Surface Tension and Adsorption at the Vapor–Liquid Interface in a Methane–Ethane System

Russian Journal of Physical Chemistry A. 2024. Vol. 98. No. 12. P. 2816–2822.

Lenev D. Y., Zakharov S. A., V. V. Pisarev

Molecular dynamics is used to calculate the vapor–liquid equilibrium and liquid–vapor surface
tension for a methane–ethane system. Good agreement of the parachor value for ethane between the molecular
model and experimental data is shown for the 203–253 K range of temperatures and pressures up to
60 atm. The dependence of the surface tension of the mixture on pressure in the range of 4–40 atm at a temperature
of 213 K shows a drop in both the surface tension and the difference in densities between the liquid
and vapor as the pressure rises and approaches the critical locus. Approximating the density profiles obtained
for the same conditions, it is concluded that the width of the interphase boundary also grows. The amount of
methane adsorbed on the surface of the liquid film is calculated. The dependence of the molar adsorption of
methane on the difference between the densities of the components in the liquid and gas phases is obtained,
along with its analytical expression in the context of the Gibbs theory. Features of the approach that is used
include no need for approximations of the ideal gas or the ideal solution, and the use of only experimentally
obtained data as input. The resulting values of methane adsorption are in good agreement with the derived
analytical dependence.

Keywords: molecular dynamics, adsorption, interface tension