Estimation of the Compressibility Factor of Nanoconfined Alkanes along Vapor–Liquid Coexistence

This study determines the effect
of surface chemistry
and the degree
of nanoconfinement on the compressibility factors of methane, n-butane, and n-octane along vapor–liquid
coexistence. This study also compares the bulk saturation compressibility
factor of the selected alkane model to the corresponding experimental
data. The saturated compressibility factors for the studied alkanes
reasonably agree with the corresponding experimental data, with the
maximum deviation shown by n-octane saturated vapor
being less than 19%. The maximum change in the reduced compressibility
factor of nanoconfined saturated liquid alkanes and saturated vapor
alkanes to the corresponding bulk values is around 72 and 105%, respectively,
for the studied slit pore in quasi-3D to quasi-2D regions. Interestingly,
in ultrananopores (quasi-2D), the nanoconfined alkanes have shown
an insignificant effect of the confining surface chemistry on the
reduced compressibility factor of coexistence-saturated fluids. The
critical compressibility factor of alkanes for the studied nanoconfinement
has shown a nonmonotonic trend with the inverse of the nanopore width.
Moreover, with a larger nanopore width, the critical compressibility
factor approaches the corresponding bulk value.