# The calculation of thermodynamic properties and phase equilibria using a new cubic equation of state

thesis

posted on 29.11.2012, 12:33 by Navin C. PatelA new three constant equation of state for fluids and fluid
mixtures has been proposed. The equation contains three constants
and is a more general form of the Peng-Robinson equation. In
addition to the critical temperature and the critical pressure,
two parameters are required to characterize a particular fluid.
These parameters have been evaluated by minimizing the deviation
in the saturated liquid densities while simultaneously satisfying
the equilibrium criteria (equality of fugacities) along the saturation
curve. Thus, prediction of volumetric properties in the
saturation region and other regions of the phase diagram is
improved, while accuracy in the prediction of vapour-liquid
equilibrium is maintained. Parameters for hydrocarbons and nonhydrocarbons
of importance to the synthetic fuel industry are
presented. The new equation is extended to mixtures by using
mixing rules similar to those used by Peng and Robinson. Only
one binary interaction coefficient is sufficient for the accurate
prediction of vapour-liquid equilibria. Optimum values of
the binary interaction coefficients for hydrocarbon-hydrocarbon
and hydrocarbon-non-hydrocarbon systems have been obtained using
the new equation, the Peng-Robinson equation and the Soave modification
of the Redlich-Kwong equation. The criterion used for
selecting the optimum interaction coefficient is the minimization
of deviations in bubble point pressures. The new equation has been
tested for the prediction of volumetric behaviour of pure fluids
and the phase and volumetric behaviour of binary, ternary and
multicomponent systems. Comparisons with conventional equations
(P-R, S-R-K, R-K and B-W-R-S) are shown.
The applicability of van-der-Waals orie fluid model to
_ generalised equations of state is demonstrated. The equations
of Han and Starling, Simonet and-Behar and Chaudron et al have
been compared for volumetric predictions. The Han and Starling
equation has also been used with two sets of mixing rules to predict
vapour-liquid equilibrium. The van-der-Waals one fluid model has been shown to be a simple and effective method of applying the complicated
equations of state to the prediction of thermodynamic
properties of mixtures.
A generalised form of the corresponding states principle
using two non-spherical reference fluids is presented. This
represents an alternative method of extending the equation of
state approach to fluids and fluid mixtures when experimental
data are not available.

## History

## School

- Aeronautical, Automotive, Chemical and Materials Engineering

## Department

- Chemical Engineering