(148b) Net Adsorption Thermodynamic Framework for Microporous Solids

The net adsorption thermodynamic framework was recently introduced as an alternative to excess and absolute adsorption (Gumma and Talu, Langmuir 2010, 26(22), 17013-17023).  It is a fundamentally different thermodynamic description of adsorption since the placement of Gibbs dividing surface, necessary for any treatment of adsorption, is different than the known/used alternatives.  Net adsorption is a natural choice for microporous solids.  It removes any ambiguity in theoretical treatment of adsorption and circumvents all questionable measurements/quantities in experiments.

 Initial development of net adsorption was prompted by the interest in adsorptive gas storage and by the need to unambiguously compare experiments to molecular simulation results.  Previously, our research group and others have shown that: 1) non-adsorbing helium assumption commonly used to place the Gibbs dividing surface in experiments does not hold (e.g. Gumma and Talu, Adsorption J. 2003, 9, 17-28), 2) molecular simulation results can only be compared to excess data by performing more simulations with helium (e.g. Talu and Myers, AIChE J. 2001, 47(5), 1160-1168), and 3) volume occupied and thermal mass of solid adsorbent play a significant role in equilibrium and dynamics of adsorptive storage systems (e.g. Chang and Talu, Applied Thermal Engineering 1996, 16(5), 359-374).  As such, our previous work has concentrated on pure component adsorption equilibrium and dynamics.

 This contribution involves extension of net adsorption framework to gas mixtures.  Theoretical developments on equilibrium formulations will be included as well as its implications on adsorption processes such as column dynamics in separations and in storage.  The theory will be supplement with data examples and implementation methods.  The advantages/disadvantages and limitations of net adsorption will be discussed.