A methodology for the morphological and physicochemical characterisation of asymmetric carbon hollow fiber membranes

Carbon and activated carbon hollow fiber membranes were prepared from an asymmetric co-polyimide precursor through the application of common pyrolytic carbonization procedures followed by carbon dioxide activation. A complete analytical methodology, consisting of a combination of advanced static and dynamic techniques, is proposed as a tool to elucidate the asymmetric pore structure of the developed carbon membranes. More specific, the carbon hollow fiber morphology was investigated by scanning electron microscopy. The mean micropore size of the existing separating layers was defined by surface excess adsorption of the probe molecules H2, CO2, N2 and CH4. The micropore size distribution was derived by means of the Grand Canonical Monte Carlo simulation method, using the experimental data of either the H2 77 K or both H2 and CO2 adsorption isotherms. In addition, single phase and relative permeability experiments revealed the coexistence of a small population of mesopores on the pore structure of the dense separating layers. Overall, the proposed methodology has been proved sufficient to distinguish the simultaneous occurrence of three separating layers in each of the developed membranes and discriminate between their different pore structures.