For the prediction of the condensation behavior of natural gas,
one has to select an equation of
state (EoS) which will be accurate in the temperature and pressure
range of interest (10 <
P/bar < 70 bar and 250 < T/K < 310).
Another requirement of the selected EoS is that it
easily
can be adapted to a characterization procedure for the heavy-end
fraction. For that purpose,
two equations were tested: the Peng−Robinson (PR), which is one of
the most applied cubic
EoS, and the simplified-perturbed-hard-chain theory (SPHCT) equation,
which is one of the
simplest EoS based on sound statistical mechanical principles. In
the underlying study, their
predictive capabilities for the prediction of saturated vapor pressures
of pure compounds and
vapor/liquid equilibrium pressures for binary mixtures are compared.
Only components present
in natural gas are considered. In addition, new pure-component
parameters for the SPHCT
EoS for n-alkanes are evaluated. Also a method to find
the characteristic energy for non-n-alkane molecules is proposed in this study. This study revealed
that the PR EoS predicts more
accurately the liquid phase composition, whereas the SPHCT EoS is
superior for the gas phase
prediction, especially for asymmetric binary mixtures. It was
concluded that, with respect to
the purpose of this study, both EoS, when used with optimum binary
interaction parameters,
have an equivalent descriptive accuracy. Therefore, the simpler PR
EoS was preferred to describe
natural gas mixtures.