Enthalpy and Heat Capacity Changes on Mixing: Fundamental
Aspects and Prediction by Means of the PPR78 Cubic Equation of State
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Abstract
The
PPR78 model is a predictive cubic equation of state relying
on the group-contribution concept. Our previous studies have highlightened
its capacity to predict the phase behavior of mixtures containing
a large variety of compounds: alkanes, alkenes, aromatic compounds,
permanent gases, sulfur compounds, etc. In this paper, it is attempted
for the first time to answer the question “<i>can the
PPR78 model be safely used in energy-rate balances?</i>”.
To do so, the largest possible number of enthalpy of mixing data and
isobaric heat capacity of mixing data were collected in the open literature
and predicted using the PPR78 model. It is shown that although certainly
perfectible, this model generally provides from acceptable to accurate
estimations of these properties depending on the nature of the mixtures
and the conditions of temperature and pressure as well. Furthermore,
this paper proposes some general reflections both on conceptual and
practical issues: Is it always possible to claim that the excess enthalpy
and the enthalpy of mixing are two strictly equivalent quantities?
Does an equation of state have the same capacity to reproduce enthalpy
of mixing data in one-phase and in two-phase regions? Which criterion
should be used for evaluating the accuracy of an equation of state
in terms of energy-rate balances