In situ regulation of micro-pore to design high performance polyimide membranes for pervaporation dehydration of isopropanol

By employing an ionic thermally labile compound, iron(III) acetylacetonate (FeAc), coupled with high temperature annealing on cross-linkable polyimide materials, we have designed a novel strategy for in situ micro-pore formation with a regulated size and distribution in membranes. The micro-pores were formed by acetylacetonate decomposition and decarboxylation, while their pore size was regulated by ionic and thermal induced cross-linking. In addition, the free standing iron(III) ions releasing from decarboxylation formed iron oxide nano-particles that also enhanced water sorption of the nano-composite membranes. All membranes have acceptable mechanical strength and flexibility. The effects of FeAc loading and annealing temperature on pervaporation performance towards IPA/ water dehydration were studied. The newly designed dense membrane with 20wt% FeAc followed by a thermal treatment at 400°C exhibited the best performance with a permeability of 0.467mgm^-1h^-1KPa^-1 and a water/IPA molar selectivity of 4746. Compared to the pristine polyimide, the molar selectivity of the new membrane was improved by more than 100 times. Results from positron annihilation lifetime spectroscopy (PALS) also confirmed that the newly developed membranes have a bimodal pore size distribution with improved sieve capability.