(646g) Tuning Separation Properties of Carbon Molecular Sieve Membranes with Diamine Dopants

Graham B. Wenz and William J. Koros

Georgia Institute of Technology

Atlanta, GA 30332

Natural gas separations have become increasingly important as worldwide natural gas production has increased in the past decade. Common natural gas impurities, such as CO₂, must be removed in order to protect equipment and meet pipeline specifications for transmission. Carbon molecular sieve (CMS) membranes, formed by high temperature pyrolysis of polymers under controlled conditions, have emerged as a new class of materials that can surpass the polymer â??upper boundâ?. Similar to their glassy polymer precursors, CMS membranes display a physical aging phenomenon where productivity loss couples with a mild increase in selectivity when monitored over time. This behavior is thought to be cause by the relaxation of â??free volumeâ? trapped within the CMS structure during formation. This work outlines a new post-synthetic modification technique where CMS membranes are exposed to a solution containing PPM levels of amine dopants, with the original goal of preventing the â??free volumeâ? relaxation within CMS materials. While long term CO₂ and CH₄ permeation experiments showed aging-resistant membranes did not result, attractive performance resulted from the amine doped materials. The results of these experiments suggest amine doping as new technique to selectively modify the large pores present within the CMS microporous structure, resulting in increased size and shape based selectivity.