New polyimide-polyaniline hollow fibers: Synthesis, characterization and behavior in gas separation

New polyimide-polyaniline hollow fibers were produced by dissolution of the polymers in NMP and dry/wet spinning of the resulting solution in a non-solvent (H₂O). The morphology and thermal properties of the fibers, were examined by means of SEM and TGA, and FTIR spectroscopy was used for the study of their chemical structure. Permeability and selectivity measurements in different gases (He, H₂, CH₄, CO₂, O₂ and N₂) were performed in order to evaluate the performance of the membrane in gas separation applications. The results indicate that the novel membrane is a well structured hollow fiber, thermally stable up to 500°. The introduction of polyaniline into the polyimide matrix, results in a great enhancement in fiber permeability (60-600 times) possibly due to increase of the total free volume due to the introduction of shorter polyaniline molecules in the matrix, allowing larger quantities of gases to pass through the composite membrane. Perm-selectivity ratios for the composite membranes H₂/CH₄, He/N₂, H₂/N₂ and H₂/CO₂ were found lower by a factor of 6.4, 8.9, 7.7 and 1.47, respectively, compared to membranes produced using only polyimide. The opposite effect was observed for CH₄/CO₂ and N₂/CO₂ perm-selectivity ratios that showed an increase by a factor of 3.52 and 5.2, respectively. The ratio CH₄/CO₂ is of particular interest for natural gas purification purposes.