Using iron (III) acetylacetonate as both a cross-linker and micropore former to develop polyimide membranes with enhanced gas separation performance

Abstract

Cross-linking polymer chains has proved to be one of the feasible ways to improve its gas separation performance and plasticization resistance, but often at the expense of permeability. In this study, an attempt to cross-link a polyimide (PI) without sacrificing the permeability of the membrane is made by employing an ionic thermally labile unit, iron (III) acetylacetonate (FeAc), coupled with low temperature annealing. Particularly, not only a cross-linked network is established, an increment of more than 88% in permeability is attained for the PI–6wt% FeAc membrane as compared to pristine PI membrane. The permeability enhancement is resulted from increments in both solubility and diffusivity coefficients. The modified membranes also show improved resistance to CO2 plasticization in both pure CO2 and binary CO2/CH4 gas tests. Various characterization techniques such as TGA, DSC, FTIR, gel content and density measurement were employed to elucidate the structural changes of the PI–FeAc membranes during the cross-linking and annealing processes. A moderate post thermally treated polyimide membranes blended with iron (III) acetylacetonate with enhanced gas separation performance, improved CO2 plasticization resistance and good stability under mixed gas has been developed.