Effects of carbonisation on pore evolution and gas permeation properties of carbon membranes from Kapton® polyimide

Carbon membranes were prepared by carbonisation of Kapton® polyimide at different temperatures under vacuum and nitrogen flow. Pore structure development of the membranes during carbonisation was studied. Carbonisation temperature was critical in the modification of membrane structure. At the same temperature, the carbon membranes fabricated under nitrogen atmosphere had higher gas permeances than those fabricated under vacuum. During heat treatment, the value of d-spacing for the carbon membranes decreased with increasing temperature, however, vacuum and nitrogen atmosphere had different influences on the changes in the d-spacing. CO2 adsorption showed that the carbon membranes prepared at 1273 K under vacuum had the highest micropore volume whilst the membranes prepared at 1073 K under vacuum had the highest characteristic adsorption energy. N2 adsorption showed that the samples obtained at 873 K under vacuum had the highest nitrogen uptake. Mesopores were deemed to be connected through micropores and narrow channels between meso- and/or micropores were supposedly present. The micropores predominantly controlled the transport properties of the carbon membranes. The membrane samples obtained at 1173 K under vacuum yielded ideal separation factors of 558.27, 60.87, 19.69 and 138.53 for He/N2, CO2/N2, O2/N2 and CO2/CH4, respectively, with permeances of 7.26, 0.79, 0.26, 0.13 and 0.006 mol/(m2 s Pa) for He, CO2, O2, N2 and CH4, respectively.