Modification of Sako-Wu-Prausnitz equation of state for fluid phase equilibria in polyethylene-ethylene systems at high pressures

Gharagheizi, Farhad; Mehrpooya, Mehdi; Vatani, Ali

doi:10.1590/s0104-66322006000300012

Cited by 4 publications

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The EoS/G^EMixing Rules for Cubic Equations of State

Kontogeorgis

Folas

2009

Thermodynamic Models for Industrial Applications

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The range of applicability of cubic equations of state (EoS) (using the standard van der Waals one-fluid mixing rules) and g E models (especially the local composition ones) is illustrated in Table 6.1 and schematically also in Figure 6.1. In a somewhat simplified way, Figure 6.1 illustrates the advantages which may be obtained by combining the strengths of both approaches (i.e. the cubic EoS and the activity coefficient models) and thus having a single model suitable for phase equilibria (at least VLE) of polar and non-polar mixtures and at both low and high pressures. This combination of EoS and g E models has been possible via the so-called EoS/G E models, which are essentially mixing rules for, typically, the energy parameter of cubic EoS. These mixing rules permit the incorporation of an expression for the excess Gibbs energy g E (i.e. an activity coefficient model) inside the EoS, permitting thus a cubic EoS to be applied to polar compounds at high pressures as well.The starting point for deriving most (but not all) EoS/G E models is the equality of the excess Gibbs energies from an EoS and from a (successful) explicit activity coefficient model at a suitable reference pressure, P:where a suitable reference pressure P can be, for example, the infinite pressure (Huron-Vidal, Wong-Sandler models) or the zero pressure (e.g. MHV2, the PSRK models), while the superscript Ã refers to the specific activity coefficient model, e.g. NRTL. The right-hand part of Equation (6.1) is the g E expression of an explicit activity coefficient model, e.g. Wilson, NRTL or UNIQUAC (see Chapters 4 and 5), whereas the g E of the EoS is obtained from classical thermodynamics when the fugacity expression is known:

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