Selective removal of butanol from aqueous solution by pervaporation with a PIM-1 membrane and membrane aging

In this work, the selective removal of butanol from aqueous solution by pervaporation with a polymer of intrinsic microporosity (PIM-1) membrane was studied. The freshly cast and aged (370 days) PIM-1 membrane was used for pervaporation experiments at 50 °C. The aged PIM-1 membrane exhibited a decrease of permeability coefficient compared to the freshly cast membrane, from 9.0 × 10−5 to 1.1 × 10−5 mol m−1 kPa−1 h−1 for 1-butanol and from 3.2 × 10−5 to 2.2 × 10−6 mol m−1 kPa−1 h−1 for water, but simultaneously an increase of selectivity, from 2.8 to 5.1, for the separation process at 2 wt.% of butanol. The aging effect may be attributed to slow rearrangement of polymer chains, resulting in densification and reduction of accessible free volume. Renewed soaking of an aged membrane with methanol does not restore the original permeability. The selectivity of 1-butanol increases with higher 1-butanol concentration for fresh PIM membrane, however the opposite trend was observed for aged PIM-1 membrane.