Gas separation performance of carbon dioxide-selective poly(vinyl alcohol) - ionic liquid blend membranes: The effect of temperature, feed pressure and humidity

Membrane separation technology is rapidly emerging as an alternative to traditional gas separation processes, and increasingly challenging separations require a constant search for new and better-performing materials. This paper reports the gas separation performance of a poly (vinyl alcohol) (PVA) membrane blended with 53 wt% of the ionic liquid 1-ethyl-3-methyl-imidazolium dicyanamide ([EMIM][DCA]), known from our previous work as highly CO/H "reverse-selective" material, under different experimental conditions. The material properties of the solution-cast membranes are discussed and compared with the neat PVA polymer. Pure gas permeation measurements show a drastic increase of permeability for all gases (H, He, O, N, CH, and CO) compared to the neat polymer, with a change from diffusion-selective to sorption-selective behaviour. The gas permeability further increases over the temperature range from 25 °C to 55 °C and is accompanied by a decrease in selectivity for most gas pairs, in particular, CO/N and CO/CH, except for the H/CO gas pair. Mixed gas permeation measurements with the CO/CH mixture show a beneficial effect of humidity on permeability and selectivity. This is supported by vapour sorption measurements, which show the high affinity of the membrane for water vapour and the vapour of lower alcohols.