posted on 2021-06-14, 20:43authored byReihaneh Toutouni, Jan Kubelka, Mohammad Piri
Molecular dynamics (MD) simulations
were used to study vapor–liquid
equilibrium interfacial properties of n-alkane and n-alkane/CO2 mixtures over a wide range of pressure
and temperature conditions. The simulation methodology, based on CHARMM
molecular mechanics force field with long-range Lennard-Jones potentials,
was first validated against experimental interfacial tension (IFT)
data for two pure n-alkanes (n-pentane
and n-heptane). Subsequently, liquid–vapor
equilibria of CO2/n-pentane, propane/n-pentane, and propane/n-hexane mixtures
were investigated at temperatures from 296 to 403 K and pressures
from 0.2 to 6 MPa. The IFT, liquid and vapor phase densities, and
molecular compositions of the liquid and vapor phases and of the interface
were analyzed. The calculated mixture IFTs were in excellent agreement
with experiments. Likewise, calculated phase densities closely matched
values obtained from the equation of state (EOS) fitted to the experimental
data. Examination of the density profiles, particularly in the liquid–vapor
transition regions, provided a molecular-level rationalization for
the observed trends in the IFT as a function of both molecular composition
and temperature. Finally, two variants of the empirical parachor model
commonly used for predicting the IFT, the Weinaug–Katz and
Hugill–Van Welsenes equations, were tested for their accuracy
in reproducing the MD simulation results. The IFT prediction accuracies
of both equations were nearly identical, implying that the simpler
Weinaug–Katz model is sufficient to describe the IFT of the
studied systems.