Development and characterization of micropores in carbon molecular sieve membrane for gas separation

Defect-free carbon molecular sieve membranes were formed by pyrolysis of a polyimide precursor. The micropore structures of the carbon molecular sieve membranes were studied for different pyrolysis temperatures and atmospheres. From attenuated total reflectance Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and density measurements on these materials, it appears that pyrolysis under vacuum and at high temperature increases the degree of carbonization and creates smaller micropores. Differential thermoanalysis and thermogravimetry coupled to mass spectroscopy were performed to understand the thermal stability and pyrolysis phenomena. The results indicated that, between 400 and 600 degrees C, large micropores were created by the release of large-molecule volatile fragments and then, between 460 and 1000 degrees C, ultramicropores formed due to liberation of small-molecule volatile products. Microporosity of the carbon molecular sieve membranes was studied using gas permeation, transmission electron microscope, positron annihilation lifetime spectroscopy, and analysis of argon adsorption isotherms via density functional theory. It was found that pyrolysis under vacuum and at high temperature produced large numbers of ultramicropores within a narrow pore-size distribution. The permeability and solubility data showed a strong dependence on microporosity. (C) 2011 Elsevier Inc. All rights reserved.