Fabrication and characterization of polyetherimide Supported Ionic Liquid Membranes for gas separation

In the last decades, many studies have been addressed on the application of membrane technology in the field of gas separation. The most widespread membranes for gas separation are polymeric membranes, but several other configurations have been studied, among which heterogeneous membranes made by a polymeric support and a selective liquid, namely Supported Liquid Membranes (SLMs). Among the liquids used in this application, ionic liquids (ILs) display promising features, linked to their high viscosity, thermal stability and good affinity with CO2. For this reason, Supported Ionic Liquid Membranes (SILMs) have been widely investigated, in particular in their potentiality in CO2 removal. The aim of this work is to study the applicability of polyetherimide (PEI) as supports for SILMs for gas separation. For this purpose, PEI porous matrix from different polymer solutions and different fabrication techniques are prepared. In particular, two phase inversion (PI) techniques have been investigated: the non-solvent induced PI and the Evaporation Induced PI. While the PEI matrixes prepared by NIPS technique present porosity of sizes of 3-5 μm suitable for the immobilization of a liquid phase, only dense structures have been obtained by solvent evaporation. Porous PEI supports are impregnated with an organic solvent (PEG 400) and an ionic liquid [bmim][BF4], leading to SLMs and SILMs, respectively. The permeability of N2, CO2, CH4, O2 and air is measured and the ideal selectivity of four gas pairs is calculated. All membranes display separation performances which are lower than those expected by the selective liquids and that are below the state-of-the art of membrane technology for gas separation. An analysis on the permeability of the two phases (polymer and liquid), aided by Maxwell-Wagner-Sillar theory for permeability in a heterogeneous medium, has revealed a simple but effective method to differentiate among different porous structures for SLMs and SILMs.