Poly(ionic liquid) augmented membranes for π electron induced separation/fractionation of aromatics

Abstract

Novel polyionic liquid augmented membranes were fabricated using pressure assisted self-assembly and employed for π- electron cloud mediated separation of aromatics from their aliphatic homologues, which are otherwise difficult to achieve by conventional size exclusion basedmembrane filtration. The electron withdrawing/electron donating substituents on aromatic ring, which can lead to an overall change in the π cloud density on aromatic ring, can be employed in fractionating such aromatics such as benzene, toluene, p-xylene, nitrobenzene. High π electron could density due to extended conjugation over more than one aromatic ring was also utilized in fractionation of benzene, naphthalene, anthracene and phenanthrene. The most interestingly, these PIL augmented membranes were demonstrated to have preferential separation of one stereoisomer over other. The preferential separation of trans-stilbene over cis-stilbene was attributed to stereo-chemical arrangement assisted deviating from planarity of aromatic moieties of the later resulting deterioration of overall extended conjugation and π electron cloud delocalization. These PIL membranes also exhibited the preferential separation of regioisomers of bipyridine. These PIL augmented membranes were found to stable in presence of mainly non-polar organic diluents due to the π- stacking interaction between the aromatic phenylic moieties of the polyimide support and aromatic pyridinium moieties of the poly (ionic liquid) polymers.