(727f) Capture and Separation of CO2 From Binary Gas Mixtures Using Flexible Porous Coordination Polymers

Structurally dynamic coordination polymers or metal organic frameworks (MOFs) are a unique class of CO₂ sorbents that undergo structural phase transitions from low porosity “closed pore” structures to high porosity “open pore” structures once a critical threshold pressure of CO₂ is reached.  The adsorption isotherms for these compounds show a pronounced step at the threshold pressure followed by a large increase in CO₂ uptake.  Subsequent desorption of CO₂ from the saturated state is highly hysteretic.  The threshold pressure and the width of the hysteresis loop in these compounds are not only functions of temperature and material structure, but also highly dependent on the identity of the adsorbate.  As such, they are of intense interest for their potential as gas selective sorbents.  One important fundamental question surrounding these structurally dynamic materials is whether the selectivity suggested by the pure gas isotherms is preserved in the presence of gas mixtures, or does the adsorption of one gas open the structure and allow other gases access to the newly created pore structure. Understanding the adsorption mechanisms in these materials under mixed gas conditions is therefore critical for evaluating their separation abilities and limitations.  To address this question, a series of structurally dynamic porous coordination polymers have been evaluated for CO₂ capture from mixed gas streams using a variety of experimental techniques including in situ infrared spectroscopy, small angle neutron scattering, gas chromatography and high pressure breakthrough curves.