Molecular dynamics study of pervaporation of water-methanol mixtures through graphene nanotubes.

By means of extensive molecular dynamics simulations, we explore the concentration enhancement of alcohol from water/methanol solutions induced by the preferential flow of alcohols through single-layer carbon nanotubes of various widths. These nanotubes connect a reservoir containing an aqueous methanol solution with an empty reservoir. Simulations are performed at room temperature and at 398 K. The non-equilibrium stages of these simulations can represent a rough model of the pervaporation process through a hydrophobic membrane channel. Once equilibrium is reached in the receiving reservoir, we observe a substantial increase in alcohol concentration with respect to the value that would correspond to the gas phase in an unconfined vapor-liquid equilibrium at the same temperature. Alcohol yields are particularly high when starting from dilute alcohol solutions and for nanotubes 2-3 times wider than the average adsorbate molecular size.