Adsorption and dissolution of methane at the surface of the methanol-water mixture

Abstract

Adsorption and dissolution of methane at its interface with methanol-water liquid mixture was studied by applying classical molecular dynamics simulations. The role of molecular level roughness of the liquid surface on the dissolution of methane was examined by determining the average density profile of methane along the direction perpendicular to the interface. It is revealed that a methane molecule is more likely to enter the bulk liquid through the humps of the rough liquid surface. The effect of composition of the liquid on the molecular level roughness of its surface was examined. The results indicate that with an increase in concentration of methanol in the liquid, its surface becomes more rough in terms of height and depth of the humps and wells. The larger humps at the surface of methanol rich mixture suggest an enhanced dissolution of methane into the liquid through these humps. The distribution of methane adsorbed above the liquid surface was also examined which indicated a larger methane density above the wells than the humps. The non-uniform distribution of methane is explained in terms of the potential energy of its interaction with the molecules of the liquid. The effect of methane on the orientation of interfacial methanol molecules was analyzed and it is revealed that the presence of methane enhances the tendency of these methanol molecules to have their methyl groups oriented towards the gas phase.