Carbon membranes from blends of PBI and polyimides for N2/CH4 and CO2/CH4 separation and hydrogen purification

Membranes composed of poly(benzimidazole) (PBI) and various polyimides are studied regarding to their capabilities in formation of homogenous blends with satisfactory morphology for fabrication of gas separating carbon molecular sieve membranes. Attempts are made to unravel the correlations between the pyrolysis process parameters and separation performance of developed membranes. The results show that compared to Torlon and P84, Matrimid is a better choice for preparation of blend precursors in combination with PBI. The findings also suggest that carbon membranes derived form PBI/Matrimid are congruous candidates for H-2/CO2 separation. Interestingly, attractive performance for separation of other gas pairs were obtained by tuning the PBI content in membranes. Modification of precursors by chemical cross-linking prior to carbonization provides membranes with enhanced selectivity suitable for separation of hydrogen from both nitrogen and carbon dioxide. This research study accentuates the necessity and importance of adopting a proper strategy in exploiting synergistic beneficial features of advanced materials (PBI), technology (polymer blending), process (carbonization) and modification techniques (cross-linking) toward achieving membranes with desired performance. Developed membranes surpass several separation performance trade-offs with great potentials for various industrial applications including CO2/CH4 (alpha = 203.95), H-2/CO2 (alpha = 33.44) and particularly N-2/CH4 separation with unprecedented high permeability (P-N2 = 2.78 Barret) and selectivity (alpha = 7.99) for this gas pair. (c) 2008 Elsevier B.V. All rights reserved.