Enthalpy and Heat Capacity Changes on Mixing: Fundamental Aspects and Prediction by Means of the PPR78 Cubic Equation of State

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 “ can the PPR78 model be safely used in energy-rate balances? ”. 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?