Engineering of Physical Aging to Optimize Carbon Molecular Sieve (CMS) Hollow Fiber Membranes

Carbon Molecular Sieve (CMS) hollow fiber membranes can transcend the permeability/selectivity upper bound for many important gas pair separations such as CO₂ vs CH₄ and C₃H₆ vs C₃H₈ [1 – 2]. Such membranes are made by pyrolyzing polymeric precursors under inert atmospheres to form amorphously distributed carbon sheets. The amorphous CMS material has micropores between sheets and includes ultramicropores within the sheets themselves. There is a driving force for the carbon sheets to arrange themselves into more thermodynamically stable, denser packing states with fewer and smaller micropores. This rearrangement causes a reduction in the penetrant diffusion jump lengths and sorption capacities, thereby reducing permeance. These complex changes are henceforth referred to as physical aging. Physical aging can potentially limit the utility of CMS membranes. Fortunately, physical aging can be minimized by introducing condensable sorbent molecules in the CMS micropores. These temporary molecular pillars still allow structural rearrangement of the micropores to reflect the size of the sorbed molecules. Ideally, removing the sorbent molecules via a purging technique before placing in service provides the CMS with sustained attractive performance. In this poster, hollow fiber properties and several engineered storage techniques of CMS will be discussed, along with the fundamental factors associated with each.

1. Mayumi Kiyono. Carbon Molecular Sieve Membranes for Natural Gas Separations. Ph.D., Georgia Institute of Technology, Atlanta, GA, December 2010.
2. Liren Xu. Carbon Molecular Sieve Hollow Fiber Membranes for Olefin/Paraffin Separations. Ph.D., Georgia Institute of Technology, Atlanta, GA, December 2012.