO permeability circa 2400 times to 66.9 Barrer, with the corresponding ideal CO/H selectivity of 7.73 that slightly exceeds the reverse CO/H Robeson 2008 upper bound.