(509a) Using SAFT-FMT-DFT to Model the Adsorption of Light Gases and Hydrocarbons in Activated Carbon

The use of molecular simulation, the development of accurate models, and the comparison of theoretical predictions with experimental results help to advance our understanding of adsorption and its application.  One prominent molecular model is density functional theory (DFT), which is commonly used to treat the adsorption of spherical molecules in slit-shaped carbon pores.  In this paper, we couple DFT with an accurate molecular-based equation of state to calculate the fluid thermodynamic properties using fundamental measure theory (FMT), which is a rigorous theory for homogeneous and non-homogeneous hard-sphere chain fluids. An accurate model is obtained with adsorbing molecules treated as hard-sphere chains with square well interactions.  The Mansoori-Carnahan-Starling-Leland and Carnahan-Starling-Boublik equations of state are used for the hard sphere interactions, and the statistical associating fluid theory for potentials of variable range (SAFT-VR) is used to describe the square-well fluid.  For adsorption in pores, various potentials can be used for the interaction of the chain molecules with the wall.  After comparing model predictions with results from Monte Carlo simulations, the model is used to obtain a pore size distribution for activated carbon from experimental data for adsorption of nitrogen, which is treated as a non-spherical molecule.  The adsorption of n-pentane in slit-shaped carbon pores of various widths is then predicted from the model, and together with the pore size distribution, adsorption isotherms are obtained for comparison with experimental data.