A novel
method to evaluate volumetric properties, namely the thermal
expansivity (α
P
) and the isothermal
compressibility (κ
T
) for nonpolar
hydrocarbon systems using refractive index measurements, is presented
in this work. New expressions for α
P
and κ
T
are derived from the Lorentz–Lorenz
equation and the One-Third rule, respectively. A further simplified
expression for α
P
is proposed requiring
only refractive index data and molecular weight for calculation. Densities
and refractive indices of 12 pure nonpolar hydrocarbons, 6 hydrocarbon
mixtures, and 3 crude oils are measured at temperatures from 283.15
K up to 343.15 K and at 0.1 MPa. The measured refractive indices are
used to calculate α
P
for a wide
range of temperatures using the proposed method, and the measured
densities are used to calculate α
P
for comparison. Reported densities and refractive indices of benzene
at 298.15 K and at pressures up to 90 MPa are used for κ
T
evaluations with the proposed method. Values
of α
P
and κ
T
calculated from refractive index measurements are in good
agreement with experimental data and those determined from densities.
This work aims to establish the foundation for experimental methods
to determine volumetric properties of nonpolar hydrocarbon systems
based on refractive index measurements. A high temperature and high
pressure refractometer is expected to have multiple advantages over
conventional techniques for density measurements, which include but
are not limited to smaller amounts of sample needed, simpler calibration,
faster measurement, and cells that are corrosion-resistant (i.e.,
sapphire glass).
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