Evaluation of the interaction potentials for methane adsorption on graphite and in graphitic slit pores

Abstract

This paper compares the performance of the Buckingham Exponential-6 and Lennard-Jones potential models in the description of bulk phase and adsorption properties of methane on graphitic surfaces and pores. The solid-fluid potential used in the choice of the LJ model is Steele 10-4-3 equation and for the Exp-6 model, the Crowell and Chang equation which has been rarely used in the literature. From an extensive computer study using Grand Canonical Monte Carlo simulation, the two potential models perform almost equally well in the bulk fluid behavior except at extremely high density, where the LJ model is better. For adsorption on surface, the Exp-6 performs better in the correct description of the experimental Henry constant. However, both potential models describe well the isotherm outside the Henry law region. Under supercritical conditions, the same behavior is seen in the Henry law region, but the opposite is observed at extremely high pressures. For adsorption in slit pores, significant difference is seen at low pressure region for all pore sizes examined. In this region, the Exp-6 always predicts a higher capacity than the LJ model. In the smallest pore size examined (0.65 nm), the LJ model predicts a higher capacity than the Exp-6 with approximately 4% difference at higher pressures. However, this behavior is not seen in the other pore sizes. The comparison shows that the Exp-6 can describe experimental adsorption data, albeit only, better than the LJ.