Pure Appl. Chem., 2003, Vol. 75, No. 7, pp. 875-888
http://dx.doi.org/10.1351/pac200375070875
Potential of group contribution methods for the prediction of phase equilibria and excess properties of complex mixtures
Abstract:
Reliable knowledge of the thermophysical properties
of pure compounds and their mixtures in the whole composition and a
wide temperature and pressure range is a vital prerequisite for computer-aided
synthesis, design, and optimization of chemical processes. Knowledge
of the various phase equilibria is most important for the development
of thermal separation processes (but also for other applications,such
as the design of multiphase reactors, the prediction of the fate of
a chemical in the environment,etc.).
Whereas 25 years ago, the main interest was directed to the development
of predictive tools for vapor–liquid equilibria of subcritical
compounds of similar size (ASOG, UNIFAC), 15 years later a proper description
of the temperature dependence (excess enthalpies), the activity coefficients
at infinite dilution, and solid–liquid equilibria of eutectic mixtures
(including strong asymmetric systems) was achieved. After the combination
with cubic equations of state [Soave–Redlich–Kwong (SRK),
Peng–Robinson (PR)], the group contribution concept was extended
to supercritical compounds [predictive SRK (PSRK)]. With the development
of an adequate electrolyte model (LIFAC), the equation-of-state approach
can even be used for systems with strong electrolytes. With the revision
of the group interaction parameters, the extension of the parameter
matrix (introduction of new structural groups, filling of parameter
gaps), and the help of a large database (Dortmund Data Bank), the predicted
results of group contribution methods were significantly improved and
the range of applicability greatly extended. Furthermore, still-existing
problems with the group contribution approach (proximity effects,etc.)
were reduced.
With the help of a volume-translated PR equation of state and application
of temperature-dependent and improved mixing rules, the remaining weaknesses
of group contribution equations of state (such as poor results for liquid
densities, excess enthalpies, and the problems with asymmetric systems)
were minimized.