Properties of adsorbed supercritical methane film in nanopores

Abstract

Adsorbed natural gas technology is an efficient technology for storing natural gas at low pressure and room temperature. This work investigates the properties of the adsorbed methane film in nanopores where methane is adsorbed by strong van der Waals forces in pores of few molecular diameter as a high-density fluid. BET surface area, porosity, and pore size distribution were measured using sub-critical nitrogen adsorption. The adsorbed film thickness, the film density, specific surface area, and methane average binding energy were extracted from a single supercritical methane adsorption isotherm using Langmuir and Ono-Kondo models. In addition, this method does not require a conversion between gravimetric excess adsorption and absolute adsorption. The adsorbed film thickness is between 4.2 and 4.4 Å and the density of the adsorbed film at maximum capacity is between 302 and 340 g/L. Specific surface areas obtained from supercritical isotherms are consistent with BET surface areas from subcritical nitrogen adsorption. The binding energies obtained from the two models are compared to the ones obtained from Clausius-Clapeyron method.