Generalization of effect of oxygen exposure on formation and performance of carbon molecular sieve membranes

Previously, a pyrolysis method was developed to control separation performance of carbon molecular sieve (CMS) membranes by doping with trace oxygen. This method involved oxygen exposure during pyrolysis to tune the selective pore windows. During the development, it was observed that oxygen concentration in inert gas, rather than the total amount of oxygen exposed controls performance. In this study, we hypothesized that mass transfer of oxygen in CMS membranes during pyrolysis is governed by chemical reaction at critical pore opening. Effect of thermal soak time, inert flow rate, and precursor thickness were conducted to test this hypothesis with 6FDA/BPDA-DAM and Matrimid® polymer precursors. Results of oxygen consumption from pyrolysis process and CO2/CH4 separation performance showed that the process is likely governed by reaction kinetics. This observation implies simplicity and easy scale-up for the oxygen “doping” method on CMS formation by tuning the oxygen concentration in the pyrolysis atmosphere.