(193a) Development and Application of the SAFT-FMT-DFT Approach for Adsorption Equilibrium

LeVan, M. D., Vanderbilt University
Schindler, B. J., Vanderbilt University
Mitchell, L. A., Vanderbilt University
McCabe, C., Vanderbilt University

Density functional theory (DFT) is commonly used to treat the adsorption of molecules in carbon and silica pores of various geometries.  We have developed a DFT with an accurate molecular-based equation of state to calculate thermodynamic properties using fundamental measure theory (FMT), which is a rigorous approach for the treatment of homogeneous and non-homogeneous hard-sphere fluids.  A theoretical framework results with adsorbing molecules treated as hard-sphere chains with square-well attractive interactions.  The Mansoori-Carnahan-Starling-Leland and Carnahan-Starling-Boublik equations of state are used for the hard sphere interactions, and a version of the statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to describe the square-well fluid.  First and second order perturbative attractive terms are included in the theory.  The theoretical predictions are in good agreement with published results for Monte Carlo simulations of the adsorption of chain molecules. 

In this talk, the SAFT-FMT-DFT approach is used to develop a pore size distribution for BPL activated carbon based on nitrogen adsorption, and that pore size distribution is used to predict the adsorption of n-pentane on the activated carbon.  Interaction parameters are obtained by simulating data for adsorption of nitrogen and n-pentane on the planar wall of a non-porous graphitized carbon.  The 10-4-3 fluid-wall potential is used to model adsorption in the slit-shaped pores of the activated carbon.  The single pore nitrogen isotherms simulated with the DFT theory show monolayer transitions, pore filling, and pore condensation.  The predicted excess n-pentane isotherm is compared with a unique experimental n-pentane isotherm that extends into the Henry's law region.  The predicted isotherm agrees well with the experimental results.