Bulk and Interfacial Properties of the Alkane + Nitrogen System

Molecular dynamics simulations were performed to investigate
the
bulk and interfacial properties of the alkane + N2 system
at geological conditions. n-C10 + N2, n-C16 + N2, and branched C16 + N2 systems
are mainly considered in this study. The simulation results were compared
to theoretical modeling using the VT-PPR78 equation of state and the
density gradient theory, and the results are in good agreement with
the experimental findings. The density profiles of alkanes varied
monotonically across the interfaces, but N2 molecules are
found to enrich the interfaces. The solubility of N2 in
the alkane-rich phase increases with temperature, likely due to entropic
factors. This solubility also increases with pressure, likely due
to energetic factors. There was no significant effect of the alkane
size Nm and the chain
branching on the solubilities of N2 in the alkane-rich
phase. We observed a direct correlation between the solubility of
N2 in the alkane-rich phase and the swelling of the alkane-rich
phase. The interfacial tension (IFT) of the alkane + N2 system decreases with pressure, and this decrease is less marked
at higher temperatures. For this system, the IFT decreases with temperature.
Also, these IFTs increase with Nm and decrease with chain branching. Furthermore, the surface
excess of N2 changes nonmonotonically as a function of
pressure in the alkane + N2 system. The fact that the IFTs
decreased with pressure might be explained by the positive surface
excess of N2. The surface excess of N2 decreases
with temperature. This explains why the decrease in the IFTs with
pressure is less marked at higher temperatures. There was no significant
effect of Nm and chain
branching on the surface excess of N2.