The Extended Crossover Peng–Robinson Equation of State for Describing the Thermodynamic Properties of Pure Fluids

Abstract

In this paper, a theoretical method has been introduced for developing the crossover Peng-Robinson (CPR) equation of state (EoS) which incorporates the non-classical scaling laws asymptotically near the critical point into a classical analytic equation further away from the critical point. The CPR EoS has been adopted to describe the thermodynamic properties of some pure fluids (normal alkanes from methane to n-butane and carbon dioxide) such as density, saturated pressure, isochoric heat capacity and speed of sound. Unlike the original method for the crossover transformation made by Chen et al. (Phys Rev A 42:4470-4484, 1990), we have proposed a procedure which adding an additional term into the crossover transformation to obtain the thermophysical properties at the critical point more exactly. It is shown that this new crossover method yields a satisfactory representation of the thermodynamic properties close to the critical point for pure fluids relative to the original PR EoS.

Modeling of the Mixture Critical Locus with a Modified Cubic Plus Association Equation of State: Water, Alkanols, Amines, and Alkanes

“…Equations of state are important tools in process simulation due to their ease of implementation and versatility. Cubic equations of state, the most successful of these models are, however, unable to completely describe the critical point of a compound or mixture, , especially in terms of volumetric properties, without the use of specific treatments, e.g., crossover methods. − These volumetric problems are not limited to the near-critical region, as the values for the covolumes of these equations of state are small, which leads to an overprediction of . , Their limitations are even more evident for systems where hydrogen bonding is important.…”

Application of the functional renormalization group method to classical free energy models

“…Phenomenological approaches have been used to combine the results of this work with classical thermodynamic models in order to construct a free energy model that has the correct scaling behavior in the critical regime and the classical behavior of the original model away from the critical point. This crossover approach has been applied to several classical free energy models, including cubic equations of state, the perturbation theory for square‐well fluids, and statistical associated fluid theory (SAFT) …”