(396aa) New Insights On Carbon Dioxide and Methane Transport in Carbon Molecular Sieve Membranes From Diffusion NMR Studies

Carbon molecular sieve (CMS) membranes are promising materials for energy-efficient separations of light gases of particular interest in energy applications. This work focuses on the separation of mixtures containing carbon dioxide and methane which are ubiquitous in natural gas and bio-gas streams. Here we present and discuss selected results of microscopic studies of self-diffusion of carbon dioxide and methane in samples of CMS membranes optimized for methane/carbon dioxide separations. These diffusion data were obtained by a pulsed field gradient (PFG) NMR method that combines advantages of using large (up to 30 T/m) magnetic field gradients and high (17.6 T) magnetic field. An application of large field gradients allows measuring relatively small diffusivities of gases in CMS membranes, while high field was essential for obtaining sufficiently large signal-to-noise ratios in diffusion studies.   The microscopic diffusion data obtained by PFG NMR will be discussed in relation to previous macroscopic observations of membrane selectivities and permeabilities measured for the same gases in the same membranes.