Development and application of a three-parameter RK–PR equation of state

In this work, we confirm the somehow previously expressed but not widespread idea that the limitations of cubic equations of state like Soave–Redlich–Kwong equation (SRK) or Peng–Robinson equation (PR) are a consequence of their two-parameter density dependence rather than of their empiric character. Moreover, it is shown that when combined with a simple generalized van der Waals attraction term, the van der Waals repulsion is more capable than the Carnahan–Starling term to follow the P v T behaviour of real fluids and, in particular, that the generalized Redlich–Kwong–Peng–Robinson (RK–PR) equation offers the best performance among cubic three-parameter density functionalities. A simple temperature dependence was developed and a straightforward parameterization procedure established. This simple – and optimized from pure compound data – three-parameter equation of state (3P-EoS) will allow in a later stage, by systematic study and comparison to other types of 3P-EoS, to find out what the actual possibilities and limitations of cubic EoS are in the modelling of phase equilibria for asymmetric systems.