Capabilities and Limitations
of an Association Theory
for Chemicals in Liquid or Supercritical Solvents
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Abstract
The cubic-plus-association (CPA) model is an equation
of state
(EoS) that combines the Soave–Redlich–Kwong (SRK) equation
with the association term from Wertheim’s theory as used in
statistical associating fluid theory (SAFT). In the form used here,
the CPA EoS does not include separate terms for the polar and quadrupolar
contributions. The capabilities and limitations of the CPA model when
it is applied to mixtures with nonpolar and polar chemicals, as well
as associating (hydrogen-bonding) compounds are illustrated. Three
case studies are considered, all of which are of industrial relevance.
The capabilities of the model are illustrated in the first two case
studies: the phase behavior of mixtures used in the oxidation of 2-octanol
in supercritical CO<sub>2</sub> and the investigation of systems containing
acetone, methanol, water, chloroform, and methyl acetate. In each
case, both correlations of vapor–liquid and liquid–liquid
equilibria for binary systems and predictions for multicomponent mixtures
are presented. Finally, the limitations of the CPA model are illustrated
in the last case study, which focuses on the modeling of mixtures
containing aromatic acids, such as benzoic and terephthalic acid.
We also include a detailed discussion of the capabilities and limitations
of the model in context and related to previous investigations. Finally,
results are compared to observations from studies with other association
models