(551c) Suppression and Reversal of Physical Aging in Carbon Molecular Sieve Hollow Fiber Membranes

Carbon molecular sieve (CMS) materials can provide high performing membranes for many challenging gas pair separations. By pyrolyzing polymer precursors under an inert atmosphere, ultramicroporous sheets are formed. These sheets stack imperfectly, thereby producing micropores between the sheets that control diffusion jump lengths and sorption. The constituent sheets transition to a closer packing state to reach a more thermodynamically stable state. The closer packing leads to lower permeability and is referred to as physical aging. Our group has discovered that physical aging in CMS can be suppressed by storage under moderate (100 psig) carbon dioxide. After a physical aging process occurs in a simple amorphous polymer glass, rejuvenation can be achieved via temperature cycle or sorption cycle processes. CMS materials are complex glasses due to their sheet like nanostructures, and it has been thought previously that CMS rejuvenation would be impossible due to irreversible reduction in micropore volumes. In this presentation, we will provide data and analysis to explain the CMS permeability loss and subsequent rejuvenation in terms of rearrangement within the ultramicropore distribution.