Characterization of highly selective microporous carbon hollow fiber membranes prepared from a commercial co-polyimide precursor

In this work, the preparation of gas separating carbon hollow fiber membranes based on a 3,3'4,4'- benzophenone tetracarboxylic dianhydride and 80% methylphenylene-diamine + 20% methylene diamine co-polyimide precursor (BTDA-TDI/MDI, P84 Lenzing GmbH), their permselectivity properties as well as details of the carbon nanostructure are reported. Hollow fibers were initially prepared by the dry/wet phase inversion process in a spinning set-up, while the spinning dope consisted of P84 as polymer and NMP as solvent. The developed polymer hollow fibers were further carbonized in nitrogen at temperatures up to 1173 K. Thermogravimetric analysis was used to investigate the weight loss during the carbonization process. The nitrogen, methane and carbon dioxide adsorption capacity of the prepared materials was determined gravimetrically at 273 and 298 K and hydrogen adsorption experiments were performed at 77 K up to 1 bar. Scanning electron microscopy was used to elucidate the morphological characteristics and the nanostructure while H(2) sorption at 77 K was applied to evaluate the microporosity of the developed carbon hollow fiber membranes. In all cases, the permeability (Barrer) of He, H(2), CH(4), CO(2), O(2) and N(2) were measured at atmospheric pressure and temperatures 313, 333 and 373 K and were found higher than those of the precursor. Moreover, the calculated permselectivity values were significantly improved. The developed carbon fibers exhibit rather low H(2) permeance values (8.2 GPU or 2.74 x 10-9mol/m2 center dot s center dot Pa) with a highest H(2)/CH(4) selectivity coefficient of 843 at 373 K.